SS On the lest Met hqd of decomposing 



that the potash has been entirely saturated with chromip 

 acid. 



This decomposition being effected, the mass is to bp 

 well lixiviated, ihe residue is then to be treated, when hot, 

 with muriatic acid diluted in water, which takes up the 

 iron, magnesia, alumine, and silex, divided by the action 

 pf the potash and the subtraction of the cl^romic acid. 



The solution being terminated, the acid liquor is speedily 

 "decanted, otherwise it would go into a jelly, and it would 

 then be very difficult to separate the undecomposed chro- 

 niate : the latter is to be once more treated as at first ; but 

 instead of? employing the same quantity of nitre, a fourth 

 part will be sufficient. When the chromate of iron is twr 

 .^irely discomposed, we mix the solutions of alkaline chro- 

 mate, m order to saturate them by the nitric acid, after 

 .which it is proper to crystallize this chromate, as wrll in 

 .order to separate some portions of earth which would' have 

 .be<.'n dissolved by the excess of acid, as to take up a little 

 phromate of iron, which is separated in brown dust by the 

 progress of evaporation. We redissolve in water, filter, 

 and precipitate the liquor by a solution of nitrate pf mer- 

 cury at i\\Q minimum , containing the least possible quantity 

 of acid in excess. 



Even supposing that the chromate of potash has been 

 purified as we have indicated, i. e. that it contains neither 

 earthy substance nor muriate, the chromate of mercury is 

 precipitated in a more or less intense colour, accordmg to 

 the state of concentration of the solutions, their tempera- 

 ture, and excess of acid. In some circumstances the mole- 

 cules of this salt, by approaching each other more slowly, 

 assume more acfgregation, even crystallize, and thereby 

 acquire a deeper red colour. We niay also remark that 

 the first portions precipitated are the palest, because, in pro- 

 portion as we subtract chromic acid, it has the same efiect 

 on chromate of potash as if we diluted the liquor. To con- 

 clude, the colour has no influence on the quality of the 

 chromate of niercury. 



When the mercurial solution is employed at the mini' 

 mum of oxidation, and as neutral as possible, there re- 

 n)ains nothing in the mother water exce()t nitrate of potash 

 and nitrate of mercury when a superabundance of these 

 has been introduced : but in general these mother waters 

 retain an amethyst colour, aiid yield with the alkalis a pale 

 green precipitate, which, when heated, leaves oxide of 

 chrome. 



I have 



