oxide of iron that are capable of forming peculiar acids with the ele-
ments of prussic acid :' and the most remarkable of these is sulphur,
which makes an acid of a red colour, having always the same pro-
perties, though fonned in various difi'erent ways. The first method
by which Mr. Porrett formed this acid, was by boiling together sul-
phuret of potash with prussiau blue: but he has also made it by the
same sulphuret with prussiate of mercury. Also by heating together
sulphuret of potash with animal charcoal, and by sulphate of potash
with the same coal. Also by boiling a simple alkaline prussiate with
sulphur, or by mixing prussiate of ammonia with hydroguretted sul-
phuret of potash. Since one of the properties of this acid is to form
an insoluble compound with copper, the author takes advantage of
this valuable property for obtaining the acid in a pure state. After
decomposing asalt of copper for this purpose, a quantity of sulphuric
acid is poured on the precipitate, and the whole submitted to gentle
distillation, by which the acid is obtained nearly pure, or may be
easily purified. -The author examines the salts formed by union of
this acid with the several alkalies, earths, and metallic. oxides, show-
ing that it may be transferred from one to another without change of
its properties, and supporting his opinion that it should be regarded
as an acid of a peculiar and extremely compound nature.
For the acids here described, the author invents names by com- bining the initials of three of their constituents, carbon, hydrogen, and azote, which give him the term Chyazic; and hence he deno- minates the former Fermretted Chyazic acid, and the latter Sulphu- retted Chyazic acid. By careful analysis of the former, the author found 17'26 oxide of iron in 47-66 of the dry acid: and in 18'4 of the latter he found 12 of sulphur.
In the course of these experiments Mr. Porrett examines and de- scribes. the precautions which are necessary in ascertaining the quan- tity of iron present in any solution by the quantity of prussian blue that can he formed: and he also shows the use that may be made of the sulphuretted chyazates as precipitants of copper. He observes. that the precipitate formed in this case contains no water, and con- sists of about 63 protoxide of copper, combined with 37 sulphuretted chyazic acid.
Notwithstanding the many accurate experiments which have been made and recorded, showing that diamond and carbonaceous substances combine with the same quantity of oxygen, and form the same quantity of carbonic acid, various conjectures have been formed respecting some difference in their chemical composition, which might account for the remarkable difference in various sensible qualities. Messrs. Biot and Arngo conjectured, from the great refractive power of the diamond, that hydrogen must he present. Guyton de Morveau
