BAXTER AND CUAPIN. 



ATOMIC WEIGHT OF NEODYMIUM. 



237 



if the salt is fused in nitrogen, after being dried, hydrochloric acid is 

 liberated owing to hydrolysis with the residual moisture. Fusion in a 

 current of hydrochloric acid gas is not permissible because of the action 

 of this gas upon the phosphorus pentoxide ^ necessary for the absorp- 

 tion of the water. 



Fortunately neodymium chloride is only very slightly volatile at 

 temperatures not far above its fusing point,^ so that it is possible to 

 estimate the moisture content of the dried salt by fusion in a current 

 of hydrochloric acid gas and determination of the loss in weight. The 

 trace of chloride volatilized during the fusion can then be collected and 

 weighed. 



For these experiments a glass tube is obviously unsuited owing to 

 the action of the hydrochloric acid upon the glass at the fusing point 

 of the chloride and consequent vaporization of alkali chloride into the 

 neodymium chloride as well as into the cooler parts of the tube. Hence 

 in these experiments a quartz tube was substituted for glass. This 

 tube was apparently not attacked by the hydrochloric acid gas during 

 a long series of experiments. 



The exact procedure was as follows : The boat with a maximum 

 charge of neodymium chloride crystals was heated in a current of ni- 

 trogen and hydrochloric acid gases, and was bottled and weighed exactly 

 as in preparing the salt for the chloride analyses. After being weighed 

 the boat was replaced in the quartz tube, and when the air had been 

 completely displaced by hydrochloric acid gas, the tube was electrically 

 heated by means of a removable mica sleeve wound with the resistance 

 wire "Nichrome," until the salt was fused. The boat was then 

 bottled in dry air a second time and reweighed. In nearly every ex- 

 periment a barely visible condensation of concentrated hydrochloric 

 acid solution took place in the cool portion beyond the boat. 



* Baxter and Hines, Jour. Amer. Chem. Soc, 28, 779 (1906). 

 2 Neodymium chloride fuses at 785° and is not volatile at 1000° according 

 to Matignon. Compt. Rend., 133, 289 (1901); 140, 1340 (1905). 



