368 PROCEEDINGS OF THE AMERICAN ACADEMY. 



until free from chlorine. Two distillations were invariably sufficient 

 to accomplish this end, if the first third of each distillate was rejected. 



Silver. — Pure silver was obtained by methods already many times 

 employed in this laboratory. Silver nitrate was dissolved in a large 

 volume of water and the silver was precipitated as chloride with an 

 excess of hydrochloric acid. The precipitate was thoroughly washed 

 and reduced with alkaline invert sugar. The reduced silver, after 

 being washed, was dried and fused on charcoal in the flame of a clean 

 blast lamp. After the buttons had been cleaned by scrubbing with sand 

 and etching with nitric acid, they were dissolved in pure dilute nitric 

 acid and the silver was precipitated as metal with ammonium for- 

 mate.^^ This silver was washed and fused in the flame of a blast lamp 

 on a crucible of the purest lime. The buttons were cleaned as before, 

 and then electrolyzed.^^ Finally the electrolytic crystals were fused 

 in a boat of the purest lime in a porcelain tube in a current of pure 

 electrolytic hydrogen, i* The bars of silver were cut in pieces with a 

 fine steel saw, etched with dilute nitric acid until fr'ee from iron, washed, 

 dried, and heated in a vacuum to 400°C. The silver was kept in a 

 desiccator containing solid potassium hydroxide. 



Lead chloride. — Three samples of lead chloride from two entirely 

 different sources were employed. Sample A was prepared from me- 

 tallic lead. Commercial lead was dissolved in dilute nitric acid, and 

 the solution, after filtration, was precipitated with a slight excess of 

 sulphuric acid. The lead sulphate was thoroughly washed, suspended 

 in water, and hydrogen sulphide was passed in until the sulphate was 

 almost completely converted into sulphide. Next the sulphide was 

 washed with water, dissolved in hot dilute nitric acid, and the solution 

 was freed from sulphur and unchanged sulphate by filtration. The 

 lead nitrate thus obtained was crystallized twice, dissolved in water, 

 and precipitated in glass vessels with a slight excess of hydrochloric 

 acid. The chloride was washed several times with cold water and then 

 crystallized from hot water eight times, the last five crystallizations 

 being carried out wholly in platinum, with centrifugal drainage after 

 each crystallization. In crystallizing the lead chloride the whole sam- 

 ple was not dissolved at one time, but the same mother liquor was used 

 for dissolving several portions of the original salt. Needless to say, 

 the chloride was not exposed to contact with the products of combus- 

 tion of illuminating gas, lest lead sulphate be formed. 



Sample B was prepared from commercial lead nitrate. This salt was 



12 Richards and Wells, Pub. Car. Inst., No. 28, 19 (1905). 

 W Abraliall, Jour. Chem. Soc. Proc, 1892, p. CGO. 

 " Baxter, These Proceedings, 39, 249 (1903). 



