PRESIDENTIAL ADDRESS. 117 
capable of supporting either life or combustion. The portion 
which is necessary for life enters, during respiration, into 
the blood. It is the chief cause of motion in animals and 
in plants.” (See Ramsay.) 
These “nitro-aerial particles’ he also finds in saltpetre 
or nitre. 
Both Boyle and Mayow reached very near the truth. 
They had a wide grasp of their subject, and their works are 
full of shrewd observations and well-devised experiments. 
Black had discovered or rediscovered fixed air (1755) 
(carbon dioxide), examined its properties, fixed it with 
caustic alkalies, and made use of the balance in his imvestiga- 
tion. He knew that this “air” or “ gas,” that could be 
fixed as a solid carbonate, was the same as that given off by 
the lungs, by combustion, found naturally at the Grotto del 
Cane and similar places, given off by mineral springs, and 
resulting from certain fermentations. 
Rutherford, in 1772 (apparently anticipated by Scheele), 
isolated nitrogen (mephitic air, phlogisticated air, spent air) 
by absorbing the carbon dioxide produced by respiration or 
combustion in a confined space of air, finding the residue im- 
capable of supporting respiration or combustion. 
_ Nitrogen appears to have been isolated and examined in- 
dependently by Cavendish. 
Priestley, in 1774 (and Scheele, according to recent dis- 
closures, somewhat earlier—1772), isolated oxygen by heat- 
ing mercury oxide, and studied the properties of this oxygen 
(dephlogisticated air, fire air, life air), finding it possessed 
of increased power of supporting respiration and combustion. 
They both knew that atmospheric air consisted of a mixture 
of these two gases. Another significant fact elicited was 
that a candle burning i a confined space of air produced an 
amount of fixed air (carbon dioxide) exactly equal in volume 
to the amount of oxygen that had disappeared. 
Lavoisier (1743-1794), in his ever-memorable researches, 
collected the results of the phlogistonists, repeated some of 
their experiments, and above all made an appeal to the 
balance. 
He caused the oxygen in a given volume of air to combine 
with mercury as oxide of mercury, measured the diminution 
in volume, weighed the oxide of mercury produced, extracted 
the oxygen from it by heat, and found its volume to equal 
the volume lost by the air (about 4 of the original volume). 
‘Lavoisier thus removed the oxygen from the air, isolated it, 
-and examined its properties. 
