COMPOUNDS THAT HAVE BEEN STUDIED. 29 



The conductivity of the solution as an approximate measure of its disso- 

 ciation. 



The specific gravities of the solutions, in order to calculate the difference 

 between 1,000 grams of water and the amount contained in a liter of the 

 solution. 



In the various tables of data the symbols have the following significance: 



In the tables of freezing-point measurements m is the concentration 

 in terms of gram-molecules per liter; J the observed freezing-point lowering 



corrected for the separation of ice, and the molecular lowering of the 



TTt 



freezing-point. 



In the conductivity tables the symbols have the usual significance; v is 

 the volume of the solution, or the number of liters that contain a gram- 

 molecular weight of the electrolyte; n v is the molecular conductivity; is 

 the approximate dissociation. 



In the refractivity tables TO is the concentration, A is the angle as read, and 

 n is the index of refraction. 



In the specific gravity tables m is the concentration; W So i the weight 

 of 25 cc. of the solution; W Sa it the weight of the salt contained in 25 cc. 

 of the solution; and W H2 o the weight of water contained in 25 cc. of the 

 solution. The percentage correction is the correction that must be applied 

 to the freezing-point lowering, in order to refer it to 1,000 grams of solvent, 

 instead of the amount of water that is present in a liter of the solution in 

 question. 



The symbols in the hydrate tables have the following significance: m is 

 the concentration in terms of gram-molecules per liter; the approximate 



dissociation of the solution; L the theoretical molecular lowering of the 



j 

 freezing-point referred to 1,000 grams of the solvent; the molecular 



lowering found experimentally; L' the corrected molecular lowering; m' the 

 number of gram-molecules of water in combination, both being referred to 

 1,000 grams of water; H the number of molecules of water in combination 

 with one molecule of the salt at the concentration in question, if a liter of 

 the solution, at that concentration, contained 1,000 grams of water. 



In order to ascertain the number of molecules of water actually in com- 

 bination with one molecule of the dissolved substance, at the concentration 

 given, it is only necessary to divide the value of m' for that concentration 

 by the concentration expressed in terms of a gram-molecular weight in 1,000 

 grams of the solvent. The difference between the values of H found by 

 these two methods is generally quite negligible, being smaller than experi- 

 mental errors. It becomes appreciable only when the "correction" per 

 cent is large, i. e., in very concentrated solutions. 



