in dyeing Colton. 5S 
Yiquors. It is both a curious and eafy experiment, that 
when cotton is made to pafs through a folution of the ful- 
phat of iron, rendered turbid by the-oxyd which remains 
fufpended in the liquor, it will be fufficient to dip the 
cotton in the bath to catch the laft particle of the oxyd, 
and to reftore to the liquor the tranfparency it has loft. 
The folution then, which before had a yellowifh appear- 
ance, becomes more or !efs green, according as it is more 
or lefs charged. 
The colour given to cotton by the oxyd of iron becomes 
darker, merely by expofure to the air; and this colour, foft 
and agreeable when taken from the bath, becomes harfh 
and ochry by the progreffive oxydation of the metal. The 
colour of the oxyd of iron is very faft: it refifts not only 
the air and water, but alfo alcaline leys, and foap gives it 
fplendour without fenfibly diminithing its intenfity. It is on 
account of thefe properties that the oxyd of iron has been 
introduced into the art of dyeing, and been made a colour- 
ing principle of the utmoft value. But I have been able to 
give a new extenfion to the applications of this oxyd; and I 
fhall here confine myfelf to the only refults I have obtained 
worthy of entering into the operations of the dye-houfe, 
and which have been employed with fuccefs for feveral years 
in my manufactory. 
In order that the oxyd of iron may be conveniently ap- 
plied to the cotton thread, it is neceffary to begin by effect- 
ing its folution, and in this cafe acids are employed as the 
moft ufeful folyents. Dyers almoft every where make'a myf- 
tery of the acid which they employ; but it is always the 
acetous, the fulphuric, the nitric, or the muriatic: Some 
of them afcribe great differences to the folution of iron by 
the one or the other acid, but in general they give the pre- 
ference to the acetous. This predilection appears’ to me to 
be founded much lefs: on the difference of the colours that 
may be communicated by the one or the other falt, than on 
‘the different degrees of corrofive power which each exercifes 
E4 on 
