BAXTER AND CHAPIN. — ATOMIC WEIGHT OF NEODYMIUM. 233 



did not confirm this statement, for in several instances salt which ap- 

 parently had been very completely dried, after fusion in a current of 

 hydrochloric acid gas was found to contain a considerable amount of 

 basic salt. Since, however, material which had been dried at temper- 

 atures slightly below the melting point of the anhydrous salt gave 

 absolutely clear solutions, the expedient was adopted of drying the 

 salt for analysis as completely as possible without fusion, with the 

 expectation of determining the water in subsequent experiments. 

 During later experiments for determining the residual water it was 

 found that the preliminary drying had not been effective in the earlier 

 experiments, and that salt which has been dried as for analysis and 

 then fused in a current of hydrochloric acid gas does give a perfectly 

 clear solution. This information was unfortunately acquired too late 

 to be of direct use in preparing the salt for analysis. Since, however, 

 the dried but unfused salt was found to contain a constant very small 

 proportion of moisture, and since a correction was applied for this mois- 

 ture, no appreciable error could have been introduced by the incomplete 

 drying. It is hoped, nevertheless, before long to institute further an- 

 alyses with material which has been fused. 



The apparatus employed in the drying of the neodymium chloride 

 was essentially that used by numerous investigators in this laboratory 

 for the dehydration of chlorides. Hydrochloric acid gas was generated 

 by the action of concentrated sulphuric acid upon concentrated hydro- 

 chloric acid, and was dried by passage through five towers about thirty 

 centimeters long and four centimeters in diameter filled with glass 

 beads moistened with concentrated sulphuric acid. Nitrogen was pre- 

 pared by Wanklyn's method of passing air through concentrated am- 

 monia solution and then over hot copper. The excess of ammonia 

 was removed and the nitrogen was purified and dried by passing over 

 dilute sulphuric acid, silver nitrate solution, solid caustic potash, con- 

 centrated sulphuric acid, and resublimed phosphorus pentoxide. Ni- 

 trogen prepared in this way always contains hydrogen,^ produced by 

 the catalytic decomposition of the excess of ammonia in passing over 

 the hot copper, in quantities which vary with the excess of ammonia, 

 the temperature of the copper, as well as the length of the copper layer 

 and the speed of the gases. The hydrogen could not have had any 

 effect upon the neodymium chloride, however, and is an advantage in 

 preventing the attacking of the platinum boat. Air was purified and 

 dried by reagents similar to those used in the purification of the nitro- 

 gen. The hydrochloric acid apparatus was constructed wholly of glass, 



^ Our attention was first called to this fact by Dr. R. C. Wells. 



