OF ARTS AND SCIENCES. 27 



On the other hand, Fischer's salt is an almost constant product of 

 the action of the alkaline nitrites upon salts of the decamin series. I 

 have already mentioned its occurrence among the products of the action 

 of potassic and sodic nitrite upon chloride of purpureocobalt. When 

 nitrate of xanthocobalt is boiled with potassic nitrite and a little acetic 

 acid, Fischer's salt is formed in abundance, and the nitrate is gradually 

 decomposed, without formation of any other product which I could 

 detect. 



Chromate. — When neutral potassic chromate is added to a solution 

 of nitrate of xanthocobalt, a beautiful yellow crystalline precipitate is 

 thrown down, which may be washed with cold water, in which it is but 

 slightly soluble. Hot water also dissolves this salt in very small quan- 

 tity. The chromate has the formula 



Co,(NH3),„(NO,),(CrOJ,+ 20H^ 



as the following analyses show : — ■ 



0-4340 gr. gave 0-3652 gr. CrO,Ba= 35-96 per cent CrO^. 

 0-3472 gr. gave 0-2900 gr. CrO^Ba^ 35-70 per cent CrO^. 

 0-6954 gr. gave 0-3370 gr. water = 5-38 per cent hydrogen. 



The salt lost only 0-68 per cent water on drying up to 145° C. 



The formula requires 35-84 per cent CrO^, and 5-24 per cent 

 hydrogen. It is remarkable that the salt should retain its water of 

 crystallization at so high a temperature. The neutral chromate of 

 xanthocobalt furnishes the most convenient method of obtaining the 

 chloride and sulphate of xanthocobalt in a state of purity. For this 

 purpose the chromate is to be boiled with water and a little acetic acid, 

 and a solution of baric chloride added until baric chromate is no longer 

 formed. From the filtrate the chloride of xanthocobalt crystallizes 

 readily, and a second crystallization gives the salt perfectly pure. The 

 sulphate may then be prepared from the chloride by double decomposi- 

 tion with argentic sulphate. In the preparation of the chloride by the 

 above process, it is not necessary to operate with pure nitrate, but the 

 crude salt and solutions obtained directly by the action of the red gases 

 upon cobaltic nitrate and ammonia may be employed. I am even dis- 

 posed to consider double decomposition of the chromate with baric 

 nitrate the easiest method of obtaining a perfectly pure nitrate of 

 xanthocobalt. 



Dichromate. — Potassic dichromate produces in strong solutions of 

 nitrate of xanthocobalt a beautiful orange-yellow precipitate of crys- 

 talline needles, easily purified by recrystallization, a few drops of 



