57 
EXPERIMENT XL 
A third was surrounded by hydrogen air, to which was added a portion 
of oxygen air . 
EXPERIMENT XXL 
A fourth was in hydrogen air , to which was added only a portion or 
common atmospheric air. 
EXPERIMENT XIII. and XIV. 
The same thing was done by the air corrupted hy breathing as in the 
two last experiments. 
EXPERIMENT XV. 
A seventh was placed in common air. 
EXPERIMENT XVI. 
And the last was in oxygen air of 300* degrees of purity. 
the air passing oyer the ramification of the blood-vessels in the lungs is decomposed. Oxygen air is 
absorbed by the blood, and at each expiration there is fixed air thrown out with water, and the resi¬ 
duary azot, which acts chiefly as a vehicle or alloy to the oxygen air, wdiich now passes into the 
blood. 
* The degree of goodness of any air is ascertained by means of an instrument called an Eudio¬ 
meter, the invention of Dr. Priestley, which is a long glass tube graduated, containing the air you 
wish to examine. This is inverted over water, and examined by the means of nitrous air. This air 
was the fortunate discovery of Dr. Priestley, who produced it by pouring the nitrous acid on copper 
or any other metal, when a dissolution of the metal takes place, and the oxygen of the nitrous acid, 
uniting with the metal to which it has a greater affinity than for its own base, calcines it, leaving the 
nitrous air free, which ascends in its aerial form. Now this air, when it meets with oxygen air, from 
the law of affinity, to which it is subject, quickly unites with it, and is reconverted into the state of 
nitrous acid. This is, says Dr. Priestley, one of the most astonishing experiments in chemistry. 
When you pour vitriolic acid on marble you are surprised to find torrents of fixed air issue from the 
solid body. Here you see two airs occupying considerable bulk, when coming into contact, instead 
of being as before diaphanous, now assume a red colour, and seize upon and devour each other in such 
a way, that they soon occupy an inconsiderable space; and one measure of this air will destroy four 
of oxygen, when it becomes nitrous acid, which is absorbed by the water as it rises up the tube. 
Nitrous acid attacks no other air than oxygen air, because it has no affinity for any other than this; 
and hence it discovers the quantity of oxygen air in any given volume of air, and thus becomes the 
test of the purity of any air which we know to depend upon the quantity of oxygen air it contains. 
P 
