the Attractive Powers of Mineral Ac 'As. 83 
fey reafon of the dephlogiftication, or of the union of the 
calces to each other. 
Iron does not precipitate this regulus intirely from the marine 
acid, but a triple fait fee ms to be formed, confiding of the 
acid and both calces. The regulus is alio foluble in marine fait 
of iron. 
Neither does copper precipitate the regulus from marine acid 
in 16 hours; and if the regulus be put into marine fait of 
copper it w ill be diflolved, and volatile alkalies will not give 
a blue but a yeiiowiih white precipitate, fo that here alfo a 
triple fait is formed. 
Of Precipitations of and by regulus of arfenic. 
The dilutions of arfenic act in mod cafes like two acids : 
thus iron, copper, lead, nickel, and zinc, are acted on by- 
vitriol of arfenic (that is, its dilution in vitriolic acid) but 
fcarce give any precipitate. 
Neither does iron precipitate arfenic from the nitrous acid, 
but copper does, and even diver gives a flight white precipitate ; 
but regulus of arfenic precipitates diver completely in 16 hours. 
Hence the former precipitate leems to be a triple fait. 
Mercury alfo {lightly precipitates arfenic from the nitrous 
acid, and feems to unite to it, yet is itfelf precipitated by 
regulus of arfenic in 24 hours. 
Wifmuth forms a flight precipitate in the nitrous dilution of 
arfenic ; but regulus of arfenic forms a copious precipitate in the 
nitrous dilution of wifmuth ; fo that I believe the calces unite. 
Nickel does not precipitate arfenic from the nitrous acid, but 
both calces unite ; but regulus of arfenic produces a copious pre- 
cipitate in the nitrous dilution of nickel, yet the liquor continues 
M 2 green ; 
