J. M. Ordway on Sesquisalts. 201 
ing, a protacetate of iron made with crude pyroligenous acid, is 
found to answer a better purpose than a purer acetate. Some 
chemists account for this by saying that the pyrogenous matters ae 
_ prevent the oxydation of the iron from going too far in the dry- “eae 
ing and aging of the cloth. But granting it to be the magnetic a 
oxyd which goes to make a black dye, it must be admitted that 
_ the vegetable principles of the tannin family themselves readily * 
reduce an active peroxyd of iron to the right degree of oxydation ; ey 
or careful experimenters have proved that the full persalts can 
be made to give good blacks and purples. The good effects of 
pyroligneous acid must be owing mainly to its power of presery- § 
ing the oxyd of iron in the active state. The normal ferric salts ri 
are too acid and corrosive to be safely used on cotton; but some- , 
thing might be gained by employing the tribasic pernitrate which : 
1s not liable to passivity, and would probably do away or at 
least shorten the “ aging” process—there being no acetic acid to 
get rid of by long exposure. Pees 
The polybasic nitrates of iron formed by direct combination, 
have been already examined, and it was shown that at least 
eight equivalents of the oxyd might be held in solution by one. 
equivalent of acid. We cannot go quite so far by the method 
tion of a rust 
must be free from a “chlorid of the precipi 
Since the hydrate was made from the erystallized nitrate, 
