VOL. LXIX.] PHILOSOPHICAL TRANSACTIONS. 541 



When I consider, (says Dr. I.), the immense quantity of this pure aerial fluid, 

 called by Dr. Priestley with so much propriety dephlogisticated air, which exists 

 as it were in a solid state in nitre, in calcined metals, and even in some other of 

 the most common substances, I cannot express the greatness of my expectation, 

 as a physician, from such an important discovery.* I flatter myself, that ere 

 long an easy and cheap method will be discovered, by which such quantities of 

 this beneficial air may be obtained as will serve to cure several diseases which 

 resist the power of all other remedies, and so prolong, as it were, human life. 

 We may expect, with some degree of confidence, that this new element, when 

 it shall be used for the benefit of respiration, will be found more fit than the 

 best common air to free our body from that quantity of phlogiston or in- 

 flammable principle which seems to exist sometimes in too great a quantity in the 

 mass of our blood; or from which it seems sometimes, as it were, to be let 

 loose in too great abundance, producing perhaps in consequence fevers and other 

 symptoms, the causes of which have not yet been clearly elucidated by the best 

 medical writers. 



This dephlogisticated air, free from the inflammable particles with which the 

 best common air is always infected, will probably be found capable of absorbing 

 a greater quantity of those phlogistic particles with which the air coming from 

 our lungs is found to be pregnant, and thus of ventilating, as it were, much 

 more expeditiously the mass of our blood of that which a constant exertion of 

 the organs of respiration is not always able to free it from in a sufiicient 

 quantity. These important pursuits have led Dr. Priestley to the discovery of 

 one of the benefits, and perhaps the principal, that we derive from respiration; 

 that function of the animal economy which is so important, that without its 

 constant influence an animal, once born, has but a few moments to live. 



The criterion of the degree of goodness of respirable air, by the quantity 

 which is absorbed or destroyed by the addition of nitrous air, is one of those 

 useful discoveries of Dr. Priestley's from which mankind will, perhaps, hereafter 

 reap a considerable benefit. The discovery of the various kinds of inflammable 

 airs or gases becoming powerfully explosive, when they are mixed with a suffi- 

 cient quantity of common air, and still more so when they are combined with 

 dephlogisticated air, is one of those improvements in natural philosophy which, 

 giving occasion to various amusing and interesting experiments, have cast at the 



* Since Dr. Priestley's last publication on air, he discovered, that the same water which, if 

 examined immediately, gives only a small quantity of bad air, yields spontaneously about 10 times 

 the quantity of pure dephlogisticated air after standing some time exposed to the sun. Of this I was 

 an eye-witness. The important discoveries of Abbe Fontana on this subject, which he showed me 

 when I was last in Pans a year and a half ago, will soon be published by himself. He extracted this 

 wonderfvil aerial fluid from different kinds of water by boiling them over a fire. — Orig. 



