84 



RESEARCHES UPON ATOMIC WEIGHTS. 



0.00030 gm. This correction was confirmed in another experiment in which 

 the hard-glass tube was kept at the highest temperature obtainable with the 

 blast lamp for an hour. The observed gain in weight of the absorption tube 

 was 0.00048 gm. A negative correction of 0.00030 gm. was applied in each water 

 determination. 



In order to allow for moisture the weight of the arsenate was therefore always 

 corrected by subtracting 0.000056 gm. per gram of salt. Ebaugh took no notice 

 of the water contained in silver arsenate which had been dried at only 170°. 



SPECIFIC GRAVITY OF SILVER ARSENATE. 



In order that the apparent weight of the silver arsenate might be corrected 

 to a vacuum standard, the specific gravity of the arsenate was found by deter- 

 mining the weight of toluol displaced by a known quantity of salt. The toluol 

 was first dried by means of stick soda and was then distilled, with rejection of 

 the first portion of the distillate. Its specific gravity at 25° referred to water 

 at 4° was found to be 0.8620. Pains were taken to remove air from the arsenate 

 when covered with toluol by placing the pycnometer in an exhausted desiccator. 



The following vacuum corrections were applied: 



All weighings were made upon a nearly new short-armed Troemner balance, 

 easily sensitive to 0.02 mg. with a load of 50 gm. 



The gold-plated Sartorius weights were several times carefully standardized 

 to hundredths of a milligram by the method described by Richards,^ and were 

 used for no other work. 



* Jour. Amer. Chem., Soc, 22, 144 (1900). 



