[68] Here it is necessary to observe, for the sake of accuracy and perspicuity, that, in the new chemistry, the terms of which are now very generally adopted, the words oxygen and hydrogen when mentioned by themselves are not understood to signify any kind of air, but what I have called the condensable part of the air. If the word air is added, then the whole substance of the fluid is understood. But though this is the strict orthodox language of the new chemistry, it is impossible to say whether every one who adopts the terms be sufficiently careful in this respect. Indeed this is one out of many inconveniences that might be pointed out which have arisen from this nomenclature; for thus the mere omission of a monosyllable, which may happen in numberless instances, totally perverts the meaning of the author, and may of course subject him to unmerited censure. Besides, it is not to be known, unless the author tells us so, that he designs to observe this strictness, and of consequence we must in multitudes of cases be uncertain of the meaning of what we read. Thus, in the present instance, when Dr. Girtanner speaks of oxygen, we know not certainly whether he means the air in substance, or only one of its component parts. Probably he means the condensable or solid part. If he does so, there must be a very material difference between his theory and that laid down in the Encyclopædia, and which is supported throughout this treatise. In the latter it is maintained that the condensable part is thrown out by the breath, being previously converted into fixed air, while the elastic part enters the vital fluid, communicating to it not only the red colour, but heat, and the principles of life and sensation, as will be more fully explained in the sequel.
[69] Hydrogen air is the same with that by Dr. Priestley called inflammable air. He also discovered the true composition of it. Having included a few grains of charcoal in the receiver of an air-pump, and exhausted the air, he heated it in vacuo by means of a large burning glass. The charcoal was entirely volatilized and converted into this kind of air. He found, however, that without some small portion of moisture this volatilization did not take place.
[70] A glass tube is sealed hermetically, by heating the open end or ends, till they become soft, and then closing them with a pair of pincers.
[71] Thus letters, or other characters, may be curiously marked upon the calx within the vial, by cutting them out in paper, and then pasting them on the side to be exposed to the light. We may have them in this manner either dark upon a white ground, or white upon a dark ground.
[72] It is now acknowledged that common atmospherical air contains a portion of what Dr. Black and Dr. Priestley have called fixed air; but this portion is so small (not more than one fiftieth part, according to Dr. Anthony Fothergill’s Prize Dissertation, and none at all, according to Dr. Beddoes) I say, this proportion is so small, that we cannot suppose it to constitute the quantity of fixed air thrown out by the breath, which is very considerable. Besides, fixed air, of all others, is the most readily absorbed; and, indeed, if we could admit of absorption of any basis of air in the present case, it certainly ought to be that of fixed air; but where such a quantity is thrown out, we cannot well admit of any absorption.
[73] Nitrous air is that suffocating vapour which arises when aqua fortis is poured upon metals. When taken into the lungs it destroys animal life more quickly than any other species.
[74] In one of Dr. Priestley’s papers above quoted he says, that charcoal is entirely of vegetable origin; but the conversion of vegetable into animal matter which we daily see is an undoubted proof that there cannot be any essential difference between them. Even the bones are undoubtedly produced from vegetables in such animals as feed upon vegetable substances; so that even the calcareous earth they contain is plainly of vegetable origin. We may say indeed that the calcareous particles had a previous existence in the vegetables used by the animal as food; but we may say the same of the particles of the blood, flesh, horns, &c. Besides, Dr. Priestley has shown that every particle of charcoal may be volatilized into inflammable air, with as great accuracy as any human experiment can be made; so that in this case the calcareous particles, if any such there were, showed themselves to be as much charcoal as the rest. In the 74th volume of the Philosophical Transactions, Mr. Watt has shown, that dephlogisticated spirit of nitre may be changed into the smoking and phlogisticated kind by means of red-lead or magnesia alba, as well as by charcoal; of consequence there can be no essential difference even there. In short, so wonderful and multifarious are the transforming or metamorphosing powers of nature, that every attempt to find out a substance upon which these powers cannot act, will be found altogether vain, and our best conducted and most plausible experiments, made with a view to discover the ultimate composition or what we call the elements of bodies, will be found mere inaccuracy, bungling and blunder.
[75] These words are to be found in the M. S. Copies of his lectures circulated at Edinburgh. Dr. Black himself never published any thing to the world upon the subject.
[76] Monthly Review, for 1790, p. 165.
[77] Count Rumford was superintendant of boring the cannon in the workshops of the military hospital at Munich.