Experiments and Observations on Different Kinds of Air. Joseph Priestley

Sect. X. Miscellaneous Observations 154 PART II. Experiments and Observations made in the Year 1773, and the Beginning of 1774. Sect. I. Observations on Alkaline Air 163 Sect. II. Of common Air diminished, and made noxious by various processes 177 Sect. III. Of Nitrous Air 203 Sect. IV. Of Marine Acid Air 229 Sect. V. Of Inflammable Air 242 Sect. VI. Of Fixed Air 248 Sect. VII. Miscellaneous Experiments 252 Sect. VIII. Queries, Speculations, and Hints 258 The APPENDIX. Number I. Experiments made by Mr. Hey to prove that there is no Oil of Vitriol in water impregnated with Fixed Air 288 Number II. A Letter from Mr. Hey to Dr. Priestley, concerning the effects of fixed Air applied by way of Clyster 292 Number III. Observations on the Medicinal Uses of Fixed Air. By Thomas Percival, M. D. Fellow of the Royal Society, and of the Society of Antiquaries in London 300 Number IV. Extract of a Letter from William Falconer, M. D. of Bath 314 Number V. Extract of a Letter from Mr. William Bewley, of Great Massingham, Norfolk 317 Num. VI. A Letter from Dr. Franklin 321 Number VII. Extract of Letter from Mr. Henry of Manchester 323

THE INTRODUCTION.

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SECTION I.

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A general view of preceding discoveries relating to air.

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      For the better understanding of the experiments and observations on different kinds of air contained in this treatise, it will be useful to those who are not acquainted with the history of this branch of natural philosophy, to be informed of those facts which had been discovered by others, before I turned my thoughts to the subject; which suggested, and by the help of which I was enabled to pursue, my inquiries. Let it be observed, however, that I do not profess to recite in this place all that had been discovered concerning air, but only those discoveries the knowledge of which is necessary, in order to understand what I have done myself; so that any person who is only acquainted with the general principles of natural philosophy, may be able to read this treatise, and, with proper attention, to understand every part of it.

      That the air which constitutes the atmosphere in which we live has weight, and that it is elastic, or consists of a compressible and dilatable fluid, were some of the earliest discoveries that were made after the dawning of philosophy in this western part of the world.

      That elastic fluids, differing essentially from the air of the atmosphere, but agreeing with it in the properties of weight, elasticity, and transparency, might be generated from solid substances, was discovered by Mr. Boyle, though two remarkable kinds of factitious air, at least the effects of them, had been known long before to all miners. One of these is heavier than common air. It lies at the bottom of pits, extinguishes candles, and kills animals that breathe it, on which account it had obtained the name of the choke damp. The other is lighter than common air, taking its place near the roofs of subterraneous places, and because it is liable to take fire, and explode, like gunpowder, it had been called the fire damp. The word damp signifies vapour or exhalation in the German and Saxon language.

      Though the former of these kinds of air had been known to be noxious, the latter I believe had not been discovered to be so, having always been found in its natural state, so much diluted with common air, as to be breathed with safety. Air of the former kind, besides having been discovered in various caverns, particularly the grotta del Cane in Italy, had also been observed on the surface of fermenting liquors, and had been called gas (which is the same with geist, or spirit) by Van Helmont, and other German chymists; but afterwards it obtained the name of fixed air, especially after it had been discovered by Dr. Black of Edinburgh to exist, in a fixed state, in alkaline salts, chalk, and other calcareous substances.

      This excellent philosopher discovered that it is the presence of the fixed air in these substances that renders them mild, and that when they are deprived of it, by the force of fire, or any other process, they are in that state which had been called caustic, from their corroding or burning animal and vegetable substances.

      Fixed air had been discovered by Dr. Macbride of Dublin, after an observation of Sir John Pringle's, which led to it, to be in a considerable degree antiseptic; and since it is extracted in great plenty from fermenting vegetables, he had recommended the use of wort (that is an infusion of malt in water) as what would probably give relief in the sea-scurvy, which is said to be a putrid disease.

      Dr. Brownrigg had also discovered that the same species of air is contained in great quantities in the water of the Pyrmont spring at Spa in Germany, and in other mineral waters, which have what is called an acidulous taste, and that their peculiar flavour, briskness, and medicinal virtues, are derived from this ingredient.

      Dr. Hales, without seeming to imagine that there was any material difference between these kinds of air and common air, observed that certain substances and operations generate air, and others absorb it; imagining that the diminution of air was simply a taking away from the common mass, without any alteration in the properties of what remained. His experiments, however, are so numerous, and various, that they are justly esteemed to be the solid foundation of all our knowledge of this subject.

      Mr. Cavendish had exactly ascertained the specific gravities of fixed and inflammable air, shewing the former of them to be 1–½ heavier than common air, and the latter ten times lighter. He also shewed that water would imbibe more than its own bulk of fixed air.

      Lastly, Mr. Lane discovered that water thus impregnated with fixed air will dissolve a considerable quantity of iron, and thereby become a strong chalybeate.

      These, I would observe, are by no means all the discoveries concerning air that have been made by the gentlemen whose names I have mentioned, and still less are they all that have been made by others; but they comprise all the previous knowledge of this subject that is necessary to the understanding of this treatise; except a few particulars, which will be mentioned in the course of the work, and which it is, therefore, unnecessary to recite in this place.

SECTION II.

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An account of the apparatus with which the following experiments were made.

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      Rather than describe at large the manner in which every particular experiment that I shall have occasion to recite was made, which would both be very tedious, and require an unnecessary multiplicity of drawings, I think it more adviseable to give, at one view, an account of all my apparatus and instruments, or at least of every thing that can require a description, and of all the different operations and processes in which I employ them.

      It will be seen that my apparatus for experiments on air is, in fact, nothing more than the apparatus of Dr. Hales, Dr. Brownrigg, and Mr. Cavendish, diversified, and made a little more simple.