‘ of Atmospherical Arr, Sc. 149 
that acid; in which case, the superfluous oxygen 
combines with and oxygenates the muriatic acid. 
« Iron,” continues our author, “ which has real- 
ly imbibed air, or the common rust of iron, has a 
very different appearance from finery cinder, being 
-yed and not black.”—-Aware that the answer to this . 
is, that these two substances are oxydated in different 
degrees, he adds, “that if finery cinder were iron 
partially oxygenated, it would go on to attract more 
oxygen, and in time become a proper rust of iron.” 
—And so it really does. Iron filings exposed to 
a long continued heat with access of air, under 
the muffle of an assaying furnace, become first an 
oxyd of a blackish colour, and afterwards the red 
oxyd, which was formerly called crocus martis ad- 
stringens, which has the same properties as rust of 
iron. In this process, the iron is first converted - 
into finery cinder (as is uniformly the case, when it 
is heated in the presence of atmospherical air) which 
is afterwards converted into rust, by a continuance 
of oxydation. Moreover the black oxyd of iron 
(which is obtained by the method discovered by Le- 
mery, viz. by keeping iron-filings under water for 
some time; during which process the iron acquires 
weight, and hydrogen gas is produced, according to 
the observations of Lavoisier and Rinmann) will . 
become the red oxyd of iron, not only by heat- 
ing it with access of air, but also in the habitual 
