Conditions of Spontaneous Freezing of Supercooled Water

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Conditions of Spontaneous Freezing of Supercooled Water

Doucet, Y.; Brun, Edmond

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NATIONAL RESEARCH LABORATOHISS Ottawa, Canada TECHNICAL TRANSLATION D f v i s i o n of Mechanical E n g i n e e r i n g Pages

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P r e f a c e

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6

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Text.

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3 0 F i g u r e s

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4 Tech, Trans, T T - 8 1 Date 19 O c t , o b e ~ , 1940,

Lab, OPdart !\To, ,= 5424A

F i l e

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12-aR4-22

T i t l e : C ~ n d f t ~ i o n s de e s s s a t i o n spcrntaneee de l a s u r f u s i o n de l b e a u ,

By :

Y e

Doucet, P r e f a c e by Edmond Brun,

Reference: Note Technique No, 35, French C;umzittee f o r t h e Development of A e r o n a u t i c a l R ~ S F . R P C ~ ( G ~ F?<, A d )

Paris, 1 9 4 6 ,

S u b j e c t : CONDITIONS OF SFONTAIEOUS FHE3ZIYCS OF STJFT2H- COOLED YiATTiR, S u b m i t t e d by: J, L o O P P , T r a n s l a t s d by: Head, D,,

A,

S i n c l a l r Low Temperature L a b o ~ a t o r y , Approved by:

J, H,

P a r k i n , D i r e e t o r ,

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Page

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( i i ) Tech, T r a n s , TT-81 T A B U OF CONT3NTS Page P r e f a c e ( i v ) A b s t r a c t ( v i i

Chap, I H i s t o r i c a l Survey of t h e Problem E

2 , The I n v e s t i g a t i o n s of 5, Dorsey 2 Chap, 11 Apparatus f o r t h e Xxperiments 4 3, The A d j u s t a b l e Temperature Bath 4 4 , The Thermocouple and Recording

Device 4

5, The L a b o r a t o r y Tube 5 Chap, I11 R e s u l t s of t h e Measurements 7

A

-

A c t i o n of E x t e r n a l F a c t o r s 6 , E f f e c t of t h e M a t e r i a l of t h e V e s s e l "P 7, E f f e c t of H e t e r o g e n e i t y of Tem- p e r a t u r e ( ~ e t h o d of Coolfng) 8 8 , E f f e c t of t h e Rate of Cooling 9 9 , E f f e c t of t h e Volume of Water 10 1 0 , E f f e c t of t h e P r e s e n c e of t h e Couple 1 2 11, E f f e c t of A g i t a t i o n 13 1 2 , Conclusions Regarding t h e E x - t e r n a l F a c t o r s I n v e s t i g a t e d 13

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Action o f I n t e r n a l F a c t o r s 13, E f f e c t o f t h o Kind o f Water 1 4 1 4 , The E f f e c t of A i r i n S o l u t i o n 1 4 1 5 , E f f e c t o f P r e - h e a t i n g 15 1 6 , Effojct o f S a l t s i n S o l u t i o n 1 6 1 7 , E f f e c t o f t h e P r e s e n c e o f F i n e P a r t i c l e s Suspended i n t h e Water 18 Chap, I V I n t e r p r e t a t i o n o f t h e E x p e r i m e n t a l R e s u l t s 24 18, E f f e c t of an I c e C r y s t a l 24 1 9 , E x t e n t o f t h e S u p e r c o o l i n g 24 20. F a c t o r s F a v o u r i n g t h e Growth o f t h e M o l e c u l a r Aggregate 25 21, The E f f e c t o f P r e - h e a t i n g o n L i q u i d s Other t h a n Water 26 2 2 , S t a b i l i t y o f t h e S u p e r c o o l i n g 27 B i b l i o g r a p h y 29

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Tech, Trans. TT-81

I t i s w e l l known t h a t whatever t h e i r n a t u r e the d e p o s i t s of i c e which form on a i r c r a f t i n f l i g h t adhere s t r o n g l y t o t h e s u r f a c e s o f t h e machine. To d a t e i t h a s been p o s s i b l e t o o b t a i n o n l y v e r y complex and o f t e n unex- p e c t e d r e s u l t s from measurements o f t h e adhesive f o r c e s o f f r o s t on s o l i d s u b s t a n c e s , I n o r d e r t o b r e a k t h e p r e s e n t deadlock i t would appear e s s e n t i a l t h a t t h e s t u d y of t h e s e f o r c e s s h o u l d b e preceded by the s t u d y o f t h e mechanism o f f r o s t f o r m a t i o n , and, more g e n e r a l l y , by t h e s t u d y o f t h e c o n d i t i o n s under which the f r e e z i n g o f s u p e r c o o l e d w a t e r o c c u r s . No doubt t h e road ahead i s a l o n g one b u t t h e a t t a i n m e n t of t h e g o a l w i l l be made more c e r t a i n .

The phenomenon of t h e s u p e r c o o l i n g o f water i s a l t o g e t h e r commonplace; i t h a s been known s i n c e t h e

a c c u r a t e measurement o f t e m p e r a t u r e s became p o s s i b l e , Never- t h e l e s s i t s e x p e r i m e n t a l s t u d y h a s s t i l l t o be completed, and more d a t a a r e a v a i l a b l e on t h e s u p e r c o o l i n g o f c e r t a i n r a r e s u b s t a n c e s i n o r g a n i c c h e m i s t r y t h a n on t h a t o f w a t e r ,

This i s due t o t h e g r e a t r a p i d i t y w i t h which w a t e r c r y s t a l l i z e s , making i t d i f f i c u l t t o observe t h e t r a n s f o r m a t i o n from water

t o i c e .

However, a r e c e n t American paper (Dorsey,

1938) f u r n i s h e d some i n t e r e s t i n g r e s u l t s

,'

which were p a r t i a l l y v e r i f i e d by t h e w r i t e r i n 1939. The w r i t e r t h e n proposed t o M r , Doucet t h a t he f o l l o w up M r . D o r s e y r s work, i n t r o d u c i n g c e r t a i n improvements. The r e s u l t i n g s t u d y i s t h e s u b j e c t o f t h e p r e s e n t paper.

I n view o f h i s t h e s i s on c r y s t a l o m e t r y ,

M r . Doucet was p a r t i c u l a r l y w e l l q u a l i f i e d t o u n d e r t a k e such an i n v e s t i g a t i o n . The f o l l o w i n g w i l l show what an ample documentation of e x p e r i m e n t a l r e s u l t s he h a s succeeded i n assembling i n t h e c o u r s e o f a y e a r ' s work, However, i n a q u e s t i o n a s complex a s t h a t under review, i t would be o f l i t t l e u s e t o c a r r y o u t a l a r g e number o f experiments i f e a c h were n o t p e r f e c t l y d e f i n e d and i f , i n s t u d y i n g t h e i n f l u e n c e o f one parameter, c a r e were n o t t a k e n t o keep t h e o t h e r s cons tent. M r . Doucet f s e x p e r i m e n t a l t e c h n i q u e i s s o s u r e t h a t i t h a s been p o s s i b l e t o d r a w numerous c o n c l u s i o n s , some a l r e a d y a c c e p t e d , o t h e r s new, from h i s measurements,

N e v e r t h e l e s s t h e experiments a r e f a r from com- p l e t e and M r . Doucet's i n t e r p r e t a t i o n s o f t h e r e s u l t s a l r e a d y o b t a i n e d must be c o n s i d e r e d p r o v i s i o n a l . These embryonic

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Tech. Trans.

tk_eor.ies, however, apart from t h e i r i n t r i n s i c i n t e r e s t , prr-ovide a n o r i e n t a t i o n f o r t h e coming r e s e a r c h e s , which may

p o s s i b l y psrmit s r e c t i o n o f t h e e d i f i c e on the ground t h a t has now been ex-l.a.vnted, B u t can p r o g r e s s b e a t all r a p i d

ir, the s t u d y of w ~ t ~ r , k l ~ i ~ p u r e substarico which has such

complex p r o p e r t i e s ?

