OXIDATION, 3G7 



comes of a beautiful purple hue, in which all kinds of goods capable of being 

 may be dyed {Jthh may be changed to the (int of peach or lilac bjoomVpeaches 

 bloiroms, by increafing the proporiions of the nifro muriatic or lilac j 

 folution; or, on" the other hand, by caufing ihe muriatic fo- or even to grey, 

 lutions of tin to preponderate ; fliades of grey wij! be obtained, the^quantity"o"/ 

 deeper or paler in colour, according to the quantity of the the twoiblutians 

 folution added. Caremuft, however, betaken, in the latter* 

 experiment, that too great a proportion of the muriatic liquor 

 of tin be not ufed ; for by depriving the oxide of gold of too 

 much of its oxigen, it might be loo much difoxided and pre- 

 cipitated. The precipitate caufed by fuch an accident is not The precipltaa 

 li ■ -1 r ■ L- I . •* -ir ,, of the oxide of 



altogether void of oxigen, which prevents its gilding cold „o)j ^yjj, j^^^ 

 fiiver, as do the adies of burned cloth impregnated with the si:dfilver,with- 

 Iblution of gold. The degree to which the prefervation ^^Inleofhe^u' 

 the tin6ture of gold may be carried, muft depend on the pro- 

 portions of the two folutions of tin, their being more or lefs 

 furcharged with acids, and the quality of the folution of gold, 

 wherein alio there (liould be a very great excels of acid. 



The purple tindure of gold, though of tlie mofi perfeft ,^/[?;'^'!°sf "^ 

 tranfparency, is decompofed by expofure to a ftrong heat, and 

 throws down what is known by the name of " Purple of Coffins," 

 vvhofe beauty depends on the quantity of niiro-raurtatic folu~ 

 tion of tin made ufe of. The latter, however, if mixed 

 alone with the folution of gold, without the prefence of mu- 

 riate of tin, produces no alteration of colour, and, if the 

 mixture be not too ratich weakened with water, is a very long 

 lime before it gives a precipitate. 



The purple tincture of gold, is, properly fpeaking, nothing 

 more than the powder of catlius, held in foiution by means of 

 the oxigen of the nitro-muriaiic liquor of tin; and there is 

 every reafon to believe, that in the powder of caffius, the 

 oxide of gold is in fome way coniliined with the oxide of tin, 

 which, by tranfmitting to it its own origin, during its fixation 

 upon porcelain, prevents it, I think, from returning to its 

 metallic Hate. I find a difficulty in (ubfcribing to the opinion 

 of Dr. Richter, of Berlin, who, in a memoir (which I have Di. Rkhtci's 

 not read) attempts to prove, by matht^matical demon Rralion, T^'""^"^^^^^^^^^ 

 that tlie crimfon-coloured gold on porcelain is in the metallic ed gold upon 

 ftale. P°^'''^"; 



The purple tinflure of gold might be advantageoufly ^m- ^^"P]^ ^^^'^^'^^JjJ^ 

 ployed in dying fjlks, without greatly enhancing the price, ^n others for 



The (^ying <»iks« 



