122 
hundred years before Priestley’s time, 
Borch (1678) prepared what is now known 
as oxygen in large quantities by heating 
saltpeter, but he failed to ascertain any of 
its properties; and again, forty-five years 
before Priestley’s experiment, Hales col- 
lected the gas from the same source over 
water (the first record of any attempt to 
collect a gas in this way) and obtained, by 
measurement, 97 per cent. of the theoret- 
ical amount. But Priestley, on August 1, 
1774, liberated it from mercuric oxide. A 
lighted candle happened to be standing be- 
fore him at the moment. By pure chance, 
as he himself says, and without any par- 
ticular reason which he could afterwards 
recall, he immersed the candle in the gas 
and found that the combustion was un- 
usually brilliant! He thus ascertained one 
distinct property of the substance and be- 
came the discoverer of oxygen. ‘True, he 
thought at first that it was a compound of 
nitrous acid, earth and phlogiston, and 
only in the light of the views of Lavoisier 
and others, and after long delay, did he 
aecept in 1786 the conclusion that it was 
an elementary substance. It may be noted 
that, although Scheele was a better ex- 
perimenter, his idea of the nature of oxy- 
gen was not much clearer. He thought 
that fire-air (oxygen) united with phlogis- 
ton to give heat, and that the last was a 
compound of the first two. Evidently, in 
those days, isolating the substance, and de- 
fining one or two of its properties, to- 
gether conferred discoverer’s rights, no 
matter how grotesquely the nature of the 
substance was misunderstood. 
I say “‘in those days,’’ for Curie made 
several compounds of radium, establishing 
their relations to one another, and is justly 
held to be the “‘discoverer of radium,’’ 
although no isolation of the element was 
attempted. Now that the science has de- 
veloped, isolation can be dispensed with, 
SCIENCE 
[N.S. Vou. XXXV. No. 891 
and, in point of fact, was omitted in most 
of the exploratory work amongst the rare 
metals. If this principle could have been 
applicable in earlier days, several of the 
decisions of chemical history might have 
been reversed. A hundred years before 
Priestley’s time, Mayow (1669) had shown 
by conclusive experiments that atmos- 
pheric air was made up of two components, 
of which the active one formed twenty-five 
per cent. of the whole. In measuring the 
amount, he employed the same reaction 
subsequently used by Priestley, namely, 
removal of the oxygen by the introduction 
of nitric oxide and absorption of the prod- 
uct in water. But whereas Priestley was 
thereby estimating the ‘‘goodness’’ of the 
air, and had no idea that he was dealing 
with a mixture, Mayow was perfectly clear 
as to the interpretation of the results. The 
latter demonstrated that the same com- 
ponent was removed in combustion, by 
rusting metals, by the alcohol in vinegar- 
making and by the blood in respiration. 
He traced the animal heat of the body to 
a process analogous to that which heated 
the mass when marcasite rusted in the air. 
He identified this active component of the 
air as a constituent of saltpeter, and par- 
ticularly of the acid part of this substance, 
and (like Lavoisier more than a century 
later) held that it was contained in all 
acids. Finally, he considered it to be an 
element, in the modern sense of the word. 
Unfortunately circumstances conspired to 
relegate to obscurity all his wonderful 
work and magnificently clear reasoning. 
Mayow was a young physician, and the 
divergent view-point of Boyle, as an older 
man and an eminent philosopher, received 
more attention. Again, the logical con- 
clusiveness of Mayow’s proof of the exist- 
ence of oxygen as a distinct substance, was 
entirely over the heads of his contempora- 
ries, and his way of thinking quite out of 
