VOL. LXXIII.] PHILOSOPHICAL TRANSACTIONS. 343 



from its acid and calomel formed, 1 Margraaf 284 ; and yet, if calomel and 

 silver be distilled, the mercury will pass in its metallic form, and horn silver will 

 be formed, ibid. 286. 



Of precipitations of and by bismuth. — With respect to the vitriolic acid I have 

 made the sum of the quiescent and divellent powers equal, though in fact some- 

 times the one preponderates and sometimes the other. Bismuth precipitates 

 nothing from vitriol of copper in 1(5 hours; nor does copper from vitriol of 

 bismuth. Copper is said to precipitate bismuth from the nitrous acid ; but I 

 have also seen copper precipitated from this in its metallic form by bismuth. The 

 variations proceed from the different dephlogistication of copper. 



Of precipitations of and by nickel. — Unless nickel be pulverised it scarcely 

 precipitates any metal. Zinc precipitates a black powder from the solution of 

 nickel in the vitriolic and nitrous acid, which Mr. Bergman has shown to con- 

 sist of arsenic, nickel, and a little of the zinc itself. The arsenic attracting the 

 calx of nickel ; but zinc precipitates nickel from the marine acid. 



The solution of iron in vitriolic acid acts on nickel, and that of nickel in this 

 same acid acts on iron ; but neither precipitates the other in 24 hours ; but on 

 longer rest, iron seems to have the advantage ; but iron clearly precipitates 

 nickel from the nitrous acid ; and though nickel seems also to precipitate iron, 

 yet this arises only from the gradual dephlogistication of the iron. 



Nickel precipitates copper in its metallic form from the vitriolic acid. It also 

 precipitates copper from the nitrous and marine acids ; but copper precipitates 

 arsenic from a nitrous solution of nickel. The vitriolic and nitrous solutions of 

 lead seem to act in specie on nickel, that is, to dissolve it without any decom- 

 position, the calces uniting to each other. The vitriolic and nitrous solutions of 

 nickel for some time act on lead in the same manner ; but at last nickel seems to 

 have the advantage. With regard to the marine acid, lead seems to have the 

 advantage, though a black precipitate is seen, whichever of them is put into the 

 solution of the other. 



Nickel readily precipitates bismuth from the vitriolic and nitrous acids ; but as 

 to the marine I found each of these semi-metals soluble in the solution of the 

 other, yet nickel precipitates bismuth very slowly, and only as to part ; and 

 bismuth precipitates a red powder, which I take to be ochre, from the solution 

 of nickel. 



Nickel and tin are slightly acted on, each by the salt of the other. 



Of precipitations of and by cobalt. — Cobalt is not precipitated either from the 

 vitriolic or nitrous acid by zinc ; but it seemed to be precipitated by zinc from the 

 marine acid. Though iron precipitates cobalt from the three acids, yet I found 

 much of the cobalt retained both by the vitriolic and nitrous acids, particularly 

 the latter, which, after letting fall the cobalt, afterwards re-takes it, and lets fall 



