362 



Frederick Guthrie on Salt Solutions 



The determination at 0° C. was made by estimating the 

 chlorine as chloride of silver. There is such little difference 

 between the composition of the cryohydrate and the hydrate 

 separated at 0°, that I have been unable to estimate the com- 

 position at intermediate temperatures. There is no evidence 

 of the formation of any other hydrate than the one usually 

 regarded as containing six molecules of water. On account 

 of the difficulty of exactly measuring such low temperatures as 

 are here concerned at the maximum, I have less confidence in 

 the exactness of the form of the tracing of this salt than of any 

 other. 



§ 131. Separation of Ice from a solution of Hydrochloric 

 Acid. — Although I have made a separate study of the hydrogen 

 salts of several of the acids, I may here adduce one instance, 

 namely that of hydrochloric acid, in order especially to com- 

 pare the forms of the temperature-curve of a body which is, as 

 far as we know, without a cryohydrate *, with the curve-forms 

 of metallic salts, all of which have cryohydrates within the 

 range of artificial cold. 



By a silver determination I found that 3*2726 grms. of a 

 pure acid contained 1 grm. of HC1 and 2*7734 grms. of water. 

 From this acids of unit percentage weights were formed. 



Table XX. 



HCl 



per cent, by 



H 2 



per cent, by 



Greatest 

 cold as 



Temperature 

 at which soli- 

 dification 



Nature of 

 solid. 



weight. 



weight. 



cryogen. 



begins. 





1 



99 



o 



-8-7 



Ice. 



2 



98 





- 20 



tf 



3 



97 



-20 



- 3-6 



>> 



4 



96 





- 5-3 



it 



5 



95 



-2-6 



- 70 



it 



6 



94 





- 9 





7 



93 



'-4*0 



-115 



n 



8 



92 





-140 



a 



9 



91 



l"i-6 



-17 





10 



90 



-49 



-20 5 



a 



12 



88 



-6-2 



-270 



ii 



14 



86 



-76 



-350 



ii 



16 



84 



-8-0 



-450 



ii 



The tracing of these values is shown on fig. 1, and may 

 be compared with that of spirit of wine derived from the 

 numbers given in § 96, Table XI. In neither tracing is there 

 any decided indication of contrariflexure, although the spirit- 



* A cryohydrate of HCl has recently been described by a French 

 chemist. 



