76 MOLECULAR WEIGHT OF ARGENTIC SULPHATE, ETC. 



portion of the tube (A) ; by pulling this the tube could be readily rotated. 

 It was hung on the balance in a horizontal position by means of a platinum 

 wire. The same tube was used throughout the research, the cylindrical 

 shape giving it sufficient strength to withstand all the strains to which it 

 was subjected. 



The tube remained remarkably constant in weight in spite of the very 

 vigorous treatment it received. During the entire fifteen experiments the 

 loss in weight was only 0.41 mg., and during the twelve experiments of 

 the final series the loss was only 0.16 mg. This slight loss is probably 

 .accounted for by a slight solubility of the quartz in the concentrated 

 ammonia or potassic cyanide solution used to remove the argentic chloride 

 after each determination. 



The sulphate of silver prepared as described above must have contained 

 a little included water and excess of sulphuric acid, since it had been crys- 

 tallized from an acid solution. 1 The only certain method of removing 

 mother liquor included within crystals is to fuse the salt. This part of the 

 problem caused considerable difficulty ; for it was found that argentic sul- 

 phate decomposes slightly when fused in air, becoming yellowish-brown 

 in color. In order to decrease this thermal dissociation, the experiment 

 was made of fusing the salt in a current of dilute sulphuric oxide, with 

 complete success. The salt is then pure white in color. 



The small crystals of argentic sulphate were pushed into the tube with 

 a platinum rod, and the narrow ends were freed from loosely adhering 

 argentic sulphate by means of a clean feather tip, which had been previously 

 washed with alcohol and ether to free it from grease. The tube was sup- 

 ported, on hooks of hard glass, in front of the apparatus for delivering 

 sulphur trioxide. The very fine platinum wire needed for rotating it had 

 been wound around the tube in the first place. 



The apparatus for delivering a current of pure dry air or sulphur tri- 

 oxide or hydric chloride is shown diagramatically in figure 4. A cur- 

 rent of air was first driven over red-hot copper oxide (A) to remove or- 

 ganic matter, and subsequently through an Emmerling tower (B) con- 

 taining beads moistened with a strong caustic potash solution. This tower 

 was closed by a rubber stopper at the top, which introduced no impurity, 

 since nothing but pure air passed over it. From this point, however, the 

 apparatus contained no rubber connections or stoppers. All stopcocks 

 were lubricated with phosphoric or sulphuric acid. 



The air was dried by passing through two Emmerling towers (C and D) 

 containing beads moistened with concentrated sulphuric acid. The cur- 



1 Richards, Proc. Amer. Phil. Soc., 42, 28 (1903). 



