pitation. the moft violent in Solution tion upon metallic fubftances, when unaffifted by heat. and Preci- So great indeed is the violence with which this acid fometimes acts, that the metal, iuftead of being difol181 ved, separates inftantaneoufly from it in the form of a Ni-rousacid calx or powder fcarce foluble in any menftruum, at the fame time that the heat, effervefcence, and noxious vapours issuing from the mixture, render it abfolutely neceflary to moderate the action of the menftruum, either by dilution or cold, or both. In other cafes, Lowever, as when put to gold or platina, the nitrous acid has no effect until it be united with the marine, when the mixture acts upon thofe metals, which neither of the acids fingly would touch. its operation. 182 Vitriolic acid acts more weak ly. 183 Marine acid general 3. The action of the vitriolic acid, though in the highest degree of concentration, is more weak. It does not readily attack filver or mercury unless affifted by a boiling heat, nor will even that be fufficient to make it act upon gold or platina. 4. The action of marine acid, unless on fome particular ly more fubitances, is ftill more weak; but when dephlogifticaweak than ted, or deprived of part of the phlogifton effential to cept when its conftitution as an acid, it acts much more powerderhlogifti- fully, and diffolves all the metals completely. either, ex cated. 184 The rest of the acids much weaker ftill. 5. The other acids, as thofe of fluor, borax, with fuch as are obtained from the animal and vegetable kingdoms, are much inferior in their powers as folvents, unless in very few inftances. 6. Metals vary very much in their degrees of folu185 bility; fome yielding to almost every menftruum, and degrees of others, as has been already obferved, being scarce acfolubility in ted upon by the moft powerful. Different metals. Solution f metimes portion of 187 6. Zinc and iron are of the former kind, and gold 186 and filver of the latter, eluding the marine; and gold, unless in one particular cafe, viz. when affifted by heat promoted in a clofe veffel, the action of the nitrous acid alio. by abftract- Thefe metals, however, which in their perfect ftate reing a cerfit the action of the most powerful menftrua, may be tain prodiffolved much more readily when deprived of a cerhlogilon. tain quantity of their inflammable principle. But though the feparation of this principle in fome degree renders metals more foluble, the abstraction of too much But is total- of it, particularly in the cafe of iron and tin, renders ly prevent thefe metals almost entirely infoluble. Manganefe is the ed by tamoft remarkable inftance of this power of the phloking away too much giftic principle, in depriving metals of their folubility exemplified by its ablence, or reftoring it to them by its prefence; in manga for this fubftance, when reduced to blacknefs, cannot be diffolved by any acid without the addition of fome inflammable matter; but when by the addition of phlogifton it has become white, may be diffolved in any acid. uefe. 188 Solution of 7. The diffolution of metals by acids, even to their nietals at very lall particle, is attended by a vifible effervefcence: tended with this is more perceptible according to the quicknefs of an effervef the folution; but more obfcure, and fecarcely to be feen cence. at all, when the felution proceeds flowly. 189 8. The elastic fluids extricated by thefe folutions kinds of e- are various, according to the nature of the acid and of lastic fluids the metal employed. With the nitrous, the fluid proextricated. duced is cominonly that called nitrous air; with vitrio. lic and marine acids the produce is fometimes infammable air, fometimes otherwife, according to the nature of the metal acted upon. Various Heat pro gree of it is in proportion to the quantity of the mat- Solution ter and the quicknefs of the folution; and hence, in and Preci fmall quantities of metal, and when the folution pitation. proceeds very flowly, the temperature of the mass is scarce- 190 ly altered. 10. The calces of metals either yield no air at all, duced duor only the aerial acid, unless when urged by a violent ring the dif heat almoft to ignition; when, by means of vitriolic or nitrous acid, they yield a quantity of pure air, after other elaftic fluids, fuch as vitriolic, nitrous, or phlo- Little air gitticated air. None of the dephlogifticated air is can be ob ufually produced by the marine acid in conjunction metals when calci Various co lours of 11. The folutions of fome metals are coloured, o• ned. thers are not. The colour of the former is only that 192 which is proper to the calx, but rendered more vivid by the moisture. Thus folutions of gold and platina metalic are yellow; thofe of copper, blue or green; folutions calces. of nickel of a bright green; but thofe of cobalt are red, although the calx is black. We may obferve that even this red colour may be heightened to blackness. Iron moderately calcined is green; but this rarely continues upon further dephlogiftication. The white calces of filver, lead, tin, bifmuth, arfenic, antimony, and manganese, are diffolved without colour; but folutions of lead, tin, and antimony, are somewhat yellow, unlefs fufficiently diluted. Mercury, however, forms a fingular exception to this rule; for the orangecoloured cals of this metal forms a colourless folution. The metals yielding coloured folutions are gold, platina, copper, iron, tin, nickel, and cobalt; the rest, if properly depurated, give no tinge. A folution of filver is fometimes of a blue or green colour at firit, although there be no copper prefent; the vitriolic acid becomes blue with copper; the nitrous may be made either blue or green at pleafure; the marine varies according to the quantity of water with which it is diluted. Manganefe, when too much dephlogifticated, renders both the vitriolic and marine acids purple. 193 Bergman's 194 too great a logit in. quantity of 195 With regard to the cause of chemical folutions, our author obferves, that though attraction must be look account f the caufe d ed upon as the fundamental caufe, yet we may alfo hemical lay it down as a maxim, that no metal can be taken folution. up by an acid, and at the fame time preferve the whole quantity of philogiiton which was neceffary to it in its metallic ftate. A certain proportionof the principle of Solution inflammability therefore may be confidered as an ob- impeded by tacle which must be removed before a folution can take place. Thus, of all the acids, the nitrous attracts phlogitton the molt powerfully, and feparates it even from the vitriolic. A proof of this may be had by Sulphur de boiling fulphur flowly in concentrated nitrous acid. phi gutica ted by niAt length all its phlogifton may be feparated, and the trous vitriolic acid will remain, deprived of its principle of inflammability. The extraordinary folvent powers of this acid, therefore, is conformed to the peculiarity of its nature in this respect. For this menttruum diffolves metals for folution with the greatest ease, most commonly without any affiftance from external heat; which 196 in fome inftances would be hurtful, by feparating too fome metals much of phlogifton, as appears in the cafe of iron, tin, prepared by and antimony; all of which may be fo far dephlogifti- bitrous a eated by the nitrous acid, as to be rendered extremely caref difficult of folution: for this reafon it is very often neceffary, as has already been obferved, to temper the wards. activity acid. Calces of infoluble c ver after |