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Tech, Trans, T T - 8 1

ABSTRACT

Chapter I g i v e s a h i s t o r i c a l s u r v e y o f t h e problem, The most advanced s t u d y 91-though s t i l l incom- p l e t e , i s t h a t of E, Dorsey (19385, of which t h e fundamental r e s u l t i s t h e demonstration of a spontaneous f r e e z i n g tem- p e r a t u r e assumed t o be s p e c i f i c f o r t h e sample of w a t e r under

i n v z s t i g a t i o n ,

Chapter I1 d e a l s w i t h t h e e x p e r i m e n t a l

a p p a r a t u s . The course o f t h e temperature d u r i n g t h e s u p e r - c o o l i n g o f t h e w a t e r i s r e c o r d e d p h o t o g r a p h i c a l l y , The s l o p e o f t h e curve g i v e s t h e r a t e of c o o l i n g a t each p o i n t of time and t h e s h a r p d e v i a t i o n shows t h e t e m p e r a t u r e a t which the s u p e r c o o l i n g c e a s e s ,

The r e s u l t s o f t h e measurements a r e g i v e n i n Chapter 111, I t i s found t h a t t h e spontaneous f r e e z i n g tem- p e r a t u r e of pure w a t e r v a r i e s w i t h t h e method and r a t e of c o o l i n g , the form o f t h e v e s s e l , and t h e volume of w a t e r ,

A r e l a t i o n s h i p i s e s t a b l i s h e d be tween an i n c r e a s e d s u p e r - c o o l i n g and a more g r a d u a l tempprature g r a d i e n t , A pre- h e a t i n g of t h e sample i n c r e a s e s t h e e x t e n t o f the super- c o o l i n g , S a l t s o l u t i o n s of low c o n c e n t r a t i o n w i t h s t a n d s u p e r c o o l i n g s e q u a l t o o r lower than t h o s e of pure w a t e r , depending on t h e n a t u r e of t h e s a l t , The t o t a l absence o f f i n e p a r t i c l e s suspended i n t h e w a t e r lowers t h e spontaneous f r e e z i n g t e m p e r a t u r e , I n Chapter I V a l l t h e f a c t s observed a r e e x p l a i n e d on t h e b a s i s o f B e r n a l and F o w l e r t s i d e a s about the composition of w a t e r , F i n a l l y two s t a t e s a r e d i s t i n g u i s h e d : f i r s t , a m e t a s t a b l e s t a t e down t o - 7 t o -8" f o r o r d i n a r y d i s t i l l e d w a t e r , and -11 t o -12O f o r w a t e r from w h i c h d u s t p a r t i c l e s have been removed by s p e c i a l means, then a l a b i l e s t a t e , i n 0s t w a l d ' s s e n s e , below t h e s e t e m p e r a t u r e s ,

I t i s d i f f i c u l t t o m a i n t a i n w a t e r i n t h e l i q u i d a t a t e a t t e m p e r a t u r e s below - 2 2 O ,

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Tech- T r h z l s T T - 8 1

CONDITIONS _=-. _".,-,--.-OF' SPONTANXOUS

---

FREEZING OF S U P E R C O O L S D 7.----

--

WATER

HIST(3FIICAL SURVEY OF THE PROBLEM

1, EARLY EXPERIMENTS =--

The s u p e ~ c o o l i n g o f w a t e r has been a known f a c t f o r a v e r y l o n g t i m e , F a h r e n h e i t o b s e ~ v e d t h e phenomenon as e a r l y a s 2

₁

21,, I n c o n n e c t i o n w i t h t h e c o n s t ~ . u c t f o n

o f h i s ther-rnometera he n o t e s t h a t one w i n t e r d a y - a t a

t e m p e r a t u r e o f 15°F ( = 9 , . 4 ° ~ ) b t h e w a t e r c o n t a i n e d ir. a small s e a l e d p h i a l was s t i l l l i q u i d , , On t h e o t h e r hand t h e f o l - lowing day t h e w a t e r c o n t t t l ~ e d . i n a d i f f e r e n t pklSaY we,s f r o z e n EN t - 6 , 7 O C ,

These e x p s r f m e n t s were t a k e n up agafrl b y

i n 1788 In a mannera t h a t was c o n s i d e r a b l y more c , IJe s t u d i e d n o t a b l y , t h e i n f l u e n c e o f s a l t s i n s o 1 u t ; o n and s o u g h t t h e d i f f e r e n t means which would b r i n g a b o u t a c e s s a t i c n cjf s u p e r c o o l i n g , The g r e a t e s t o b s e r v e d s u p s r c o o l f n g was IIaC,

I t i s n e c e s s a r y t o t u r n n e x t t o

--

uss sac^)

--=

(1.936) t o d i s c o v e r a n o t h e r i n v e s t i g u t i o n of' t h e supel7cool1nb:, o f w a t e r . " ~ n d yt; t9

"

t h f ; ailthor- wrf t e s , " t h e s e condi t i c n s s r e r e a l i z e d by t h e p h g s f c l s t o n l y w i t h d i f f i c u l t y , The w a t e r m u s t b e purged ~ f afr, must b e p r o t e c t e d a g a i n s t a L l

a g i t a t i o n 5.n a bulb w i t h c a p f l l a r y o p e n i n g , o r i n

a

f l a s k be- n e a t h a l a y e r o f f i l l n ,

'',

I n an e x c e p t i o n a l c a s e he peaches

a t e m p e r a t u r e o f -22" w i t h o u t c e s s a t i o n o f t h e s u p e ~ c o o l l n g , ~ e s ~ r e t e 4 ) i n v e s t i g a t e d t h e t e m p e r a t u r e o f

maxirnunl d e n s i t y o f t h e w n t e r and s t u d f e d t,he v s r i a t i o n o f i t s volwne e v e n t e l c w z e r o d e g r e e , He r e p o r t s h a v i n g ob-

served w a t e r i n t h e l i q u i d s t a t e a t -200, b u t h f s measurements do n o t d e s c e n d below - g o ,

I s i d o r e p i e r r e 5 ) a g a i n employed t h e same

--- ---

e x p e r i m e n t a l arxBangenent f o r simf l a r f nves t i g a t i e n s ,

orb^,^)

-- p l a c e d w a t e r i n c a p i l l a r y t u b e s and e a s i l y o b t a i n e d s u p e r c o o l i n g ~ o f 6 O ,

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& f o u r 7 ) s t u d i e d more p a r t i c u l a r l y t h e super- c o o l i n g of w a t e r d r o p l e t s suspended i n a l i q u i d o f t h e same d e n s i t y ,

The works of v i o l e t t e 8 ) ,

--

ont ti^)

and -~ a r n e a l ~ ) .

-d i -d n o t g r e a t l y a-dvance t h e q u e s t i o n ,

Those of Vkite and T'winnfng15) d e a l t with the

measurements of v i s c o s i t y = t o - g Q O

The i n v e s t i g a t i o n s cf de Coppet i n 187514) on

s u p e r c o o l i n g i n r e l a t i o n t o s u p e r s t i ~ , r a t i o n l e d him t o a

k i n e t i c t h e o r y of t h e phenqmenon which he completed, in 1909, a f t e r c r i t i c a l e x a i n a t i o n by 0s twald,

The supercooling, experiment t h e n became

c l a s s i c a l , P e l l a t performed i t i n h i s c o u r s e a t t h e Sorbonne by p l a c i n g w a t e r once and f o r a l l i n a s e a l e d p h i a l which i s

f ~ ~ s e d o n t o t h e stem of a thermometer, When i t was cooled by t h e e v a p o r a t i o n o f e t h e r he r e p o r t e d t h a t t h i s a p p a r a t u s

p e r m i t s s u p e r c o o l i n g s of 80 t o be observed w i t h o u t d i f f i c u l t y , However, s i n c e t h e b e g i n n i n g o f t h e c e n t u ~ y t h e phenomenon h a s n o t . b e e n t h e o b j e c t . of any r e s e a r c h ,

Gernez, Tamman and many o t h e r s have s t u d i e d t h e s u p e r c o o l i n g of v a r i o u s s u b s t a n c e s b u t have n e v e r t a k e n - y p t h a t of w a t e r , Some experiments o f Bigelow and R Y k e n b o e r L G ) s h o u l d be c i t e d , however ,

THE INVESTIGATIONS OF E 0 CORSEY

Eo ~ o r s e ~ 2 4 ) p u b l i s h e d an i n t e r e s t i n g b u t i n - complete work i n 1938, The new r e s u l t a t whi ch he a ~ r f v e s i s t h e e x i s t e n c e of a p e r f e c t l y d e f i n i t e , spontaneous f r e e z i n g temperature which i s c h a r e c t e r i s t i c of t h e w a t e r sample under i n v e s t i g a t i o n ,

He experiments on t h i r t y - s e v e n samples o f w a t e r of d i f f e r e n t o r i g i n : swamp w a t e r , s p r i n g w a t e r , w a t e r from a r e s e r v o i r , d i s t i l l e d w a t e r , e t c , The spontaneous f r e e z i n g t e m p e r a t u r e s range from -3" t o - 7 , 7 O , t h e n from -10,7O t o -21°,

Dorsey a t t a c h e s c o n s i d e r a b l e Importance t o t h e t h e o r y o f " n u c l e i " , By t h a t he does n o t mean Gernez and Tamman's n u c l e i , b u t r a t h e r t h o s e o f ~ a f f ~ l ~ ) , e , s o l i d p a r t i c l e s which a r e f o r e i g n t o t h e w a t e r and have no chemical o r c r y s t a l l i n e r e l a t i o n s h i p w i t h i c e , Ile e x p l a i n s h i s r e s u l t s above a l l by t h e shape of t h e n u c l e i , assuming t h a t

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1. t h e y d i m i n i s h i n i m p o r t a n c e a s a r e s u l t o f p r e v i o u s h e a t i n g ,

2 , t h e y dissolve s l o w i y i n time, and

h, t h e y a r e c a p a b l e of sudden a g g l o m e r a t i o n o r d i s s o c i a t i o n ,

E. run^^),

who had a l r e a d y i n p a r t resumed

t h e work of Dorsey, asked t h e p r e s e n t w r i t e r t o r e p e a t some of t h e measurements, d e f i n i n g t h e e x p e r i m e n t a l c o n d i t i o n s more c a r e f u l l y ( n a t u r e o f t h e w a t e r b e i n g examined, d e t e r - m i n a t i o n o f t e m p e r a t u r e and r a t e o f c o o l i n g , e t c , , ,), The r e s u l t s o b t a i n e d have b e e n i n t e r p r e t e d i n t h e l i g h t o f e x i s t i n g t h e o r i e s o f t h e m o l e c u l a r c o m p o s i t i o n o f w a t e r a s w e l l a s t h e e a r l i e r de Coppet-Ostwald " k i n e t i c theoryt' o f s u p e r c o o l i n g .

