BAXTER AND STEWART. — PRASEODYMIUM CHLORIDE. 183 



perature of the heptahydrate 19 to be 111 but when the salt is heated 

 in a current of hydrochloric acid gas, the melting point is somewhat 

 lowered. Therefore until a very considerable proportion of the water 

 had been expelled, the temperature was kept below 100°. The 

 temperature was then raised to about 165° where the last molecule of 

 crystal water begins to evaporate, according to Matignon, 20 and when 

 the salt was essentially anhydrous it was gradually heated to about 

 350°. During the latter part of the heating only hydrochloric acid was 

 passed through the tube. The aluminum block oven 21 which had been 

 used for heating the salt up to this point was now replaced by a sleeve 

 which could be heated electrically and the salt was first heated to dull 

 redness for a few minutes and then quickly to its fusing point, which 

 Matignon 22 states to be 818°. 



The platinum boat with the salt was placed in a quartz tube which 

 formed part of the "bottling apparatus" 23 containing the weighing 

 bottle with its stopper in which the boat originally had been weighed, 

 and the bottling apparatus was connected with systems for the pro- 

 duction of pure dry hydrochloric acid, nitrogen, and air. The hy- 

 drochloric acid gas was generated by adding C. P. concentrated 

 sulphuric acid to C. P. fuming hydrochloric acid, and the gas was dried 

 by passing through five towers filled with beads moistened with con- 

 centrated sulphuric acid which had previously been heated nearly to 

 its boiling point. Nitrogen was prepared by Wanklyn's method of 

 saturating air with ammonia and passing the mixture over hot copper 

 gauze. The excess of ammonia was removed by dilute sulphuric acid, 

 and the nitrogen was further purified and dried in towers containing 

 glass beads moistened with silver nitrate solution, fused potassium 

 hydroxide, concentrated sulphuric acid, and phosphorus pentoxide. 

 Nitrogen made in this way invariably contains a small proportion of 

 hydrogen, 24 owing to catalytic decomposition of the excess of ammonia 

 in the copper tube, but this gas would do no harm in the present 

 instance. Air was purified and dried by reagents similar to those used 

 for purifying the nitrogen. The apparatus was constructed wholly of 

 glass with either ground or fused joints, except at the beginning of the 

 air and nitrogen apparatus. By means of stop-cocks any one of the 



19 Matignon found 105°. Loc. cit. 



20 Loc. cit. 



21 Proc. Amer. Acad., 44, 184 (1909); Jour. Amer. Chem. Soc, 31, 206. 



22 Compt. rend., 140, 1340 (1905). 



23 Richards and Parker, Proc. Amer. Acad., 32, 59 (1896). 



24 Dr. R. C. Wells first pointed out this fact. 



