130 Remarks on Priestley’s Analysis 
the attraction, which the substances under operation 
haye to moisture, with which they may combine, or 
which they may decompose, and thereby produce 
-etrors; but also on account of the air which water 
contains, and which may be expelled by the-heat of 
the operation, or attracted by the bodies under ex- 
amination:—It is known that iron in that first de- 
gree of oxidation, formerly called martial ethiops, 
is capable of, combining with so much oxygen, 
as to.increase in weight from 30 to 35 per cent. 
Why. then were there employed 24 ounce-measures 
only of atmospherical air with 200 grains of needles, 
though twenty times as. much is necessary to satu- 
rate the iron and produce a decisive effect ?—Bones 
are not a proper substance for experiments of this 
nature, because they contain ammoniac and conse- — 
quently azote.—There should have been ‘an ac- 
count kept of the carbonic acid gas which was 
produced.—In a well made experiment nothing 1s 
either lost or gained: whenever, therefore, the weight 
of the product and of the residuum does not cor- 
respond with the weight of ‘the substances from 
which they came, there must be an error, This is 
the case with these few experiments. They can 
then surely not be put in competition with the many 
experiments on which the new theory rests, and which 
have been made with the most’ scrupulous exact- 
ness, with substances of the greatest purity, and in 
circumstances which leave no room for any reason- 
