228 On the Precipitation of the Oxide of Gold hj Potash. 



asserted that the alkalis did not precipitate tiie solution of gol'i 

 in the ci'Id way. M. Oberkampf had obtained a contrary result; 

 but he thought he could account for this difference bv the ex- 

 cess of acid of the solution, which gave rise, witli the precipitat- 

 iiiy; alkali, to the formation of a great quantity of triple salt, in- 

 decomposable, at least totally, by an excess of base ; for it is 

 certain tliat there is no ))recipitate made in the cold way in the 

 space of several minutes, even with ammonia, when the excess 

 of acid is suificient. The object of M. Figuier is to prove that 

 the excess of acid of the solution of gold does not prevent the 

 precipitation of the oxide by an alkali, and that we obtain nearly 

 as much of it as from a solution as neutral as possible. 



" Six grammes of dry muriate of gold," says M. Figuier, 

 "^ v/ere dissolved in 150 grammes of distilled v,-atcr ; the solu- 

 tion when filtered v.as divided into two equal parts, and put 

 into two conical glasses. Into one I poured four grammes of 

 nnn-iatic acid: I saturated both solutions with caustic potash 

 dissolved in water : their yellow colour became a deep red. A 

 ihort time afterwards, the liquors became turbid : a flaky 

 jnccipitate of a gray colour was developed : these precipitates 

 iiicreased after some time and became deeper: — after fortv- 

 cight hours they appeared to be at their maximum of augmen- 

 tation and colour. I observed no dilfercnce between the two, 

 only that in order to produce it, we must employ a greater por- 

 tion of potash in the acid muriate of gold, than in that which is 

 less so ; but I constantly observed that in both cases it was re- 

 quisite that the potash should be in excess, in order to make the 

 precipitates abundant. After having filtered these liquors se- 

 parately, I put them into small retorts and exposed them to the 

 action of a moderate heat; new precipitates were still formed 

 much deeper in colour. I added them to the first, washed them 

 with puie water, and dried them. When weighed in this state 

 their weight represented two-thirds of the gold which was in 

 solution ; — that obtained from the acid solution did not differ 

 from that which had only a decigramme of acid. The liquors 

 which had furnished these precipitates still contained gold: thev 

 became yellow by the affusion of the* muriatic acid, and gave new 

 precipitates by potash, although there was an excess of acid be- 

 fore the addition of the alkali, so that by treating them alter- 

 nately by potash and muriatic acid, I succeeded in extracting 

 the whole gold contained in the muriate, as I have stated iu 

 a former paper. 



Nule by M. Gay-Lussac. — If we can separate the whole 

 gold of the solution by means of the alkalis, it is undeniable that 

 the triple salts are entirely decomposed by an excess of base : 

 nevertheless, if the observation of M. Figuier be exact, that in 



order 



