870 PROCEEDINGS OF THE AMERICAN ACADEMY. 



for two final experiments, portions from each of these samples were 

 mixed and then subjected to three additional crystallizations. This 

 last sample was designated Sample C. 



Method of Analysis. 



The lead chloride contained in a weighed platinum boat was first 

 fused in a current of pure dry hydrochloric acid gas. This gas was 

 generated by dropping concentrated sulphuric acid into concentrated 

 hydrochloric acid, and after being washed with a saturated solution of 

 hydrochloric acid, was passed through five towers filled with beads 

 moistened with fireshly boiled concentrated sulphuric acid, to dry the 

 gas. It has already been shown that phosphorus pentoxide may not 

 be used for this purpose.^^ After the salt had cooled, the hydro- 

 chloric acid was displaced by dry nitrogen, and this in turn by dry air. 

 Nitrogen was prepared by passing air charged with ammonia over red- 

 hot rolls of copper gauze, the excess of ammonia being removed by means 

 of dilute sulphuric acid. The gas was passed over beads moistened 

 with a dilute silver nitrate solution and over solid caustic potash to 

 remove sulphur compounds and carbon dioxide respectively, and was 

 finally dried by concentrated sulphuric acid and phosphorus pentoxide. 

 The air was purified and dried in a similar fashion. The apparatus 

 for generating the hydrochloric acid and for purifying the hydrochloric 

 acid and nitrogen was constructed wholly of glass with ground-glass 

 joints. The platinum boat containing the fused chloride was next 

 transferred to a weighing bottle without exposure to moist air, by 

 means of the bottling apparatus, which has frequently served for a 

 similar purpose in many atomic weight investigations in this labora- 

 tory. 17 After standing some time in a desiccator in the balance room, 

 the weighing bottle was weighed. In most of the analyses the lead 

 chloride was dissolved from the boat by prolonged contact with boil- 

 ing water in a Jena glass flask. In the last two analyses, in order 

 to show that no error was introduced through solubility of the glass, 

 the solution was prepared in a large platinum retort, and was not 

 transferreil to the precipitating flask until cold. 



Very nearly the necessary amount of pure silver was then weighed 

 out and dissolved in redistilled nitric acid diluted with an equal 

 volume of water in a flask provided with a column of bulbs to pre- 

 vent loss by spattering. After the silver was all dissolved, an equal 

 volume of water was added, and the nitrous fumes were expelled 



" Baxter and Hincs, Jour. Amer. Chem. Soc, 28, 779 (1906). 

 " Richards and Parker, These Proceedings, 32, 59 (1896). 



