OF ARTS AND SCIENCES. 85 



The analyses correspond to the formula 



6 M0O3 . 3 AsoOg . 2 MnO + 6 aq, 



1708 100.00 



The molybdic oxide was determined by diflfereuce only. By mixing 

 a solution of the gummy arsenoso-molybdate of ammonium with solu- 

 tions of zincous and cupric suljDhates respectively, after standing, beau- 

 tiful octahedral crystals were deposited, which in the case of the zinc 

 salt were colorless, in that of copper, of a fine green. The corre- 

 sponding nickel salt was also in beautiful green octahedral crystals. 

 In the zinc salt, 



0.2378 gr. gave 34.52 p;^ As^O, by titrition with iodine. 

 0.3115 gr. '^ 34.47^ " " " 



0.2169 gr. " 34.56r^ " '^ " 



The formula 



6 MoO. . 3 AsoO, . 2 ZnO + 6 aq 



requires 34.38%. In the copper salt, 



0.2619 gr. gave 34.67 <^ AsoOj by titrition with iodine. 

 0.2006 gr. " 34.89% " « 



The formula 



6 MoO^ . 3 AS3O3 . 2 CuO + 6 aq 



requires 34.41%. 



In the cases of both the zinc and copper salts a trace of free arsenous 

 oxide was probably mixed with the salt analyzed. The nickel salt 

 doubtless corresponds to the other three. In the case of the man- 

 ganese salt, fumes of arsenous oxide were given off at very low 

 temperatures. The pale canary-yellow manganese salt obtained by 

 precipitating the 12:5 amnionic salts with manganous sulphate cor- 

 responded to the formula 



