OF ARTS AND SCIENCES. 225 



While it is much easier to obtain the manganate of manganese in a 

 state of tolerable purity than it is to prepare the chromate of chromium, 

 because of the greater insolubility of the first substance, it would never- 

 theless be very difficult, to say the least, to precipitate it by the method 

 of double decomposition. We can readily mix chromate of potash and 

 a normal salt of chromic oxide, and throw down the chromate of chromic 

 oxide : till we can prepare a pure and neutral manganate of potash, the 

 true composition of the manganate of manganic oxide cannot be illus- 

 trated in this w^ay. 



IV. Other Chromates of Chromic Oxide. 



Under the head of " Bichromate of Chromic Oxide " the English 

 Editor of Gmelin's Handbook of Chemistry * has described two pro- 

 cesses, neither of which has any connection with the name and for- 

 mula at the head of the paragraph ; the first is the description of a 

 washed, and therefore basic, chromate of chromic oxide, prepared by 

 Traube,t identical with the substance analyzed by Rammelsberg, as 

 Traube himself remarks, and having the same formula by Traube's 

 analysis, viz. (Crj 03)3 (Cr03)2; the second is the description of the 

 mode of precipitating the chromate of chromic oxide, Cr203 CrOs, from 

 chrome alum by chromate of potash in the manner we have fully ex- 

 plained. 



For the existence of what the translator of Gmelin's | Handbook 

 calls the " Neutral Chromate of Chromic Oxide," with the formula 

 CrgOa 3 CrOs, there seems to be no sufficient evidence. Unverdorben, 

 Berzelius, and Maus have proved beyond a question, what hardly re- 

 quired proof, that when heated above the melting point chromic acid is 

 ultimately resolved into oxygen and chromic oxide. Traube § has 

 thought to show that by using a temperature but little above 250° a 

 definite chromate can be obtained, corresponding to the formula 

 CraOg 3 Cr03. By heating a quantity of chromic acid to this re- 

 is described, preparatory to the roasting of the manganous salt or oxide. The more 

 manganic acid formed by the roasting the better, — may not then the admixture of 

 a certain amount of these bases be chemically advantageous ? Very possibly there 

 are mechanical advantages to be gained by their removal. 



* Handbook of Chemistry, IV. 11.5 (Cavendish Soc. Ed.). 



t Ann. der Ch. u. Pharm., LXVI. 108 (1848). 



t Handbook of Chemistry, IV. 116 (Cavendish Soc. Ed.). 



§ Ann. derCh. u. Pharm, LXVI. 106 (1848). 

 VOL. V. 29 



