baxter and stewart. — praseodymium chloride. 189 



The Method of Analysis. 



After the salt had been fused and weighed, the boat was transferred 

 to a glass-stoppered Erlenmeyer flask and treated with about 500 ee. 

 of pure water. In eleven of the analyses the salt dissolved immedi- 

 ately leaving an absolutely clear solution. In the remainder of the 

 analyses, after the bulk of the salt was in solution, by close inspection 

 a small quantity of the insoluble basic chloride could be seen. On 

 allowing the flask to stand for a considerable period, 24 to 48 hours 

 in general, this basic salt disappeared, and in a few instances gentle 

 heating was used to accelerate its solution. When the solution was 

 clear, it was transferred quantitatively to the 3 or 4 liter glass-stop- 

 pered Erlenmeyer precipitating flask. The rinsings of the weighing 

 bottle were added and the solution diluted to a volume of from 1200 

 to 1500 cc. In the mean time a quantity of pure silver as nearly as 

 possible equivalent to the praseodymium chloride was dissolved in 

 nitric acid, in a dissolving flask provided with a column of bulbs to 

 prevent loss by spattering while the metal was dissolving. After 

 diluting the solution of silver nitrate, it was heated to eliminate nitrous 

 acid, and then further diluted to about the same volume as the praseo- 

 dymium chloride solution. The silver nitrate solution was poured 

 into the chloride solution, both being cold, in small portions with con- 

 tinual gentle agitation. When the silver nitrate had been completely 

 transferred to the precipitating flask, the flask was stoppered and 

 gently shaken to insure thorough mixing, and allowed to stand for 

 several days with occasional shaking. Then.it was cooled with ice- 

 water in order to lower the solubility of the silver chloride, and after 

 standing for a day in the ice-bath, portions of the mother liquor were 

 tested for excess of silver or chloride by adding to separate portions 

 equal amounts of 0.01 normal chloride and silver solutions and com- 

 paring the opalescences in a nephelometer. If a deficiency of either 

 chloride or silver was found, this deficiency was made up by adding 

 0.01 normal silver or chloride solution. The amount of either added, 

 expressed in the silver equivalent, is given in the tables of results under 

 the heading "Silver added or subtracted." When equilibrium had 

 been reached, 0.05 gm. of dissolved silver nitrate for each liter of super- 

 natant liquid was added to render the silver chloride less soluble. 

 After the solution had been allowed to stand for at least a day, usually 

 much longer, at room temperature, the precipitate was washed many 

 times by decantation with a solution containing 0.05 gm. of silver 

 nitrate per liter, and several times with ice-cold water, and transferred 

 with cold water to a large weighed platinum-sponge Gooch crucible. 



