‘\o the late Mr. Henry. 223 
stances, »which, though themselves destitute 
of; colour,, are important agents in the pro- 
cesses. of Dyeing, Substances of. this kind 
had received, fromthe French dyers, the. name 
of Mordants, because. it was.imagined. that 
they corroded and removed something, which 
mechanically opposed the entrance, of .the 
colouring 1 matter into the. pores of the mate- 
rial to, be dyed. To destroy this erroneous 
assqciation; Mr... Henry. proposes, that, the 
word. basis should; be substituted, as a. general 
term; to, denote, every substance, which yhaving 
an affinity both for the colouring matter, and 
for the. material. to be, dyed, is, capable. of 
serving, as an intermedium between, the two; 
and. that a, spegific, epithet, should be. added, 
to distinguish each particular variety. : In 
this essay, Mr, Henry, for the first time, ex- 
_ plained the true_nature; of, the liquor, which 
isemployed. for affording. the aluminous basis, 
prepared by mixing the solutions of. alum. and 
of sugar of lead. This, liquor. he shewed to 
be ‘essentially a compound of. pure clay or 
alumine with acetic, acid ; 3. and, ts superiority, 
over. -asolution.o of common alum, for yielding 
the earthy base in dyeing, he. ascribes partly 
to the less affinity of the acelic acid, than of 
the sulphuric, for. alumine, and partly to the 
greater volatility . of the acetic acid, when 
