218 



Frederick Guthrie on Salt Solutions 



As a cryogen the glycerine behaves as hydrochloric acid and 

 other liquid elements of cryogens ; namely, the temperature ob- 

 tained is lower if the liquid be previously cooled. 



§ 160. Tartaric Acid. — As a cryogen, tartaric acid gives 

 the temperature — 13°*5. I cannot say that I have cleared up 

 all the ambiguities in the behaviour of this body. The sepa- 

 ration of ice took place with regularity as far as the following 

 solutions are concerned. 



C 4 H G 6 per 

 cen by weight. 



H 2 O per cent, 

 by weight. 



Temperature at 

 which ice sepa- 

 rates. 



5 



95 



o 



- 07 



10 



90 



- 1-4 



15 



85 



- 2 5 



20 



80 



- 3 7 



25 



75 



- 47 



30 



70 



- 6-3 



35 



65 



- 76 



40 



60 



-101 



45 



55 



-13 



Apparently continuous with these results is the separation 

 of a solid at — 16°*5 from a 50-per-cent. and of a solid at 

 — 17°*6 from a 55-per-cent. solution. But there is here really 

 a breach of continuity. The 55-per-cent. gives up tartaric 

 acid at —17° when crystals of that body are introduced. And 

 it is difficult to say whether ice, or acid, or a cryohydrate is 

 separated from the 50-per-cent. at — 16°*5. If a 50-per-cent. 

 solution be cooled to —19° and a smaller portion of the same 

 solution which has been solidified by an ether-carbonic-acid 

 cryogen be introduced into the first, the temperature rises to 

 — 8°, and opaque crystals are formed, while that temperature 

 is constantly maintained. The same body at the same tem- 

 perature is formed even when the first solution has only been 

 cooled to —14°. I think, therefore, that there is with tar- 

 taric acid a body similar to that which w r e encountered with 

 the iodide of sodium, namely a subcryohydrate. Owing to the 

 sirupy nature of these strong solutions at these low tempera- 

 tures, and the very slow rate at which the separation of their 

 constituents ensues, I do not think that analyses of such inter- 

 mediate subcryohydrates would be sufficiently trustworthy for 

 reproduction. But the cryohydrate which separates at —8° 

 is distinct enough. 



4*0735 grms. of solution gave 1*8972 grm. of C 4 H 6 6 , or 

 46*6 per cent. 



A solution kept for two days and nights at 0° showed the 



