452 



Frederick Guthrie on Salt Solutions 



20 and 30 per cent, solid), the following results are obtained 

 in regard to the comparative influences of nitrate of silver and 

 nitrate of ammonium in retaining ice in solution. 



Table XXVII. 



Solution. 



Calculated. 



Found. 



ri.AgNO a «2NH 4 NO a 



20 per cent. J \ " = \ 



it :: :i ;; 



f5. „ =2 



30 per cent. \ 7 2 



Is. „ =J „ 



-4 1 0. 



-4-8 

 -53 

 -55 

 -69 

 -81 

 -8-8 

 -9-2 



-1-3 C. 



-50 



-55 



-58 

 -6-8 

 -80 

 -8-9 

 -91 



The calculated numbers are got under the hypothesis that 

 the influences of the constituents of the mixture are propor- 

 tional to their masses. That is, if there be n grms. of A 

 and m grms. of B, each being a p per cent, solution, and if 

 A alone gives out ice at t-i and B at t 2 , then (t being the tem- 

 perature at which the mixture gives up ice) 



t = t l + -^—(t 2 -t 1 ); 



and the numbers found do not differ from those calculated 

 more than may be attributed to errors of observation. 



§ 145. Separation of Ice from the mixed Sulphate and Nitrate 

 of Ammonium. — Of the 10-per-cent. solution of the sulphate of 

 ammonium 20 grms. were taken ; of the 10-per-cent. solution 

 of the nitrate of ammonium 10 grms. were taken. The mix- 

 ture of these gave up ice at — 3°'2, which is exactly the tem- 

 perature calculated from the above equation, the glaciating 

 points of the two solutions being — 2°'6 and — o°'5 respectively. 

 We may assume therefore, generally, that the temperature of 

 glaciation of a mixture of two salt solutions of the same per- 

 centage strength is a mean between the glaciation-tempera- 

 tures of its constituents, when new salts are not formed. This 

 chapter, however, will require a great amount of further work, 

 especially for those cases where the constituent solutions of 

 the mixture are not of the same strength. 



§ 146. Further examination of Iodide of Sodium. — In con- 

 clusion I am very glad to be able to throw a clear light on 

 the anomalous and exceptional behaviour of the iodide of 

 sodium. From §§ 65, 68, 69, it appears that while as a 

 cryogen this salt gives the temperature — 26°'5, it solidifies 

 as a cryohydrate at —15°. A large quantity of the iodide, 



