80 MOLECULAR WEIGHT OF ARGENTIC SULPHATE, ETC. 



before making a weighing and during this time was covered by a black 

 cloth to protect the sensitive salts from the light. 



In order to correct the weights to the vacuum standard, the specific 

 gravity of argentic sulphate is needed. Following are the published results 

 concerning this datum: 



Density of Argentic Sulphate. 



5.341. Karsten, Schweigger's J., 65, 419 (1832). 



5.322. Playfair and Joule, Mem. Chem. Soc., 2, 430 (1845). 



5.410. Filhol, Ann. Chim. et Phys. [3], 21, 417 (1847). 



5.425. Schroder, Pogg. Ann., 106, 245 (1859). 



5*54'} Petterson, Upsala, Nova Acta [3], 9, 35 (1874). 



After a study of the original papers, the value 5.45 was provisionally 

 adopted as the most probable value; but, as there was some doubt about 

 its accuracy, this was verified by experiment. 



The density of the toluol to be displaced by the salt was determined by 

 means of an Ostwald pycnometer at 29.2 to be 0.8566 (the mean of 3 

 concordant determinations) ; 6.067 grams of previously fused silver sul- 

 phate were found to displace 0.9532 gram of this toluol, and therefore 

 occupied 1.113 ml. (the mean of two determinations). Hence the density of 

 argentic sulphate is 5.45, as supposed. This involves an additive correc- 

 tion of 0.0000775 gram to each apparent gram of the salt, a value which 

 is decreased 0.0000011 by an increase of a centimeter of atmospheric 

 pressure, or decreased 0.00000026 by an increase of a degree of tempera- 

 ture. The correction to the weight was applied accordingly. 



THE CONVERSION OF ARGENTIC SULPHATE INTO CHLORIDE. 



The next step in the process was the conversion of the carefully 

 weighed fused sulphate into chloride by heating it in a current of dry 

 hydrochloric acid gas. This reaction has been observed by Hensgen. 1 



The hydrochloric acid generator used for the previous work was con- 

 structed entirely out of glass. Pure ammonic chloride or concentrated 

 hydrochloric acid was placed in the flask (/) shown in figure 4, and con- 

 centrated sulphuric acid was dropped upon it slowly. The gas was dried by 

 passing through the tower (/) containing beads moistened with concen- 



1 Hensgen, Recueil des Travaux chimiques de Pays-Bas., 2, 124 (1883). "Le 

 sulfate d' argent absorba 2 mol. HC1 a la temperature ordinaire, avec un degagement 

 de chaleur notable, et se changea completement en chlorure. En chauffant, meme 

 jusqu a 300, la reaction inverse (observee par M. H. avec le sulfate de cuivre) n'eut 

 point lieu, mais 1'acide sulphurique fut chasse completement par un courant d'air. 

 Parmi les sels susdits, le sulfate d'argent est celui qui d' apres les donnees thermi- 

 ques, doit se changer en chlorure avec le plus grand degagement de chaleur." (See 

 p. 83.) 



