BAXTER AND CHAPIN. — ATOMIC WEIGHT OF NEODYMIUM. 235 



The Method of Analysis. 



In order to dissolve the chloride the boat was first transferred to a 

 large dry Erlenmeyer flask, a column of bulbs was inserted in the neck 

 of the flask and enough water to cover the boat was introduced through 

 the bulbs. These precautions were taken because of the violence of the 

 action of the water upon the finely divided anhydrous salt, in order to 

 avoid both mechanical loss of material and possible evaporation of 

 hydrochloric acid owing to hydrolysis at the high temperature which re- 

 sults at the moment when the salt comes in contact with water. That 

 this error is not a serious one is evident from the fact that although in 

 the first five analyses the use of the column of bulbs was omitted, yet 

 the results of these analyses are not markedly diff"erent from the others. 

 The solution was allowed to stand in the flask for some time in order to 

 ensure absorption of any volatilized hydrochloric acid. Every specimen 

 of salt dried and dissolved in this way gave a perfectly clear solution. 



The solution of the neodymium chloride was diluted to a volume of 

 about one liter with water containing a small amount of nitric acid. 

 Then an equally dilute solution of a very nearly equivalent amount of 

 pure silver nitrate containing nitric acid was added to the solution of 

 the chloride. The glass-stoppered precipitating flask containing the 

 solution was thoroughly shaken and allowed to stand for about twenty- 

 four hours, and then an excess of silver nitrate of about one tenth 

 of a gram was added to complete the precipitation. 



After standing until the supernatant liquid was perfectly clear, the 

 precipitate was thoroughly washed, first with dilute silver nitrate solu- 

 tion and then with very dilute nitric acid in the earlier analyses, with 

 pure water in the later ones, and was collected upon a weighed Gooch- 

 Munroe-Neubauer crucible. Then, after the crucible and contents had 

 been dried in an electric air bath at about 150° for eighteen hours, 

 they were weighed. 



The moisture retained by the dried silver chloride was estimated in 

 each analysis by determining the loss in weight during the fusion of 

 the dried silver chloride in a weighed porcelain crucible. The weight 

 of silver chloride dissolved in the filtrate and silver nitrate wash-waters 

 was assumed to be 0.00003 gram per liter.^ That dissolved in the acid 

 or aqueous washings together with the ammonia rinsings of the precipi- 

 tating flask was determined by comparison with standard solutions in 



1 Richards and Weils, Pub. Car. Inst., No. 28, 30 (1905); Jour. Amor. 

 Chem. Soc, 27, 487. 



