74 Conductivity of Aqueous Solutions. Part IV. 



The barium nitrate used was crystallized once from hot water and 

 carefully dried in a current of dry air at 130. The solutions were made up 

 by weighing out the theoretical quantities. It was proved that a portion 

 of salt (3 grams) lost in weight scarcely appreciably (less than 0.5 mg.) 

 on heating for 3^4 hours at 280 to 300 in a platinum dish. 



The magnesium sulphate was recrystallized from hot water and redis- 

 solved without drying in conductivity water to form a stock solution. This 

 solution was analyzed separately for magnesium by precipitating it as 

 magnesium ammonium phosphate and for sulphate by precipitating it as 

 barium sulphate. The content in 1,000 grams of solution expressed in 

 milli-equivalents (1 milli-equivalent = 60.21 mg. MgS0 4 ) was found to 

 be as follows : 



From magnesium determination 344.9 



From sulphate determination 345.1 



From sulphate determination 344.6 



Average 344 . 9 



The solutions of all these substances were made up by weighing out 

 the dry salt, or the stock solution in the case of magnesium sulphate, trans- 

 ferring to a graduated flask, and adding conductivity water enough to 

 bring the solution to the graduation mark at some known temperature 

 between 15 and 25. The concentration of the salt was then calculated 

 over to 4 on the assumption that the solution had the same expansion- 

 coefficient as pure water. 



34. SYSTEMATIC ERRORS AND THEIR ELIMINATION. 

 VOLATILIZATION OF THE SOLVENT. 



The vapor space in the bomb at the temperatures 100, 156, and 218 

 was not sufficiently large to cause an error of 0.1 per cent ; and no correc- 

 tion was applied at these temperatures. However, at 281 and 306, it 

 was necessary to apply a correction, which varied with the amount of 

 liquid in the bomb. The vapor-space correction at 281 was determined 

 experimentally by measuring the conductance when two different quanti- 

 ties of a 0.01 normal sodium chloride solution were introduced. 



The results were as follows : 



