3 14 PHILOSOPHICAL TRANSACTIONS. [ANNO 1783. 



the dephlogisticated calx of iron. Nickel also, though it does not precipitate 

 cobalt itself, as appears by the remaining redness of the solution, yet constantly 

 precipitates some other heterogeneous substance from it. The solution of cobalt 

 in the marine acid becomes colourless by the addition of nickel. Bismuth is 

 soluble in the vitriolic and nitrous solutions of cobalt, and causes a small white 

 precipitate, but does not affect the true cobaltic part. These solutions in 

 vitriolic acid cannot be attributed to an excess of acid, as they are made in a 

 dilute acid, and without heat. Copper also precipitates a white substance from 

 the nitrous solution of cobalt, which I take to be arsenic. 



Of precipitations of and by regulus of antimony. — Copper neither precipitates, 

 nor is precipitated from, the vitriolic acid by regulus of antimony, at least in 3 

 days ; but vitriol of antimony in specie dissolves it slowly. The regulus is also 

 acted on by vitriol of lead, for it becomes red after remaining l6 hours in the 

 solution of that vitriol ; and lead scarcely precipitates it from the vitriolic acid. 

 Powdered regulus precipitates vitriol of mercury very slightly. Bismuth neither 

 precipitates, nor is precipitated by this regulus from the vitriolic acid in 24 hours. 

 Though tin precipitates this regulus from the nitrous acid, yet if the regulus be 

 put into a solution of tin in this acid, in l6 hours neither will be found in the 

 solution, either by reason of the dephlogistication, or of the union of the calces 

 to each other. Iron does not precipitate this regulus entirely from the marine 

 acid ; but a triple salt seems to be formed, consisting of the acid and both calces. 

 The regulus is also soluble in marine salt of iron. Neither does copper precipi- 

 tate the regulus from marine acid in id hours ; and if the regulus be put into 

 marine salt of copper it will be dissolved, and volatile alkalis will not give a blue 

 but a yellowish white precipitate, so that here also a triple salt is formed. 



Of precipitations of and by regains of arsenic. — The solutions of arsenic act 

 •in most cases like two acids : thus iron, copper, lead, nickel, and zinc, are acted 

 on by vitriol of arsenic (that is, its solution in vitriolic acid) but scarce give any 

 precipitate. Neither does iron precipitate arsenic from the nitrous acid, but 

 copper does, and even silver gives a slight white precipitate; but regulus of ar- 

 senic precipitates silver completely in 16 hours. Hence the former precipitate 

 seems to be a triple salt. Mercury also slightly precipitates arsenic from the ni- 

 trous acid, and seems to unite to it, yet is itself precipitated by regulus of arse- 

 nic in 24 hours. Bismuth forms a slight precipitate in the nitrous solution of 

 arsenic ; but regulus of arsenic forms a copious precipitate in the nitrous solu- 

 tion of bismuth ; so that I believe the calces unite. Nickel does not precipitate 

 arsenic from the nitrous acid, but both calces unite ; but regulus of arsenic pro- 

 duces a copious precipitate in the nitrous solution of nickel, yet the liquor con- 

 tinues green ; so that certainly the nickel is not precipitated; the white precipi- 

 tate in this case seems to be slightly dephlogisticated arsenic. This regulus also 



