Full text: Vol. II (2)

CHARCOAL 
200 
tort and nitre begin to be ignited, the vital air begins to come forth. 
At the first it is very pure, provided the nitre be quite free from dust 
or admixture of vegetable or animal matter. If such matter be pre 
sent in it, though in exceedingly small quantity, some carbonic acid 
gas is formed at first, and comes out mixed with the first portions of 
vital air and some azote. After this, or from the beginning, if the 
nitre was quite pure, we obtain a great quantity of good vital air, 
which, if not quite pure, contains a fmall admixture of azotic gas. 
But, towards the end of the operation, when the heat must be in 
creased to a higher degree, the vital air comes over mixed with a more 
considerable portion of azotic gas. The reason of this difference in 
the purity of the vital air is, that in the beginning, the nitric acid 
gives out only a part of the oxygen which it contains, (nearly ) 
and in this 
and it is changed into nitrous acid, retaining perhaps 
ſtate continues adhering to the alkalis. In the nitrous acid, therefore, 
there is a deficient proportion of oxygen, and a superfluous quantity 
of azote. When the proceſs is continued, and the heat increased to 
produce a more complete decomposition of the acid, the azote must 
neceſſarily make its appearance in a proportion continually increafing. 
All theſe facts, and many more, to be mentioned as we proceed, 
and which are fo well explained by Mr. Cavendifh’s discovery, con 
firm the solidity of that discovery, making it one of the most impor 
tant which the modern chemistry has produced. 
One of the moît remarkable properties of charcoal, when recently 
taken from the fire, is an attraction for a certain quantity of humidity, 
and for various odorous and colouring matters of different fluids, con 
taining animal or vegetable substances, subject to fermentation or cor 
ruption,—as also for the acetous acid. 
We have proofs of its attraction for humidity in many curious ex 
periments of Mr. Scheele and Dr. Priestley. Although indestructible 
by heat in close vessels without addition, yet, if moistened, it will yield 
carbonic acid and hydrogenous gas. This may be repeated by an¬
	        
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