Chemical and Physical Notes 



37 



solutions are to be found in collections of physical tables 

 such as those published by the Smithsonian Institution. 



The following table gives the freezing-points of saturated 

 solutions of a number of salts, as recently determined with 

 the greatest care by L. C. de Coppet 1 , who was the first to 

 prove and to clearly enunciate the relation which exists 

 between the molecular weight of a salt and the freezing-point 

 of its aqueous solution. 



TABLE I. De Coppet 's Results. 



The meaning of this table is that if, for example, we take 

 29-6 grms. of common salt (NaCl) and dissolve it in 100 grms. 

 of water, which will take some little time, and we then expose 

 it to an Antarctic temperature such as 25 C. or 30 C., 

 the temperature of the solution will fall until it reaches 

 2i'85 C., when it will remain stationary while crystals 

 form in the solution. This crystallisation will proceed until 

 the solution has become a white solid enamel-like mass. 

 When it has completely solidified, its temperature will begin 

 to fall again, and will continue to fall until it has reached the 

 temperature of the air, 25 C. or 30 C, as the case may 

 be. The white enamel-like mass is what was called by 

 Guthrie the cryohydrate of chloride of sodium. Although 



1 Zeits. f. Phys. Chem,, vol. xxii. p. 239. 



445229 



