OF ARTS AND SCIENCES. 211 



with acetate of lead, thereby obtaining a green solution of acetate of 

 chromic oxide and a yellow precipitate of chromate of lead ; he treated 

 the same substance with arsenic acid, and obtained the insoluble arse- 

 niate of chromic oxide and chromic acid in solution. By washing the 

 original precipitate for three weeks he claims to have removed all the 

 chromic acid, and says that nothing but chromic oxide remained. By 

 mixing sesquichloride of iron with chromate of potash he prepared a 

 similar chromate of iron, from which all the chromic acid could be 

 removed by washing in the same way. He believed that the calcina- 

 tion of the nitrate of chromic oxide produced a chromate of chromium, 

 but containing always nitric acid, because a heat sufficient to drive 

 oif all the nitric acid also converted the chromate of chromium into 

 chromic oxide. Maus did not analyze quantitatively any of these 

 precipitates, probably because he was embarrassed by the impurities 

 from which he could not free the precipitates without altering their 

 composition ; but his qualitative results are amply sufficient to prove 

 that they all contained cliromic acid as part of their original constitu- 

 tion. Maus did analyze two substances prepared by digesting chromic 

 oxide and ferric oxide in chromic acid ; the results of these analyses 

 were, — 



1. 2. 



CrjOs = 27.79 per cent. FcaOs = 25.06 per cent. 



CrOs = 72.21 " CrOs = 74.94 " 



And he assigned to them the formulae CrgOs 2 CrOs and FcaOs 2 CrOs 

 respectively. These formulae are incorrect ; the figures of the first 

 analysis would give about four equivalents of acid to one of the oxide, 

 and those of the second analysis would give more than four equivalents 

 of chromic acid to one of ferric oxide. Both substances were unques- 

 tionably indeterminate mixtures. Dumas, recounting the experiments 

 of Maus, says, " These results would be decisive, but they are contested 

 by Berzelius." * It is therefore necessary to review the opinions of 

 Berzelius on this subject. 



In 1814 Berzelius, writing an essay on the "Cause of Chemical Pro- 

 portions," t mentions the new oxide of chromium, prepared by Vauque- 

 lin, intermediate between the green oxide and chromic acid. Berzelius 



* Traite de Chimie Appliq., (Liege, 1848,) VII. 319. 



t Thomson's Ann. Phil., III. 104, (1814,) and Schweigger's Jour, fiir Ch. u. 

 Phys., XXn. 56. 



