[ 482 ]

In the foregoing experiments, the precipitates of pla-tina by volatile alcalies were of a dark kind of red colourand considerably sparkling, while those by the fixt were ofa paler dull reddish with little brilliancy. In the ac-counts which others have given of these precipitations,this difference, in itself of small importance, is not takennotice of. Scheffer calls the precipitates by both alcaliessimply red; and Marggraf calls them both orange yellow,a term applicable enough to the precipitates which I hadobtained with the fixt alcalies, but not to those with thevolatile. It should seem as if there had been some realdifferences in the appearances of our respective products,and I imagined that such differences might have arisenfrom differences in the solutions of platina made useof: some late trials appeared to countenance this suspicion,for while common solutions of platina yielded precipitatesof the red kind, a solution of the crystals of platina madein water gave only yellow ones.

Macquer accounts for this difference of colour in anothermanner. He fays the precipitate proves red only when thequantity of alcali is no more than just sufficient to satiatethe acid ; and that the more of the alcaline liquor we addbeyond this point, the precipitate proves less and less red;agreeably to which his coadjutor Baume fays afterwardsmore determinately, in his mannel de cbymie, that with adue quantity of fixt alcali the precipitate is orange yellow,and with an over quantity pale yellow. Mr. Macquer,judging from hence, that the redness was owing to a largequantity of acid retained by the platina, digested some ofthe red precipitate in a solution of fixt alcaline fait: thealcaline liquor, absorbing the acid, destroyed the red co-lour of the powder, and made it white. It has long beenknown, that precipitates carry down with them a portionboth of the dissolvent and of the body they were precipi-tated