a» 
re 
On the Process of Bleaching. 299 
arts is less indebted to him than that of changing 
the colours of substances. The art of dyeing has 
attained a high degree of perfection without 
the aid of the chemist, who is totally ignorant 
of the rationale of many of its processes, and the 
little he knows of this subject is of a late date. 
The process of dyeing the turkey-red has been 
known and practised from time immemorial, by the 
most uncultivated nations, but its theory is not yet 
understood by philosophers. ‘The manufacture of 
indigo and its application have been long known to 
the planter and the dyer; but it is not more than 
ten years since a true theory of them has been form- 
ed. The art of printing, or topical dyeing, is of 
the greatest antiquity; but the theory of this pro- 
cess, and of adjective colours in plain dyeing, was 
unknown, till Mr. Henry developed it in the 
Memoirs of this Society.* He was the first who 
thought and wrote philosophically on this sub- 
ject. The bleaching or whitening of vegetable 
substances has been long practised ; but the know- 
ledge of its theory could not be antecedent to the 
gra of pneumatic chemistry, We might, even at 
this moment, have been unacquainted with the cause 
of the destruction of the colouring matter of ve- 
getable substances, if the discovery of the oxyge- 
nated muriatic acid, and its effects on colouring 
matter, had not pointed it out to us. For this dis. 
coyery and its inestimable advantages, the arts aye 
* Manchester Memoirs, vol, iii, 
