and Attached Water. 



43 



turation ; the ice-curve crosses the acid or subcryohydrate- 

 curve, both continuing their courses for an exceptionally long- 

 distance. 



For the solubility at 0° C, a solution saturated above 0° C. 

 was kept at 0° surrounded by ice and placed in an ice-safe for 

 three davs. 



Solution. An S° US Perceilt - Meau ' 



2*0962 gave 1-0755 or 51"30 ) _,-, 9 o~ 

 2-1288 „ 1-0914 „ 51-27 i~ 0iZ0 °- 



Crystallized citric acid when added to water has a consider- 

 able cooling effect. Thus 



110*9 grams of crystallized acid at 20°*5 C, added to 



. . 16°-5 



2°-5; 



89 ,, water at . . 



lowered the temperature to 

 while 



51*5 grains of anhydrous acid cooled to 0° C. and added to 

 48-5 „ water cooled to . 0° 



gave a temperature of . . —6°. 



The chief results may be summarized in the following 

 Table :— . 



Table XL. 

 Citric acid (anhydrous). 



Anhydrous acid, 



Temperature at 

 which solidifi- 



Body formed. 



per cent. 



cation begins. 





10 



o 



- 11 



Ice. 



20 



- 28 





30 



— 5 





40 



- 8-5 





42-62 



- 9-2 



Cryohydrate. 



45 



451)3 

 47-06 



— 113 ^ 



-117 1 

 -122 \ 

 -137 1 

 -15 J 



At these temperatures 

 ordinary hydrate, sub- 



507 

 51-5 



evyohydrate, or even 

 ice may be formed. 



As a cryogen, the lowest temperature attainable is — 9°"3; 

 and this confirms the composition of the cryohydrate which 

 had been deduced synthetically. Neither cooling the acid to 

 0° C. nor cooling tin 4 two separately to —9° C. had any effect 

 upon the temperature ; but, of course, the more nearly the 

 initial temperature is to the final one the less is the quantity 

 of liquid formed. 



