'Ofi tie Art cf Dying by coloured Oxydes of Tin. I77 



or any other muriatic fait the eW^fi of which feems to be, that they faturate the excefs of 

 water which would elfe have occahor.jd pi^cipitation. 



To haftea the muriatic folution of our metal, it is advantageous to fprinkle it with the con- 

 centrated acid, and then leave it expofed to the air. The furface of the metal becomes oxyded 

 with fuch rapidity, that a fenfible heat may be produced ; arifing, no doubts from the caloric 

 taicen from the oxygen gas abforbed from the atmofphere. 



The muriatic folution of tin, when concentrated, affords many cryftals at the temperature 

 of ice, and thefe cryftals are peranaiient in a cold place. The heat of thirty or forty degrees 

 above zero (q. of Reaumur?) liquifies them. When difTolved in water, they afford a folution 

 of tin, which may be ufed as occafion requires. This folution becomes oxyded to the maximum 

 (and will, confequently, produce difFerent efFefls on the colouring fubftances) if it be left 

 expofed for a certain time to the air, the contadl being favoured by an extenfive furface. 



The oxyde of tin, precipitated from its muriatic, or nitro-muriatic folution, by an alkaline 

 carbonate, may, if not too much oxyded, be very eafily, and without decompofition, diflblved 

 in the diluted nitric or fulphuric acids, and alfo in the acetous acid. Thefe folutions produce, 

 "with colouring fubftances, fhades, which are more efpecially governed by the oxydation of the 

 tin, and are difpofed to change more or lefs fpeedily in the air, by a fuperoxydation of the 

 metal, and according to the nature of the folvent. The fulphuric acid accelerates this effeA 

 more than the nitric, and the acetous acid the moft rapidly of any ; which circumftance fliews 

 that the acetic folution of tin, if it be required to be kept without fpontaneous precipitation, 

 muft be preferved in well-clofed bottles ; and that, on this account, it would be preferable to 

 the muriatic folution for eudiometric cfTays. 



The difpofition of the coloured oxydes of tin to change their fhade by fuperoxygenation from 

 the air, appears to depend on the circumftance that they retain a portion of the acid folvent. 

 If, on the contrary, they fliould retain a portion of alkali, the fhade is difFerent, and continues 

 fixed in its firft ftate. Thefe precipitates do not, however, appear to unite with the carbonic 

 acid, whether it be that this acid has very little attraction for the oxyde of tin, or whether, as 

 is more probable, that the colouring fubftances exclude it. 



A very remarkable phenomenon takes place in thefe changes of fhade, by the degree of ox- 

 ydation, when the infufion of cochineal is made ufe of: the leaft-oxyded precipitates are of a 

 violet colour, which by expofure to the air becomes more or lefs fpeedily converted into beauti- 

 ful carmines. Ammoniac caufc-s them to approach fomewhat towards crimfon ; but they pre- 

 ferve their primitive colour, and are even more beautiful when the ammoniac has evaporated. 

 If this alkali were employed upon the carmine red produced by precipitation from the nitro - 

 muriatic acid, the new fhade would be brown, and would not recover its original luftre. 



In general this kind of colours depends on feveral complicated circumftances : when applied 

 on piece-goods, they refilt the adion of acids better than that of the air and the fun. They 

 become ftill more unchangeable by fiibftituting, inftead of the nitro.;muriatic folution of tin, that 

 made with muriatic acid, or a ir/iHtire of both. The coloured oxydes appear likewife to gain 

 both in folldity and brilliancy when they are prepared by a folution of which the acid is not ca- 

 pable 



