465 On the Ufe of the Owyds of Iron 
on the fluff. That of the fulphat and muriat is fo great, 
... that, ifthe ftuff be not wafhed when it comes from the bath, 
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it will certainly be burnt; whereas folutions by the acetous 
or any other vegetable acid are not attended with the like 
& "e . 
inconvenience. 
_ + Tronappears to be at the fame degree of oxydation in the 
different acids, fince it produces the fame fhade of colour 
avhen’ precipitated; and any acid folvent may be employed 
indifcriminately, provided the nature of the falt and the 
degree of the faturation of the acid be fufficiently known ; 
for the fubfequent operations may be then directed according 
to this knowledge, and the inconveniences which attend 
the ufe of fome of thefe falts may be prevented. This 
without doubt is a great advantage which the man of fcience 
enjoys over the mere workman, whois incapable of varying 
his procefs according to the nature and ftate of the falts 
which he employs. 
In this paper I ‘fhall confine myfelf to making known 
the colour that may be obtained from the oxyd of iron, rit, 
employed alone on ftuff which has received no previous pre~ 
paration ; 2d, employed together with madder on ftuff pre- 
pared to receive the Adrianople red. 
v. If the fulphat of iron or any other martial falt be 
diffolved in water, and cotton be dipped in the liquid, the 
cotton will affume a chamoy colour, more or lefs dark ac- 
cording as the folution is more ar lefs charged. The affinity 
of the cotton to the iron is fo great, that it attraéts the me- 
tal, and takes it in a great meafure from the acid by which 
it was’ diffolved. 
3. If the iron of a pretty firong folution be precipitated 
by an alcaline liquor that fhews five or fix degrees (by the 
areometer af Baumé), the refult will be a greenith blue 
magma, The cotton macerated in this precipitate aflumes 
at firft an unequal tint of dirty green; but mere expofure ta 
the air makes it in q little time turn yellow, and the fhade is 
very dark, 
js Tj 
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