62 Odbfervations on the Art of 
ftuffs may be removed by the fulphurous acid, and fill better 
by the oxygenated muriatic acid, But when the {pots are of 
a complex kind, it will be neceffary to employ feveral means 
in fucceffion. Thus: to deftroy the ftain of coom from car- 
riage-wheels, after the greafe has been diffolved the oxyd of 
iron may be removed by the oxalic: acid. R 
As colours are, often changed by re- agents, it will be ne- 
ecflary, in order to reftore them, that “the fcowerer fhould 
poflefs a thorough knowledge of the art of dyeing, and 
how to modify the means according to circumftances. This 
becomes the more difficult when it is neceflary to re-produce 
a colour fimilar to that of the reft of the fluff, to apply that 
colour only in one place, and often to refiore the mordant by 
Ce 
which it was fixed, and which has been deftroyed, or even. 
the firft tint which gave the colour its intenfity. It may be 
readily conceived that the means to be employed muft depend 
on the nature of the colour and the ingredients by which it 
was produced ; for it is known that the fame colour may be 
obtained from very different bodies. Thus, after an alkali has 
been employed to deftroy an acid fpot on browns, violets, 
blues, poppies, &c. the yellow fpot which remains may be 
made to difappear by a folution of tin ; afolution of fulphat 
of iron reftores the colour to brown ftuffs which have been -— 
ealled'; acids reftore to their former fplendour yellows which 
have been rendered dufky or brown by alkalies; blacks pro- 
duced by logwood become red by acids; alkalies change 
thefe red fpots to yellow, and a little of the aftringent prin- 
ciple makes them again become black. A folution of one ~ 
part of indigo in four parts of fulphuric acid, diluted with a 
fufficient quantity of water, may be employed with fuccefs to 
revive the blue colour of cotton or wool which has been 
changed. Scarlet may be revived by means of cochineal 
and a folution of the muriat of tin, &e. 
The choice of re-agents is not a matter of indifference. 
Vegetable acids are preferable; the fulphurous acid however 
may be employed for ftains occafioned by fruit: it does not 
change the blue of filk nor colours produced by aftringents : 
it does not degrade the yellow of cotton. A:nmonia fuceeeds 
better than fixed alkahes in removing fpots produced by a 
, 
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