12 ATOMIC WEIGHT DETERMINATIONS. 



cannot be prepared free from oxy-chloride, and that its Sb 

 and CI contents correspond to Sb = 120. Metallic Sb was 

 prepared by reduction of sodic antimoniate, or of oxide, 

 with potassic cyanide, or by Liebig's method. In all cases 

 it was fused for several hours under its own oxide. The 

 haloid salts were purified by fractional recrystallization and 

 distillation, in part in a current of carbon di-oxide. {Proe. 

 Am. Acad., 13, 1877, 1.) 



ARSENIC. 



The specific heat of metallic arsenic, as determined by 

 Regnault, and the vapor density of a number of volatile 

 compounds, as determined by Dumas, Mitscherlich, Bunsen, 

 and others, prove that the atomic weight of this element 

 must be in the neighborhood of 75. {Gmeliii- Kraut, I. c; 

 and L. Meyer, I. c.) 



J. J. Berzelius: 75.1 (0 = 16); 469.4 (0 = 100). 



2.203 grammes of arsenious acid, heated with sulphur in 

 a distilling apparatus in such a manner that sulphurous 

 acid, but no sulphur, could escape, set free 1.069 grammes 

 sulphurous acid. If S = 200.75, the value follows. {Pog- 

 gend. Ann., 8, 1826, 22; and Lehrbuch, 5 ed., 3, 1205.) 



J. Dumas : 75 {O = 16). 



Dumas found the vapor density of arsine 2.695. [This 

 value multiplied by 28.94278 gives As = (sensibly) 75.] 

 {Ann. de Chim. et de Phys., 33, 1826, 337.) 



J. Pelouze: 75 (O = 16); 468.75 (O = 100). 



A known weight of arsenic ter-chloride was introduced 

 into a nitric acid solution of a known weight of perfectly 

 pure silver, the chloride being in slight excess. The excess 

 of chloride was then titrated with decimal silver solution.* 

 As the mean of three experiments Pelouze found As = 

 937.50; extreme difference, 0.8. Ag = 1349.01; CI = 

 443.2. The ter-chloride was repeatedly distilled to free it 

 from excess of chlorine. It was colorless, dissolved com- 



* This method, which has heen frequently emploj'cd in the determination 

 of atomic weights, will be referred to as " Pelouze's method." 