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Te ch

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Trans , TT- 0 1

Chapter

I1

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APPARATUS FCi-I TIIF: EXPERIMENTS

The a p p a r a t u s c o n s i s t s of a n a d j u s t a b l e tern- p e r a t u r e b a t h , a thermocouple

,

a p h o t o g r a p h i c r e c o r d i n g device and a l a b o r a t o r y t u b e ,

THE ADJUSTABLX !TEMPERATURE BATH

-

The a d j u s t a b l e temperature b a t h i s based on ~ a l a n d e f B ~ O ) l i q u i d a i r c r y o s t a t , The c o o l i n g a g e n t i s d r y i c e , c o n t a i n e d i n t h e Dewar f l a s k no, 1 ( F i g , 1) , Acetone i s poured i n t o t h e Dewar f l a s k ,

-

2 , i n Ghich i t can be s t i r r e d by a c u r r e n t of compressed a i r , The vacuum w i t h i n t h e double w a l l may be a d j u s t e d a t w i l l so a s t o modify t h e thermal

exchange s o A h e a t i n g r e s i s t a n c e p e r m i t s t h e c o o l i n g o f t h e acetone t o be r e t a r d e d and even e n a b l e s t h e temperature t o be k e p t c o n s t a n t w i t h i n a p p r o x i n ~ a t e l y a t e n t h o f a d e g r e e , owing t o t h e p r e s e n c e of an atmospheric t h e r m o r e g u l a t o r w i t h iron-mercury c o n t a c t , The a p p a r a t u s i s h i g h l y a d a p t a b l e , p e r m i t t i n g e i t h e r r a p i d o r very slow c o o l i n g o f t h e b a t h , o r a l l o w i n g i t s temperature t o be k e p t c o n s t a n t , o r a g a i n e n ~ b l i ~ g i t t o be r e - h e a t e d more o r l e s s r a p i d l y ,

TIIE Tm:HMOCOUPLE AND R E C O R D I N G DEVICE

The temperature i s measured by a couple c o n s i s t i n g of two s p e c i a l a l l o y s , BTE and CTE, from t h e Tmphy S t e e l Works, The s o l d e r e d j u n c t i o n i s immersed i n a m-ixture of w a t e r and i c e , The e l e c t r o m o t i v e f o r c e i s

measured by a f'Meci" double c i r c u i t p o t e n t i o m e t e r w h i c h i s

s e n s i t i v e t o a t e n t h o f a m i c r o v o l t , The " F o u r e t i e r " g a l -

vonometer ( ~ e r n i k e t y p e ) i s c o n s t r u c t e d i n such a way a s p r a c t i c a l l y t o e l i m i n a t e t h e s u p e r f l u o u s t h e r m o e l e c t r i c f o r c e s ( g o l d w i r e s , copper-to-copper c o n t a c t s ) . I t h a s a remarkable zero s t a b i l i t y , I t can be made t o f u n c t t o n oelow i t s c r i t l c a l range by c o n n e c t i n g a r e s i s t a n c e i n s e r j e s , I t s s e n s i t i v i t y i s t h e n reduced t o t h e e n t i r e l y adequate v a l u e o f a cerltimetre p e r d e g r e e , The movements of t h e s p o t A r e r e -

corded by the Cambridge Company's " D r u m Camera", t h e dr.:ni of which i s a d j u s t e d s o a s t o e x e c u t e one r e v o l u t i o n p e r houra, The photographic p a p e r h a s a s e n s i t i z e d l e n g t h of 42 cm, and i t s width p e r m i t s d e f l e c t i o n s of 1 0 t o 11 cni,

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5

Tech, T r a n s , T T - 8 1

The thermopile i s c a l i b r a t e d between two f i x e d p o i n t s

-

t h e m e l t i n g p o i n t s of i c e and mercury, A

Roberteau thermometer g i v e s i n t e r m e d f a t e p o i n t s t o a hundredth of a degree a f t e r a l l c o r r e c t i o n s have b e e n made f o r emergent column and g r a d u a t i o n , The f o l l o w i n g t a b l e shows t h e r e s u l t s of t h e c a l i b r a t i o n :

It is found t h a t t h e p r o p o r t i o n t / e v a r i e s l i n e a r l y w i t h e , l e a d i n g t o t h e r e l a t i o n s h i p

( t i n d e g r e e s , e i n v o l t s ) ,

For t e m p e r a t u r e s of 1 5 t o 20° t h e p a r a b o l i c term has a b e a r i n g only on t h e hundredths and may t h e r e f o r e be n e g l e c t e d a t a l l times, The f o l l o w i n g w i l l t h e n be

w r i t t e n :

Wethin t h e range of t h e d e f l e c t i o n s specified

above, on t h e o t h e r hand, t h e l i n e a r r e l a t i o n s h i p

Is found, The d e f l e c t i o n ,

a

,

expressed i n m f l l i m e t k e s , i s

measured on t h e photographic paper which has been developed and d r i e d slowly between s h e e t s of f i l t e r paper, Constancy i n t h e q u a l i t y of t h e paper and i n i t s h a n d l i n g mean t h a t d e s p i t e t h e shrinkage d u r i n g d r y i n g , measurements m a y be guaranteed t o an accuracy of h a l f a m i l l i m e t r e o r l e s s ,

From e q u a t i o n s (1) and ( 2 ) it f o l l o w s t h a t

THE

LABORATORY TUBE

The l a b o r a t o r y tube i s a t e s t tube of o r d i n a r y g l a s s , pyrex o r q u a r t z , washed i n a b o i l i n g sulphochromic mix-

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6

t'nrough a p a r a f f i n e d s t o p p e r , i s immersed i n t h e t e s t w a t e r ,

A t u b e of copper was a l s o employed, e i t h e r v e r t i c a l l y o r h o r i z o n t a l l y , and t h e couple was t h e n i n t h e r m a l c o n t a c t

w i t h t h e w a l l s , F i n a l l y s e a l a d t u b e s w i t h e x t e r n a l c o u p l e s were employed,

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7

Tech, T ~ a n s , TTc-81

RESULTS OF THE MEASU REhTEMTS

A

-

A C T I O N O F SXTERNAL FACTOdS

A l l t h e measurements g i v e n i n S u b s e c t i o n A

r e l - a t e t o water = a t h a s been twice d i s t i l l e d , The a t e y =mmtti& second d i s t i l l a t i o n (Lafourcade a p p n m t u s 2 2 ) _{- -} is n o t k e p t l o n g e r than e i g h t days,

e 0

EFFECT OF THE =-. M k F 2 R I A L OF THE VESSEL

The e x p e r i m e n t a l p r o c e d u r e ( t h e same i n a l l c a s e s ) i s a s f o l l o w s : With t h e t e s t t u b e c o n t a i n f n g t h e w a t e r and t h e themnocoupbe i n p l a c e i n t h e a c e t o n e b a t h , t h e ambient t e m p e r a t u r e i s t a k e n a s t h e s t a r t i n g p o i n t , The h e a t i n g c i r c u i t f s c u t S Q t h a t t h e t e m p e r a t u r s d r o p s r a p f d l y , b u t

from a few d e g r e e s above z e r o t h e i n t e n s i t y o f t h e c u r r e n t

i s a d j u s t e d i n such a way t h a t t h e c o o l i n g r a t e is o f t h e o r d e r o f h a l f a d e g ~ e e pep mfnute, The movement of t h e s p o t i s t h e n r e c o r d e d , E'igure 2 g i v e s an example of t h e c u r v e s o b t a i n e d , The sudden r i s e o f t h e s p o t towards t h e z e r o l i n e i n d i c a t e s t h e spontarleous f r e e z i n g of t h e w a t e r ,

