184 PROCEEDINGS OF THE AMERICAN ACADEMY. 



the surface of the tube where it came in contact with the salt. Experi- 

 ence showed, however, that with careful management the attacking of 

 the quartz could be wholly prevented. The vessel used to contain the 

 arsenate was a quartz tube nearly two centimeters in diameter but 

 joined to small tubes at each end. These tubes were exactly like those 

 employed by Richards and Jones in the conversion of silver sulphate 

 into silver chloride. 7 After the tube had been weighed by substitution 

 for a counterpoise similar in shape and size, a suitable quantity of 

 silver arsenate was introduced, and the tube and contents were heated 

 in a current of pure dry air for between seven and eight hours at 250° C. 

 Although this treatment is not sufficient to expel last traces of moisture, 

 it was hoped that by uniform treatment of the arsenate in all the 

 analyses the proportion of water retained by the salt could be reduced 

 to a constant percentage, which could be determined in separate ex- 

 periments. The complete drying of the salt by fusion was not permis- 

 sible because of decomposition of the arsenate at temperatures in the 

 neighborhood of its fusing point. During the drying of the arsenate 

 the quartz tube was surrounded with a cylinder of thin platinum foil and 

 was contained in a hard glass tube connected with an apparatus for 

 furnishing a current of pure dry air. The hard glass tube was heated 

 by means of two aluminum blocks 15 centimeters by 13 centimeters by 

 5 centimeters, one placed above the other, the upper surface of the 

 lower block and the lower surface of the upper being suitably grooved 

 to contain the tube. The blocks were bored to contain a thermometer 

 the bulb of which was located near the middle of the tube. This oven 

 could be readily maintained at constant temperature within a very 

 few degrees by means of a small Bunsen flame. We are indebted to 

 Dr. Arthur Stahler of the University of Berlin for the suggestion of this 

 method of heating. In order to purify and dry the air it was passed 

 through a tower filled with beads moistened with dilute silver nitrate 

 solution, through a tower filled with small lumps of solid potassium 

 hydroxide, then through three towers filled with beads moistened with 

 concentrated sulphuric acid, and finally through a tube filled with 

 resublimed phosphorus pentoxide. The apparatus was constructed 

 wholly of glass, with ground joints. 



After being heated, the quartz tube was transferred to a desiccator 

 and allowed to come to the temperature of the balance case before 

 being weighed. The quartz tube was then placed upon hard glass 

 supports, in a horizontal position, one end being slipped into a larger 

 tube through which could be passed a current of either dry hydro- 



7 Pub. Carnegie Institution, No. 69, 69 (1907). 



