THE ANALYSIS OF SILVER BICHROMATE. 1 63 



The preceding table gives the results of all the final experiments in the order 

 in which they were carried out. The preliminary analyses, which were de- 

 fective in various ways, are not recorded. 



DISCUSSION OF RESULTS. 



The results of the foregoing experiments are as concordant as one can rea- 

 sonably expect, since the insoluble silver salts are in general difficult to obtain 

 definite in composition.* The extreme values differ by only o.oi per cent, 

 while the averages of the different samples show an extreme difference of less 

 than 0.005 P^r cent. The composition of the dichromate is evidently not affected 

 by the concentration of the nitric acid from which it is crystallized, since the 

 averages from the different samples do not vary regularly with the concen- 

 tration of the nitric acid, the average result obtained from Sample II being 

 lower than that of either Sample I or Sample III. 



If the per cent of silver in silver dichromate is 49.9692, the molecular weight 

 of silver chromate may be calculated from the atomic weight of silver, and 

 from the molecular weight of the chromate the atomic weight of chromium by 

 difference. These calculations have been made with two values for the atomic 

 weight of silver, oxygen being assumed to have the value 16.000, It is to be 

 noted that the percentage error in the determination of the molecular weight 

 of silver dichromate is multiphed four times in the atomic weight of chromium. 



If Ag = 107.880 Ag2Cr207 = 431.786 and Cr = 52.013 

 If Ag = 107.870 Ag2Cr207 = 431.746 and Cr = 52.003 



In the following table are given the results of the preceding research upon 

 silver chromate by Baxter, Mueller, and Hines, together with the average of 

 their values and those presented in this paper: 



Baxter, Mueller, and Hines. Average. 



If Ag = 107.880 Cr = 52.008 52.011 



If Ag = 107.870 Cr = 51.997 52.000 



The agreement of the two independently determined values is highly satis- 

 factory, no matter which value for the atomic weight of silver is assumed, al- 

 though the higher values for silver give slightly better agreement. 



The atomic weights of both chromium and silver may be calculated indepen- 

 dently of any assumption except the atomic weight of oxygen from the fol- 

 lowing equations: 



2Ag + a + 64 = °'^50333 2Ag + la + 112 = ^-^^QeQ^ 



to be 52.074 and 107.941 respectively. However interesting these results may 

 be, they have little real significance, since an error of 0.005 P^^ cent in either 

 ratio causes an error of over o.i unit in the atomic weights of both silver and 

 chromium. 



* Baxter and Coffin: Proc. Amer. Acad., 44, 179 (1909); Jour. Amer. Chem. Soc.,31, 297; 

 Zeit. anorg. Chem., 62, 50. See also preceding paper. 