A t t h i s moment t h e r e c o r d i n g i s b r o k e n o f f and t h e f n t e n s f t g o f t h e h e a t i n g c u r r e n t 1s s u i t a b l y a d j u s t e d so t h a t t h e t e m p e r a t u r e r i s e s a g a i n t o approxfmately +5 or

+ 6 O . A f t e r t e n rnfnutes t h e r e i s no f u r t h e r t r a c e of I c e , A

new f r e e z i n g i s t h e n begun undela i d e n t i c a l c o n d i t f o n s ,

Wfth a pyrex tube c o n t a i n i n g 7 c c , o f w a t e ~ t h e f o l l o w i n g spontaneous f r e e z i n g t e m p e r a t u r e s were noted:

Wfth a tube o f t h e same d i a m e t e r , b u t o f o r - d i n a r y g l a s s , t e m p e r a t u r e s of

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8

Tech, T r a n s , T T - 8 1

I n a q u a r t z tube -7,3EI0 was o b t a f n e d , and i n a copper tube of s l i g h t l y s m a l l e r d i a m e t e r (10

mm,

i n s t e a d of 1 2 mm,), -7,4OoO

F f n a l l y i n a t e s t tube which had n o t been washed i n t h e sulphochrornic m i x t u r e , -7,28" was r e c o r d e d ,

The water always f r e e z e s i n t h e neighbourhood of -7,30°, The l a g k of e f f e c t Y o f t h e w a l l s i s e v i d e n t , i n s p i t e of Dufour qs.'S opinion,

a) Using t h e d r y - i c e c r y o s t a t and workfng w i t h 7 cc, volumes of w a t e r and c o o l f n g r a t e s of t h e o r d e r of' O O l o p e r mfnute, t h e c o u p l e , whf ch was immersed i n t h e w a t e r , f n - d i c a t e d t h e folloivfng s u p e r c o o l f n g s a t the moment of f r e e z i n g :

Another s e r i e s gave

7 0 1 5 0 9 7,06O, 7,23O, t h e n

and f i n a l l y

With t h e one e x c e p t i o n o f a f r e e z i n g a t c-5,484

t h e spontaneous f o r m a t i o n of i c e took p l a c e between -7,84"

and -7.61°, The g e n e r a l mean i s -7,28O,

b ) The f i r s t measurements were n o t made With;,the

a p p a r a t u s p r e v f o u s l y d e s c r i b e d , b u t were c a r r i e d o u t more simply b y p l a c i n g t h e l a b o r a t o r y tube i n a l a r g e t e s t tube

-

which formed a Y'sleevev' of a i r , This l a t t e r tube i n t u r n

was immersed i n t h e e u t e c t i c m i x t u r e of i c e and ammonium c h l o r i d e ( - 1 5 0 ) o r i n a m i x t u r e of i c e and calcium c h l o r i d e , A Roberteau thermometer, g r a d u a t e d i n t w e n t i e t h s of a d e g r e e , was immersed i n t h e w a t e r sample w i t h o u t coming i n t o c o n t a c t w i t h t h e tube ( F i g , 3 ) a

There i s l i t t l e d i f f e r e n c e i n t h e e x p e r f m e n t a l p r o c e d u r e , The t e s t t u b e , s t i l l c o n t a i n i n g 7 cc, of w a t e r , i s

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9

Tech, T r a n s , TT-81 dipped i n a b a t h a t z e r o d e g r e e s b e f o r e b e i n g p l a c e d i n t h e l a r g e t e s t t u b e , With t h e a i d o f a s t o p - w a t c h t h e t e m p e r a t u r e i s n o t e d from moment t o moment, The r a t e o f c o o l i n g i s a g a i n o f t h e o r d e r of 0,1° p e r minute a t t h e i n s t a n t o f f r e e z i n g . A f t e r t h e s u p e r c o o l i n g h a s c e a s e d t h e tube i s exposed t o t h e

ambient t e m p e r a t u r e u n t i l m e l t i n g of t h e i c e i s complete, and i s t h e n t e s t e d once more,

The f o l l o w i n g a r e t h s s u p e r c o o l i n g s which were s u c c e s s i v e l y observed:

On a n o t h e r sample of t h e same w a t e r 6,67O, 5,85O and 6,33"

were o b t a i n e d , and a g a i n

5,480, 4,45O and 5,8400

E x c e p t f o r two s l i g h t l y s m a l l e r r e s u l t s i t i s s e e n t h a t t h e f r e e z i n g o c c u r r e d s p o n t a n e o u s l y between -5,82O and -6.67O, The g e n e r a l mean i s - 6 0 0 7 0 0

There i s a s y s t e m a t i c d i f f e r e n c e o f t h e o r d e r o f 1,20° from t h e r e s u l t s o b t a i n e d w i t h t h e p r e v i o u s e x p e r i m e n t a l p r o c e d u r e , Now, a thermometer p l a c e d i n t h e a i r which s u r r o u n d s

t h e w a t e r tube i n d i c a t e s t e m p e r a t u r e d i f f e r e n c e s o f 3 t o 4O, depending on whether t h e b u l b i s above o r below t h e s l e e v e o f a i r . Such d i f f e r e n c e s do n o t o c c u r w i t h t h e s t i r r e d a c e t o n e b a t h , which e n a b l e s g r e a t e r s u p e r c o o l i n g s t o be a t t a i n e d ,

To sum up, depending on t h e method o f c o o l i n g employed, which d e t e r m i n e s t h e d e g r e e of h e t e r o g e n e i t y a

v a r i a t i o n i n t h e spontaneous f r e e z i n g t e m p e r a t u r e i s obsesved, o t h e r t h i n g s b e i n g e q u a l ( e o g o , 7,3O

2

0 0 3 0 , and 6 , l

2

0 , 3 ° ) ,

8, EFFECT OF

THE

RATE OF COOLING

The g r a p h i c a l r e c o r d i n g of t h e t e m p e r a t u r e c o u r s e p e r m i t s a c c u r a t e measurement of t h e r a t e o f c o o l i n g a t a g i v e n i n s t a n t ,

By c u t t i n g o f f t h e h e a t e n t i r e l y , and w i t h o n l y a s l i g h t vacuum i n t h e double-walled f l a s k , t h e dry i c e c o o l s t h e a c e t o n e b a t h a t a r a t e of t h r e e d e g r e e s p e r minute down t o z e r o d e g r e e s , The s u p e r c o o l i n g s a r e s m a l l and i r r e g u - l a r , r a n g i n g merely from 1 t o 3",

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1 0

Tech, Trans, TT-81

With a vacuum of approximately mm, of mercury and an o u t p u t of 5 w a t t i n t h e h e a t i n g c i r c u i t , t h e

r a t e of c o o l i n g i s of t h e c r d e r o f 0.5O p e r minute a t the time t h e zero p o i n t i s p a s s e d and O.1° p e r minute a t t h e i n s t a n t of f r e e z i n g , Under t h e s e c o n d i t i o n s a mean value of 7,3O was o b t a i n e d ,

A s t i l l slower c o o l i n g r a t e does n o t lower t h e f r e e z i n g t e m p e r a t u r e , For example 7,61° i s o b t a i n e d i n 56 minutes w i t h 001160 p e r minute a t the i n s t a n t t h e super- c o o l i n g ceased, t h e n 7,53O i n 77 minutes w i t h o n l y 0,024O p e r minute a t f r e e z i n g ,

The e x t e n t of s u p e r c o o l i n g does indeed i n - c r e a s e w i t h a d e c r e a s e i n the c o o l i n g r a t e , EIowever a t very slow r a t e s of c o o l i n g the e x t e n t of s u p e r c o o l i n g becomes i n - dependent of t h i s r a t e ,

SFFTCT OF THE VOLUME OF WATER

The t e s t tube i s r e p l a c e d by a small s p h e r i c a l f l a s k c o n t a i n i n g 28 c c , water. F r e e z i n g t a k e s p l a c e a t

-2,82O, -3,73O and -2,28O,

A thermometer p l a c e d

i q

t h e c o o l i n g b a t h r e g i s t e r s

-7,3O, -7,5O and -7,4O r e s p e c t i v e l y ,

Thus t h e w a t e r i n c o n t a c t w i t h t h e w a l l was a t a temperature of approximately -7O a t t h e time when t h e w a t e r a t t h e c e n t r e was s t i l l o n l y a t -So, C r y s t a l l i z a t i o n must have begun a t a p o i n t on the w a l l ,

An a t t e m p t was a l s o made t o reduce t h e volume of water t o t h e minimum r e q u i r e d f o r immersion of t h e s o l d e r e d

j u n c t i o n of t h e c o u p l e , i , e , ,

1,s

c c , The same f r e e z i n g tem- p e r a t u r e was found a s f o r 7 c c , , namely

-7,45O, -6,92O and -7,2500

However, i t i s p o s s i b l e t o reduce t h e volume of w a t e r s t i l l f u r t h e r t o a few cubic m i l l i m e t r e s by t h e

t e c h n i q u e of drops suspen ed i n a l i q u i d of t h e same d e n s i t y ,

