BAXTER AND CIIAPIN. — ATOMIC WEIGHT OF NEODYMIUM, 231 



crystallized, with centrifugal drainage in platinum Gooch crucibles ^ in 

 each case. The crystal yield was brought to a maximum by treating 

 the solutions at 0° with hydrochloric acid gas obtained by warming 

 concentrated solutions of the acid and led to the solutions through a 

 quartz tube. Drying over sulphuric acid in a vacuum desiccator and 

 powdering in an agate mortar completed the preparation for the final 

 dehydration and analysis. 



On account of the small quantity of material in each fraction of the 

 final series, adjacent fractions were combined. The combinations actu- 

 ally analysed were 2923-2924, 2926-2927-2928, 2932-2933, and 2936- 

 2937. A suspicion of contamination by platiimm during the ignition 

 of the oxides in platinum led to a slight change in the purification of 

 these fractions. The original oxide was dissolved in hydrochloric acid 

 in a quartz dish, and hydrogen sulphide, generated by the action of 

 sulphuric acid on ferrous sulphide and thoroughly scrubbed with water, 

 was passed into the hot, slightly acid solution. A slight black precipi- 

 tate of platinum sulphide was formed in every case. The oxalate was 

 precipitated from the filtered and boiled solution, and was collected 

 and dried as before. In the ignition of this oxalate an electrically 

 heated quartz muffle, kindly loaned to us by Dr. H. H. Willard, was used. 

 Since the temperature of the muffle was very uniform, a lower tempera- 

 ture could be employed for the decomposition of the oxalate. The 

 product of decomposition, which contained a large proportion of car- 

 bonate when obtained in this way, was dissolved in hydrochloric acid 

 in a quartz dish and was crystallized as before. The first mother 

 liquor, which in the case of fractions 1302 and 1614 had been slightly 

 tinged with yellow, was in the case of all the other fractions free from 

 such evidence of dissolved platinum. 



The Preparation of Pure Silver. 



Pure silver was prepared by methods which have already been found 

 to be very effective. Since these methods have been described in 

 detail several times in papers from this laboratory,^ only a brief outline 

 of the processes is given here. Crude silver was dissolved in nitric 

 acid, precipitated as chloride, reduced with alkaline invert sugar, and 

 fused on charcoal. After cleansing by scrubbing with sand and etching 

 with nitric acid, the buttons were again dissolved in nitric acid and 

 the metal was precipitated from solution with ammonium formate. The 



1 Baxter, Jour. Amer. Chem. Soc, 30, 286 (1908). 



2 See especially Richards and Wells, Pub. Car. Inst., No. 28, 16 (1905); 

 Jour. Amer. Chem. Soc, 27, 472. 



