touching his Theory of Light and Colours. 219 



bodies whatever seem to depend on nothing but the various 

 sizes and densities of the particles, as I think you have seen 

 described by me more at large in another paper. If the par- 

 ticles be very small (as are those of salts, vitriols, and gums), 

 they are transparent; and as they are supposed bigger and 

 bigger, they put on these colours in order, black, white, yel- 

 low, red; violet, blue, pale green, yellow, orange, red; pur- 

 ple, blue, green, yellow, orange, red, &c, as it is discerned by 

 the colours, which appear at the several thicknesses of very 

 thin plates of transparent bodies. Whence, to know the causes 

 of the changes of colours, which are often made by the mix- 

 tures of several liquors, it is to be considered how the parti- 

 cles of any tincture may have their size or density altered by 

 the infusion of another liquor. When any metal is put into 

 common water, it cannot enter into its pores, to act on it and 

 dissolve it. Not that water consists of too gross parts for this 

 purpose, but because it is unsociable to metal. For there is 

 a certain secret principle in nature, by which liquors are so- 

 ciable to some things and unsociable toothers; thus water 

 will not mix with oil, but readily with spirit of wine, or with 

 salts; it sinks also into wood, which quicksilver will not; but 

 quicksilver sinks into metals, which, as I said, water will not. 

 So aquafortis dissolves D , not 0; aqua regia ©, not D, 

 &c. But a liquor, which is of itself unsociable to a body, ' 

 may, by the mixture of a convenient mediator, be made soci- 

 able ; so molten lead, which alone will not mix with copper, 

 or with regulus of Mars, by the addition of tin is made to mix 

 with either. And water, by the mediation of saline spirits, 

 will mix with metal. Now then any metal put in water im- 

 pregnated with such spirits, as into aquafortis, aqua regia, 

 spirit of vitriol, or the like, the particles of the spirits, as they, 

 in floating in the water, strike on the metal, will by their so- 

 ciableness enter into its pores and gather round its outside 

 particles, and by advantage of the continual tremor the par- 

 ticles of the metal are in, hitch themselves in by degrees be- 

 tween those particles and the body, and loosen them from it; 

 and the water entering into the pores together with the saline 

 spirits, the particles of the metal will be thereby still more 

 loosed, so as by that motion the solution puts them into, to be 

 easily shaken off, and made to float in the water : Fig. 3. 

 the saline particles still encompassing the metallic 

 ones as a coat or shell does a kernel, after the man- 

 ner expressed in the annexed, in which figure I 

 have made the particles round, though they may 

 be cubical, or of any other shape. 



If into a solution of metal thus made be poured a liquor, 



Q2 