B

This was D u f o u r T s method7 f o r f r e e i n g t h e w a t e r from tihe

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11 Tech, T r a n s , TT-81 e f f e c t of c o n t a c t with t h e w a l l s , Our a p p a r a t u s f o r r e c o r d f n g t h e thermal e f f e c t of t h e c e s s a t i o n of s u p e r c o o l f n g is no l o n g e r s u i t a b l e , I n i t s p l a c e v i s u a l o b s e r v a t i o n o f t h e f r e e z i n g must be employed,

For t h i s purpose t h e opaque d r y i c e i s r e p l a c e d b y l i q u i d a i r and t h e i n s i d e Dewar f l a s k i s c m p l e t e l y

e v a c u a t e d b y means of a m o l e c u l a r pump w i t h l i q u i d a i r t r a p and d e g a s i f y i n g of t h e g l a s s a t 500°, A m i x t u r e o f l i n s e e d o i l and c l o v e o i l was t r i e d b u t i t becomes opaque v e r y q u i c k l y , The benzol-chloroform m i x t u r e s o l i d i f i e s a t

-a0

and i s t h e r e - f o r e u n s u i t a b l e , Acetone and chloroform, on t h e o t h e r hand, would p e r m i t very low t e m p e r a t u r e s , b u t u n f o r t u n a t e l y w a t e r

i s s o l u b l e i n the a c e t o n e , F i n a l l y , a m i x t u r e o f t r a n s f o r m e r o i l ( d = 0,875) and chloroform ( d = 1,526) proved s a t i s f a c - t o r y , The a p p a r a t u s was i l l u m i n a t e d t r a n s v e r s a l l y by a lamp and the s m a l l t r a n s p a r e n t d r o p l e t s could be s e e n very c l e a r l y f l o a t i n g i n t h e c e n t r e of t h e yellow-amber l i q u i d , The thermocouple was s t i l l employed t o r e c o r d t h e t e m p e r a t u r e , and when- e v e r a d r o p became opaque t h e t h e r m o e l e c t r i c c u r r e n t was c u t o f f f o r a s h o r t p e r i o d , A f t e r t h e f i l m had been developed t h e t e m p e r a t u r e s of a l l t h e s h a r p a n g l e s were marked, These range from -11° t o -2Z0, The experiment, which was r e p e a t e d s e v e r a l t i m e s x ) , i n one c a s e gave t h e f o l l o w i n g r e s u l t s : l a r g e drop of a p p r o x i m a t e l y 6 mm, d i a m e t e r , -11,720 : drop o f - 4 mm, d i a m e t e r , -16,23O; s m a l l e r d r o p s , s u c c e s s i v e l y , - 1 7 0 3 5 0 , -18,34°, -19,13O;

c h a i n of' cont iguous d r o p l e t s

,

-20,80°; f i n a l l y , t h r e e remaining f i n e d r o p l e t s , s i m u l t a n e o u s l y , -21,6Z0, Hence, t h e s m a l l e r t h e d r o p l e t , t h e g r e a t e r t h e s u p e r c o o l f n g , These experimen s s h o u l d be c o n s i d e r e d i n 6j c o n n e c t i o n w i t h t h o s e o f S o r b y on c a p i l l a r y t u b e s , Sorby o b t a i n e d s u p e r c o o l i n g s of 60 i n t u b e s o f 6 mm, t o 0 , 6 rnm, d i a m e t e r and o f 17O when t h e d i a m e t e r was reduced below 0 , 1 ,

Thus, d e s p i t e D o r s e y D s o p i n i o n , i t i s un- d e n i a b l y t r u e t h a t t h e supercoolinp; i s f a v o u r e d by a v e r y s m a l l volume o f w a t e r ,

x)

The sudden, s u c c e s s i v e f o r m a t i o n s o f t h e s e s m a l l i c e p e l l e t s a r e very odd, P r o j e c t e d on a s c r e e n t h i s would be an e x c e l l e n t e x p e r i - ment f o r d e m o n s t r a t i o n pukposaa,

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1 2

loo EFFECT OF THE PRESENCE OF THE COUPLE

I n a l l t h e measurements s o f a r g i v e n e i t h e r t h e couple o r a thermometer was immersed i n t h e w a t e r u n d e r i n v e s t j i g a t i o n , Dorsey, l i k e a l l h i s p r e d e c e s s o r s s i n c e

F a h r e n h e i t , employs s e a l e d v i a l s and measures t h e t e m p e r a t u r e o f t h e b a t h , Now, s i n c e t h i s b a t h which c o o l s t h e w a t e r i s a t a lower t e m p e r a t u r e , a l l tho r e s u l t s a r e marred b y a

s y s t e m a t i c e r r o r i n e x c e s s , However, i f t h e r a t e o f c o o l i n g i s s u f f i c i e n t l y slow and i f t h e w a t e r , i n r a t h e r s m a l l q u a n t i t y , 1 3 p l a c e d i n a s t r e i g h t t u b e , t h e d i s c r e p a n c y can be c o n s i d e r e d n e g l i g i b l e , I n f a c t , w i t h t h e a p p a r a t u s employed i n t h e s e e x p e r i m e n t s t h e u s u a l r a t e o f c o o l i n g was 0 0 2 t o 0,3O, I n t h e c a s e o f t h e s p h e r i c a l f l a s k o f t h e p r e v i o u s s u b s e c t i o n , however, i t was s e e n t h a t t h e d i f f e r e n c e r o s e t o s e v e r a l d e g r e e s , To s e t up e x p e r i m e n t s o f t h i s k i n d w i t h g r a p h i c a l r e c o r d i n g o f t h e f r e e z i n g i t i s n e c e s s a r y t o have t h e c o l d s o l d e r e d j u n c t i o n o f t h e c o u p l e i n t h e r m a l c o n t a c t w i t h t h e w a l l o f t h e t u b e . A copper t u b e i s more s u i t a b l e t h a n a g l a s s one, The f o l l o w i n g a r e t h e r e s u l t s o f some o f t h e s u p e r c o o l i n g s s o o b t a i n e d : On a n o t h e r sample:

A week l a t e r , w i t h t h e same w a t e r which had remained i n t h e t u b e ,

wre o b t a i n e d , Another s e r i e s gave

Even i f a t e m p e r a t u r e d i s c r e p a n c y between t h e

.

tube and t h e w a t e r of some t e n t h s o f a d e g r e e be t a k e n i n t o a c c o u n t , i t i s c e r t a i n t h a t t h e o b s e r v e d u p e r c o o l i n R s a r e d i s t i n c t l y g r e a t e r i n t h e absence o f a thermometer. The g e n e r a l mean i s 10,6O i n t h e f i r s t c a s e a n d 7,3O i n t h e s e c o n d ,

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Ilo

EFFECT OF A G I T A T I O N

A t any g i v e n s u p e r c o o l i n g t e m p e r a t u r e w a t e r i s e x t r e m e l y s e n s i t i v e t o shocks and v i b r a t i o n s , Thus a l i g h t c o l l i s i o n of t h e compressed a i r tube w i t h t h e t e s t t u b e , o r even w i t h t h e w a l l s of t h e acetone b a t h , causes i n - s t a n t a n e o u s c e s s a t i o n of t h e s u p e r c o o l i n g , I n o r d e r t o p r e - v e n t a c c i d e n t s o f t h i s k i n d t h e e n t i r e a p p a r a t u s used i n

t h e s e i n v e s t i g a t i o n s was s e t on a l a r g e stonework column which was d i r e c t l y imbedded i n t h e ground,

On t h e o t h e r hand, a g e n e r a l s t i r r i n g of t h e water does n o t brinly about f r e e z i n g , This f a c t h a s been

known f o r some time, I n 1866 V i o l e t t e wrote: "I was a b l e t o make a bubble of a i r move about t h e r e s e r v o i r ( a d i l a t o m e t e r w i t h s t e m ) , s l o w l y t o be s u r e , w i t h o u t c a u s i n g any change i n t h e liquid:" ILL t h e i r v i s c o s i t y measurements White and

Twinning employed s u p e r c o o l e d w a t e r which moved s l o w l y i n a c a p i l l a r y t u b e ,

CONCLUSIONS REGARDING THE EXTERNAL FACTORS INVESTIGATED I t appears p o s s i b l e t o e s t a b l i s h 9. c o r r e l a -

t i o n be tween a s m a l l e r t e m p e r a t u r e g r a d i e n t w i t h i n t h e w a t e r and a g r e a t e r s u p e r c o o l i n g .

