lj6 On the Art of Dying by coloured Oxydes of Tin. 



He then proceeds to give an account of his experiments, conc«rnIng the means of com- 

 bining the colouring matter of madder, cochineal, and all the feveral dying drugs, with tin, in 

 order to fix them immediately on piece-goods, in the way of folution and precipitation. 



His experiments were made on the folutions of tin, by the nitro-muriatic, muriatic, ful- 

 phuric, and acetous acids, and by potafh ; and he mixed the colouring decoiSlions of plants, in 

 feme inftances, with the acid folutions ; in others, with the oxydes precipitated from them ; 

 or, otherwife, he re-diflblved in alkali the oxydes already coloured. The following is a 

 fummary of the principal circumftances and effeiSs of thefe operations. 



When the fluids do not immediately afFord a precipitate, he caufes it to take place by im- 

 merfing a piece of filk, cotton, or woollen. The precipitation, in fome inftances, takes place 

 Jby the fimple mixture of the two liquids, and the refult confifts of oxydes, coloured accord- 

 ing to the nature of the vegetable fubftance. Thefe coloured oxydes appear likely to be 

 ufeful in painting. In other experiments he forms thefe coloured powders, by firft precipitating 

 the oxyde of tin from its acid folution, by the mere addition of water; and the edulcorated 

 oxyde feizes part of the colouring matter from the tindture in which it is plunged. Laftly, 

 thefe coloured oxydes being diflblved by potafh, and the ftufFs impregnated with the folution, 

 the colouring matter afterwards become fixed, either by fimple expofure to the air or by 

 immerfion in an acid folution of tin or of alumine, according to the obje£l propofed by the 

 operator. 



The colours which are produced differ in kind. In fliade, in brightnefs, and in folidity, 

 from various caufes, namely, the fpecies of vegetable, the kind of acid, and the oxydation of 

 the tin ; the portion of acid, or alkali, which may exift in the precipitate, according to the 

 choice ©f the operator; the greater or lefs proportion of water in the folutions ; the other cir- 

 cumftances of manipulation ; or the feveral ingredients which may have been employed. 



Each acid differs principally by the degree of oxydation to which it is difpofed to carry the 

 tin. The nitro-muriatic acid being capable of variation in its dofe of oxygen, is, on this ac 

 count, more or lefs proper to advance the oxydation of the metal. The oxydation is alfo more 

 perfeft, if the folvent be more concentrated, or if the acSlion of heat be added, or if the folution 

 be expedited, by adding a confiderable quantity of the metal at one time. The oppofite con- 

 ditions are attended with the contrary effect. In order to regulate, at pleafure, the greater or 

 lefs oxydation of the metal, and in fome meafure at the will of the operator, it will be fufficient, 

 if, to a nitro-muriatic folution of tin, there be added a certain quantity of the muriatic folu- 

 tion of the fame metal ; for this laft may eafily be obtained at the leaft poflible degree of ox- 

 ydation. 



It is a well-known fail, that the fpontaneous progrefs of the oxydation of the folutions of 

 tin, or the addition of water, in fufficient quantity, caufe the fepuration of a precipitate. This 

 effe6l maybe prevented when neceffary, by leaving or adding an excefs of acid to the folution; 

 or by adding a quantity of the muriatic folution of tin, which has the property of fupporting a 

 much greater quantity of water without precipitation ; or, laftly, by adding muriate of foda, 



or 



