ARSENIC. 215 



The determinations made by Hibbs* are based upon an altogether 

 different process from any of the preceding measurements. Sodium 

 pyroarsenate was heated in gaseous hydrochloric acid, yielding sodium 

 chloride. The latter was perfectly white, completely soluble in water, 

 unfused, and absolutely free from arsenic. The vacuum weights are 

 subjoined, with a column giving the percentage of chloride obtained 

 from the pyroarsenate. 



Na^As^O^. NaCl. Percentage. 



.02177 - OI 439 66. 100 



.04713 .03"5 ' 66.094 



.05795 .03830 66.091 



.40801 .26981 66.128 



.50466 -33345 66.092 



.77538 .51249 66.095 



.82897 .54791 66.095 



1.19124 .78731 66.092 



1.67545 1.10732 66.091 



3.22637 2.13267 66. 101 



Mean, 66.098, .0030 



Hence As = 74.340, .0235. 



In the calculation of the foregoing values for arsenic, the subjoined 

 atomic weights have been assumed : 



O ---- 15.879, .0003 K = 38.817, .0051 



Ag 107.108, db .0031 Na = 22.881, .0046 



Cl =. 35.179, zb .0048 S = 31.828, ib. ooi 5 



Br = 79.344, -0062 Cr = 51.742, .0034 



To the single determination by Berzelius we may arbitrarily assign a 

 weight equal to that of the result from Wallace's bromide series. The 

 general combination is then as follows : 



From Berzelius' experiment As = 74.460, .0436 



" = 74.45> . OI 9 



" = 73.668, .0436 



From As 2 O 3 (Kessler) " = 74.607, .0175 



From Na 4 As 2 O 7 " = 74.340, db .0235 



General mean As 74.440, .0106 



If O = 16, As = 75.007. 



* Doctoral thesis, University of Pennsylvania, 1896. Work done under the direction of Professor 

 E. F. Smith. In the fifth experiment the weight of NaCl is printed .33045. This is evidently a 

 misprint, which I have corrected by comparison with the other data. The rejection of this ex- 

 periment would not affect the final result appreciably. 