I n f a c t , c o n s i d e r i n g once more t h e d i f f e r e n t r e s u l t s o b t a i n e d , o f t h e two methods of c o o l i n g employed i t

i s the one w i t h t h e s t i r r e d b a t h ( o f a c e t o n e ) which r e s u l t s i n t h e s m a l l e r g r a d i e n t , and which y i e l d s t h e g r e a t e r s u p e r - c o o l i n g t e m p e r a t u r e ,

An i n c r e a s e d c o o l i n g r a t e c e r t a i n l y c o r r e s p o n d s t o a l a r g e r g r a d i e n t and, by experiment, t o a s m a l l e r super- c o o l i n g , I f r a t e s o f c o o l i n g lower t h a n 0,1° p e r minute do n o t f u r t h e r i n c r e a s e t h e s u p e r c o o l i n g i t i s 110 doubt b e c a ~ s e

o f the f a c t t h a t f o r t h e volume of water employed ( 7 c c , ) , a slower r a t e no l o n g e r r e s u l t s i n a b e t t e r e q u a l i z s t i o n of t h e t e m p e r a t u r e s w i t h i n t h e l i q u i d , The e f f e c t of t h e volume o f w a t e r i s a l s o e x p l a i n e d , I n t h e s p h e r i c a l f l a s k t h e g r a d i e n t i s much g r e a t e r t h a n i n t h e t e s t t u b e , The s m a l l e r t h e d r o p s of w a t e r , t h e g r e a t e r t h e s u p e r c o o l i n g , S i m i l a r l y , t h e presence of a couple o r t h e r - mometer produces a g r e a t e r l o s s of h e a t i n i t s v i c i n i t y due

t o conduction and i n c r e a s e s t h e g r a d i e n t , Hence g r e a t e r s u p e r - c o o l i n g s a r e observed when t h e couple o r thermometer i s o u t - s i d e ,

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1 4

This e f f e c t of t h e g r a d i e n t can be v e r i f i e d b y s o e k i n g t o i n c r e a s e i t s y s t e m a t i c a l l y . For example, i f t h e b u l b o f t h e themlometer t c u c h e s t h e bottom of t h e t e s t tube -5,67O i s o b t s i n e d i n s t e a d *>f - 6 0 1 5 0 , I f t h e t e s t tube i t s e l f touches t h e c o l d w a l l s o f t h e a i r s l e e v e o n l y -3,25O

i s o b s e r v e d ,

TCI sun up:

a ) I f t h e e x p e r i m e n t a l c o n d i t i o n s remain un- chanp;ed t h e same s p e c t a n e o u s f r - ~ o z i n g t e m p e r a t u r e w i t h i n a p p r o x i m a t e l y s e v e r a l t e n t h s of a degree w i l l o c c u r w i t h g r e a t constancy, a s s t a t e d by Dorsey, e x c e p t f o r a n o m a l i e s , b ) Hcwever, t h i s spontaneous f r e e z i n g t e m p e r a t u r e i s n o t s p e c i f i c fox t h e sample u n d e r i n v e s t i g a t i o n , I t i s a f u n c t i o n o f t h s t e m p e r a t u r e g r a d i e n t , t h a t i s t o s a y , t h e r a t e and method of c o o l i n g and t h e form o f v e s s e l and volume of w a t e r employed,

B

-

A C T I O N OF INTERNAL FACTORS 130 EFFECT --*- O F THE K I N D OF VJATER

---

The u s u a l t w i c e - d i s t i l l e d w a t e r i s r e p l a c e d by w a t e r d i s t i l l e d i n t h e l a b o r a t o r ( n o , l ) , t h e n by

commorcial.ly distilled vvat,er ( n o , 27, and f i n a l l by w a t e r t a k e n d i r e c t l y i'~oan t h e c i t y w a t e r system ( z o o 3 7 .

Under t h e c o n d i t i o n s of t h e e x p e r i m e n t t h e

t w i c e - d i s t i l l e d w a t e r h a s a spontaneous f r e e z i n g t e m p e r a t u r e of - 7 , 3 Q 0 The o t h e r samples g i v e t h e f o l l o w l n g r e s u l t s :

Water no, 1: -7,5Z0, -7,12O, -7,3a0 mean: -7,34O;

W a t e ~ no, 2: -7,28O, -7,32O, -6,86O mean: -7,15"; Water no, 3: - 6 , 5 2 0 , -6,410, -G095O, -7,08O mean: -6,74°,

?he d i r f e r ~ n c e s due t o d i f f e r e n t o r i g i n s of t h e sample a r e so s l i g h t t h a t s y s t e m a t i c v a r i a t i o n s c m a o t be assumed,

':'ID3 EFF'ECT OF A I R I N SOLUTIOX

14,

-

--

Two s a r i 3 s o f complementary e x p e r i m e n t s were

c a r r i e d o u t , t h e f i r a t w i t h w a t e r s a t u r a t e d w i t h a i r , and t h e second w i t h w a t e r from whl s h t h e sir had been e l i m i n a t e d ,

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1 5 Tech, T r a n s , T T - 8 1 a ) Water S a t ~ x r a t e d w i t h A i r A d o u b l e - t u b e d f l a s k f i l l e d w i t h w a t e r was c o n n e c t e d t o t h e compressed a i r s y s t e m , w i t h i n t e r p o s i t i o n o f a c o t t o n f i l t e r , f o r t w e n t y h o u r s , The s u p e r c o o l i n g s measured w i t h t h e c o u p l e em2loyed e x t e r n a l l y were: b ) Water w i t h t h e A i r E l i m i n a t e d A f l a s k c o n n e c t e d t o a w a t e r j e t pump was immersed i n a t h e r m o s t a t a t 2500 The w a t e r b o i l e d f o r 9 h o u r s , The f o l l o w i n g morning, u n d e r t h e same c o n d i t i o n s a s above, t h e f o l l o w i n g s u p e r c o o l i n g s were r e c o r d e d : Thus t h e p r e s e n c e o r a b s e n c e o f a i r h a s no e f f e c t , The f i g u r e s o b t a i n e d a r e i n t h e same r a n g e a s t h o s e o f t h e p r e - c e d i n g p a r a g r a p h , 81agden2) s t a t e d t h a t o r d i n a r y w a t e r which f r o z e a t 23OF, f r o z e a t 21°F a f t e r b e i n g b o i l e d s t r e n u o u s l y f o r a c o n s i d e r a b l e p e r i o d , He e x p l a i n s t h i s , a s do numerous e x p e r i m e n t e r s a f t e r him, by t h e a b s e n c e o f a i r i n s o l u t i o n , The measurements g i v e n h e r e show t h a t t h i s e x p l a n n t l o n iz

f a l s e , A c t u a l l y t h e caust? i s t o b e found i n t h e e f f e c t o f r a i s i n g t h e t e m p e r a t u r e , EFFECT

-

O F PRE-mATING

-

_--.- Msasurements o f t h e d e g r e e of s u p e ~ c o o l i n g 22' a w a t e r sample gave: A f t e r t h i s snrnple h a d r e m a i n e d i n a t h e r m o s t a t . a t 85O f o r two h o u r s , t h e f o l l o w i n g r e a d i n g s were r e c o r d e d :

The w a t e r was r e t u r n e d t o t h e t h e r m o s t a t and l e f t 16 h o u r s , These s u p e r c o o l i n g s were t h e n o b t n i h e d :

(23)

Pago

-

i6

Tech, Trnns, TT-C31

I t v v : ~ k e p t a t 8S0 f o r a n c t h e r 18 h o u r s , but

t h e degree o f supercoolinp; d i d n o t i n c r e a s e :

1C,98Os 13,1Fj0; mean: 10.270e

Ths same w a t e r was a g a l n t e s t e d a month l a t e r ,

I t had ;:aevert;ed t o i t s

ripst

s u p e r c o o l i n g t e m p e r a t u r e :

7.24O, 7,3G0; mean: 7,30°,

'The e f f 7 e c t does n o t appeaa" t o be permanent,

---

cox1 t r a r y i;o Dorsey ! s s t a t e a e n t ,

AfterD b e i n g t a k e n o u t of t h e t h e r m o s t a t t h e w a t e r was r a p i d l y rccooleci, It was d e s i r e d t o s e e whether

t h e r e vsaa any "tempering" e f f e c t , b'or t h i s purpose t h e t e s t tube a t 8S0 Ivas p l a c e d i n a Dewar f l a s k w l t h wide opening and d i d n o t a t t a i n the m b i e n t t e m p e r a t u r e a g a i n u n t i l e i g h t

h o u r s l a t e r , The s u p e r c o o l i n g s t h e n 7bserved were a s f o l l o w s : 7,67O, 7,52O, 6,97OS 7.62?; mean: 7,4400

A slow r e c o o l i n g

-

d i d i n f a c t s u p p r e s s e f f e c t o f a s i x t e e n hour h e a t i n q ,

-

The e f f e c t o f a d d i n g o r d i n a r y w a t e r t o w a t e r t h a t h a s been h e a t e d was t h e n i n v e s t i g a t e d , I n a t e s t tube c o n t a i n i n g w a t e r which f r e e z e s a t -10,10° a few drops of

- r d i n a r y w a t e r were added, The m i x t u r e f r o z e a t -7,32*, Tlla 1-ff'ect i s t h u s d e s t r o y e d ;

--

t h e su$erc,oolii?g

-

i s t h a t o f

-

~ k ~ e asided wn-nkich had n o t been h e a t e d ,

--

.-

--=A-

-

"

---

16, S F E C T OF SALTS I N

--

SOLUTION

-

A l l t h e s a l t s o l u t i o n s s t u d i e d were made w i t h w a t e r which gave r e g u l a r s u p e r c o o l i n g s o f 7 , 3 O u n d e r t h e

experimt2ntal ccinditions d e s c r i b e d i n p a r a g r a p h 3 , The con--

c e n t r a t i o n s em1,loyed a r e i n a l l c a s e s s u c h t h a t t h e el-yc:,uop?c l o w e r i n g o f t e m p e r a t u r e remains o f t h e o r d e r o f s e v e r a l

h u n d r e d t h s o f a d e g r e e ,

Tile

--

s a l t s r a n g e tliemselves i n twc - - - - c l a s s & %

t h o s e which reduce t h e s u @ e r ~ o o l i ~ ~ and t h o s e which have no e f f e c t . A t no tims was any c l e a r i n c r e a s e of s u p e r c o c l . i n g observ.ed,

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1 7

Tech, T r a n s , TT-81 a ) S a l t s which r s d u c e t h e s a p e r c o o l i n q :

LiNOg s u c c e s s i v e s u p e r c o o l i n g s : 5.08O, 5.82O, 4.75O; TaC12 s u c c e s s i v e s u p e r c o o l i n g s : 5,85O, 6,030, 6*12O; CaSIZ s u c c e s s i v e s u p e r c o o l i n g s : 4,18O, 4,020, 5.08O; CD12 s u c c e s s i v e s u p e r c o o l i n g s : 4,25O, 5,12°, 6,08O. b ) S a l t s which have no e f f e c t : K C 1 o b s e r v e d s u p e r c o o l i n g : 7,38O; NaI o b s e r v e d s u p e r c o o l i n g : 6,72O; NaCl o b s e r v e d s u p e r c o o l i n g : 7,26O; Ca12 o b s e r v e d s u p e r c o o l i n g : 7,15O; RbI o b s e r v e d s u p e r c o o l i n g : 6 , 8 7 0 0 T h i s v a r i e d b e h a v i o u r w i l l b e c o n s i d e r e d s u b s e q u e n t l y , c ) The c a s e o f sodium a l g i n a t e : The raw s a l t , n o t d e p o l y m e r i z e d ( C 6 H 7 0 6 ~ a ) n H20 h a s a v e r y l a r g e m o l e c u l a r mass, t h e i n d e x n b e i n g c a p a b l e o f a t t a i n i n g 1000, Thus i t s s t x z l c t u r e d i f f e r s g r e a t l y from t h o s e o f t h e m i n e r a l s a l t s above, F u r t h e r m o r e t h e s o l u t i o n s a r e e x t r e m e l y v i s c o u s , a c o n c e n t r a t i o n o f two p e r c e n t a l r e a d y showing t h e v i s c o s i t y o f g l y c e r i n e , An i n v e s t i g a t i o n was made t o d i s c o v e r w h e t h e r t h i s p r o d u c t would c a u s e v a r i a t i o n s i n t h e s p o n t a n e o u s f r e e z i n g t e m p e r a t u r e o f t h e w a t e r , F i r s t s e r i e s : s p o n t a n e o u s f r e e z i n g tempera-

-

t u r e of t h e p u r e w a t e r : -7,3O; s o l u t i o n : 0 ~ 5 % ; s u p e r - c o o l i n g s s u c c e s s i v e l y r e c o r d e d :

Second s e r i e s : Nothing i s changed e x c e p t t h e k i n d of s o l u t i o n , which was o b t a i n e d from a n o t h e r sample o f

t h e a l g i n a t e , b u t was a g a i n b r o u g h t t o 0 0 5 $ ; o b s e r v e d s u p e r - c o o l i n g s :

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These two s s r i 6 s were n o t i n agreement, Other t e s t s were t h e n made usini; a d i f f e r e n t e x p e r i m e n t a l p r o c e d u r e ,

T h i r d s e r i e s ; T e s t tube r e p l a c e d b y a s m a l l tube of t h i n cop;ser; c x t e r n s l couple i n t h e r m a l c o n t a c t w i t h t h e t u b e , I t w i l l be i . - s c ~ l l e d t 5 a t u n d e r t h e s e c o n d i t i o n s t h e mean s u p e r c o o l i n g o f p u r e w ~ t e r i s 10,6°, Observed s u p a r c o o l i n ~ ; ~ w i t h a Q,E~$ s o l u t i o n were:

F o u r t h s e r i e s : This time a n o t h e r f a c t o r i s

--

m o d i f i e d , namely, t h e coo1fx-1 method, For t h i s purpose t h e a i r s l e e v e a p p a r a t u s (Fig, 3 7 is'employed, Under t h e s e con- d i t i o n s t h e spolitansou:; f r e e z i n c t e m p e r a t u r e o f p u r e w a t e r i s -6,070, For 0 , s p e r text s o l u t i o n s : Y t '

As:

The s u p e r c o o l i n g i s t h u s always s m a l l e r ( o n t h e a v e ~ a g e ) i n t h e p r e s s n c e o f a l g i n a t e t h a n i n i t s absence, e x c e p t Tor t h s f i r s t s e r i e s , However t h e d i s c r e p a n c y i s l e s s

t h a n t h a t which would ensu$ f r o p ?he s c a t t e r of t h e r e s u l t s , The c o n c l u s i o n i s c l e a r : -

The p r e s e n c e of s m a l l amounts o f sodium a l g i n a t e i n t h e w a t e r h a s p r a c t i c a l l y no e f f e c t on t h e spon- t a n e o u s f r e e z i n g c o n d i t i o n s of w a t e r ,

,FFECT OF THE PRSSEEICF O F FINE PARTICLES SUSPENDED I N THE WATER

I t w i l l f i r s t b e r e c a l l e d t h a t t h e r e i s no d i f f e r e n c e between t h e spontaneous f r e e z i n g t e m p e r a t u r e s of w a t e r which h a s been twice d i s t i l l e d , o r d i n a r y d i s t i l l e d w a t e r

and t h e w a t e r from t h e c i t y d i s t r i b u t i o n , The l a t t e r contaLns f a r more f i n e p a r t i c l e s i n s u s p e n s i o n t h a n distilled w a t e r anrl e s p e c i a l l y t w i c e - d i s t i l l e d w a t e r , I f t h e r e i s any a c t u a l

e f f e c t i t must be above a boundary which c o r r e s p o n d s t o watera which i s s t i l l more h i g h l y p u r i f i e d than t h e t w i c e - d i s t i l l e d v a r i e t y , To demonstrate t h i s e f f e c t r a t i o n a l e x p e r i m e n t s must be c a r r i e d o u t on w a t e r from which t h e d u s t h a s been remove d o

a ) Method o f Prolonged R e s t

Such a purpose may be a c h i e v e d a u t o ~ n a t i c a l l y by a l l o w i n g t h e w a t e r t o s t a n d f o r a c o n s i d e r a b l e tlme so t h a t t h e d u s t p a r t i c l e s a r e d e p o s i t e d due t o g r a v l t y , A f t e r s e v e r a l , weeks, a c c o r d i n g t o Dorsey, t h e water t a k e n from t h e s u r f a c e

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shows g r e a t e r s u p e r c o o l i n g s t h a n t h a t taken from t h e bottom,

A t a b l e of r e s u l t s seems t o b e a r o u t t h i s f a c t , b u t he a l s o r e p o r t s n e g a t i v e experiments,

The f i r s t experiments made d u r i n g t h e p r e s e n t i n v e s t i g a t i o n were a l s o n e g a t i v e , b u t a f t e r f o u r months of a b s o l u t e r e s t t h e water t a k e n from t h e s u r f a c e i s found t o have a mean spontaneous f r e e z i n g temperature of -9.34O

(9,45°, 9,62O, 8,950) and t h e waterb drbawn o f f through t h e stop-cock a t t h e bottom congeals a t a mean temperature of -7,2e0 (7,25O, 7 , 3 2 * ) , The d i f f e r e n c e i s 2 8 p e r c e n t , The water a t the bottom behaves l i k e o r d i n a r y water.

The q u e s t i o n a r i s e s whether t h e s i n g l e f a c t o r , w d u s t " , h a s been i s o l a t e d i n t h e s e oxperirnents, I t appears w i s e r t o approach the problem d i r e c t l y ,

b ) Method of S u c c e s s i v e F r e e z i n g s

I f a f i n e p a r t i c l e provokes t h e f o r m a t i o n o f an i n i t i a l m i c r o - c r y s t a l i t w i l l t h e n be imprisoned i n t h e s o l i d phase, The remaining l i q u i d , i f immediately decanted, should be p u r e r , A f t e r s e v e r a l o p e r a t i o n s of t h i s type water should be o b t a i n e d w i t h a spontaneous f r e e z i n g temperature lower than t h a t of t h e o r i g i n a l water.

There i s one d i f f i c u l t y i n d e c a n t i n g t h e un- congealed w a t e r , A t a s u p e r c o o l i n g of 7O the p r o p o r t i o n of i c e formed i s 7/bu, I t ought t o be p o s s i b l e , t h e r e f o r e , t o r e g a i n the 73/80 of the o r i g i n a l w a t e r , A s a m a t t e r of f a c t t h e i c e forms i n lorig n e e d l e s throughout t h e mass and im- p r i s o n s t h e water by c a p i l l a r y a c t i o n , Furthermore the t e s t tubk r e s t s i n an acetone b a t h a t -7O, and consequently t h e remaining water f r e e z e s r a p i d l y , I n t h e end, with an i n i t i a l q u a n t i t y of 10 c c , water only a few drops a r e ob- t a i n e d a f t e r the f i r s t f r e e z i n g ,

I n s t e a d of a w a i t i n g t h e spontaneous c e s s a t i o n of t h e s u p e r c o o l i n g i t i s provoked by a shock on t h e tube which i s removed from t h e c o o l i n g b a t h when the thermometer p l a c e d i n t h e water r e g i s t e r s - 5 O , The temperature i m e d i a t e l y r i s e s a g a i n t o O0 and s i n c e t h e ambient temperature i s g r e a t e r t h e f r e e z i n g doles n o t p r o g r e s s , The i c e n e e d l e s a r e p r e s s e d t o g e t h e r and t h e remaining water can be decanted. I t i s n e c e s s a r y t o a c t r a t h e r q u i c k l y so a s n o t t o allow water

f r o m the m e l t i n g of the i c e t o be added t o i t , A f t e r r e - p e a t i n g t h e o p e r a t i o n seven o r e i g h t times 30 t o 40 c c , water a r e o b t a i n e d , s a i d t o be t h a t of " t h e f i r s t f r e e z i n g " , A new

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Page .- 2 C

Ti3 cki , Trans , T Y - 81

c y c l e i s Lilrjn begun which p r o v l d e s 1 5 t o 20 cc. of w a t e r

I t ( f sec~iild f r a o e z l ng" , I n t h o end, a f t e r l e n g t h y h a n d l i n g ,

a ;r;iall qum1;I t y ~f w a t e r of f o u r t k k o r f i f t h f r e e z i n g I s

ot t a i n o d , 'I2le spontaneous f r e e z i n g t e m p e r a t u r e i s t h e n t ~ k e n , T e s t r l u , 1: w a t e r o f t l i ~ ~ e e f r e e z i n g s i n a

s s a l e d t u b e ; c c b l e d k y ar~ a c e t o n e b a t h which i s cooled i n cLlrn by G r y S z e ; r a t e of c o o l i n g : 0,1° p e r m i n u t e , Suc-

c e s s i v e ~ p o n l ; a . l = o u s f'reez1n.k t r ? m p e r l a t ~ ~ r e s o b s e r v e d , w i t h intemr1sdiai;cs r-e-heating t o +14O :

T e s t no, 2: wnter of f i f t h f r e e z i n g ; same

7

e x p e r i m e n t a l condl t i o n s :

T o s t n o , 3: w a t e r of f o u r t h f r e e z i n g ; same

-

experDimental procedure :

General mean of t h e three t e s t s : -10,71°0 Under t h e above c o n d i t i o n s o r d i n a r y d j s t i l l e d wnter shows a spontaneous f r e e z i n g t e m p e r a t u r e of -10,60°,

Thus t h o r e has been no change.

The f a i l u r e o f t h e p r e c e d i n g r e s u l t s rnay b e a t t r i b u t e d t o t h s s n l a l l number of p r i o r f'reezj.ngs o r t o t h e

f a c t t k , ~ i t , d u r i n g t h e experiment and i n t r a n s f e r from \ r e s s c l t o v e s s e l .the w a t e r i s expossd t o t h e a i r , and t h e r e ?is t h e n a tendency Tor d u s t p a r t i c l e s t o be pi[ cked up, Ae, 0.

r e s u l t . t11.i.s l o n g and complicated method was abandorirjd w;ci

methods of p u r i f i c a t i o n were employed whl.ch were csp:;.':1.~ ::f provid.ing "optic:ill y v o i d t t w a t e r , t o u s e t h e .t;ermlnolc,:y s f

t h e s p e c t r o s c o p i s t s ,

c ) Method of m t r a - f i l t r a t i o n

-

-. and E v a p o r a t i o n

---

2.n t h e Va':uum

T h r o u ~ h t h e c o - o p e r a t i o n of M r , ~ G r u b & ~ of t h e P e s t e u r I n s t i t u t e i t was posstblc? c o u s e h i s met;lo;i of'

u l t r a - f i l t r a t i o n . The c o l l o d i o r l n e m b c a ~ e s prepnl*ecl '23' hlri; have such f i n e p o r e s t h a t they l D a t a i i i c e r t a i n v i r u s e s w2icl.i had been c l a s s i f i e d as " f i l t e r - p a s s e r s " .

Fie rv;\ter fron: a d i s k i l l i n g aapphr:ltus T l r w a

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Page

-

21

Tech. Trans, T T - 8 1

i n t o a p h i a l . This t u b e , which i s 12 mm. i n d i a m e t e r and

6 cm. h i g h h a s p r e v i o u s l y been p r e p a r e d by caref'ul washing i n t h e sulpho-chromic m i x t u r e . As soon a s i t c o n t a i n s 4 t o

5 c c , u l t r a - f i l t e r e d w a t e r i t i s s e a l e d a t t h e blow p i p e . Another method, perhaps p r e f e r a b l e due t o t h e f a c t t h a t t h e a l r i s e x c l u d e d d u r i n g t h e o p e r a t i o n , h a s a l s o been employed, The r e q u i r e d apparaatus i s an o r d i n a r y U-tube which i s pr30vided w i t h a T-form d r i p n o z z l e ( F i g . 4 ) .

A f t e r thorough washing, a s w i t h t h e p h i a l j u s t d e s c r i b e d , i t i s p l a c e d under a d i s t i l l i n g a p p a r a t u s i n such a way t h a t t h e water flows i n t o p a r t ( a ) , The vacuum i s t h e n made by

drawing o f f t h e a i r through a v e s s e l c o n t a i n i n g s u l p h u r i c a c i d . The water from which t h e a i r h a s been d r i v e n o f f and which h a s been b o i l i n g , now condenses. A t t h i s moment t h e n o z z l e i s c l o s e d a t t h e blow-pipe, I n o r d e r t o o b t a i n a slow d i s t i l l a t i o n of the water i t i s now s u f f i c i e n t t o p l a c e p a r t ( b ) i n a m i x t u r e of i c e and w a t e r while s e c t i o n ( a ) r e - mains

at

t h e ambient temperature ( 1 7 0 ) ~ A f t e r f i v e or-six hours p h i a l ( b ) c o n t a i n s f o u r c c , condensed w a t e r . The

d i s t i l l e d r i n s e water of t h e tube may have c a r r i e d a few d u s t p a r t i c l e s which adhered t o t h e g l a s s . Thus t h e f i r s t c o n d e n s a t i o n water i s regarded a s a supplementary r i n s e and i s poured back i n t o compartrnont ( a ) , A second d i s t i l l a t i o n f u r n i s h s s water which i s p e r f e c t l y " c l e a n n . Tube ( b ) i s now s e p a r a t e d from t h e r e s t of the a p p a r a t u s a t t h e blow p i p e ,

A check on t h s p u r i t y i s made o p t i c a l l y by o b s e r v a t i o n of t h e l i g h t d i f f u s e d a t 90°, I f the image of an a r c l i g h t i s focused a t t h e c e n t r e o f t h e l i q u i d no Tyndall e f f e c t i s n o t e d , b u t only a s l i g h t opalescence due t o molecular d i f f u s i o n . Thus t h e l i q u i d i s p r a c t i c a l l y f r e e from v e r y f i n e p a r t i c l e s o r u l t r a - m i c r o s c o p i c d u s t p a r t i c l e s i n suspension. The u l t r a - f i l t e r e d water behaves i n t h e same manner,

The seale'd t u b e s o b t a i n e d by t h e two methods a r e s u b j e c t e d t o f r e e z i n g under the Same c o n d i t i o n s a s a

t e s t tube c o n t a i n i n g o r d i n a r y d i s t i l l e d w a t e r , The mean spontaneous f r e e z i n g Leniperature of t h e l a t t e r i s -10,6°,

T e s t no, 1: u l t r a - f i l t e r e d water: