William Ramsay

“ When steam is formed by the union of hydrogen with oxygen, it has a volume equal not to the sum of the volumes of the hydrogen and the oxygen, but to two-thirds of the sum, or equal to that of the hydrogen alone, or twice that of the oxygen. And as steam, like hydrogen and oxygen, follows Boyle’s and Gay-Lussac’s laws, it must be supposed that in the steam there are as many particles as in the hydrogen from which it was formed. But the particles of steam must necessarily be more complex than those of the hydrogen, inasmuch as the steam contains oxygen as well as hydrogen. ”

“ There is no power in Nature from which nothing could have made the universe, and none which could reduce the universe to nothing: that requires the same virtue. Now the matter would be otherwise if there could be a vacuum. ”

“ Before leaving the seventeenth century, it is perhaps fitting to mention the name of Jean Rey, a French physician, who wrote in 1630 concerning the gain in weight of tin and lead when calcined. While Rey exhibited some leaning towards the modern methods of experimentation, he still lay fettered in the bonds of mediæval scholasticism. In discussing the weight of air and fire, he finds occasion to consider the question whether a vacuum can exist. His words are so quaint that they are worth quoting: “It is quite certain that in the bounds of Nature a vacuum, which is nothing, can find no place. ”

“ The Schools teach the air to be a warm and moist element, and consequently a simple and homogeneous body. Many modern philosophers have, indeed, justly given up this elementary purity in the air, yet few seem to think it a body so greatly compounded as it really appears to be. The atmosphere, they allow, is not absolutely pure, but with them it differs from true and simple air only as turbid water from clear. ”

“ It is indeed astonishing that men of such great ability and acumen as Black and Cavendish should have so long lain under the yoke of this absurd theory. It is probable that, in the case of these two great chemists, they stated their results in terms of the theory, partly because they were content to express the facts to which they wished to call attention in this manner, partly because they were not in a position to replace the theory by a more rational one. It is not easy to revolutionise a language, even though its vocabulary be a restricted one. ”

“ Heat is one form of energy, and it is measured by an interval of [Pg 235] temperature, and by a property which we term specific heat. It happens that the latter property varies, not with the mass of the substance heated, but with its atom, so that all elements have approximately the same atomic heat; that is, quantities of elements proportional in mass to their atomic weights require approximately equal increments of heat to raise their temperature through an equal interval, say 1°. This is the formulation of Dulong and Petit’s law previously alluded to. ”

“ There is no known reason why mass and weight should be proportional to each other; for the cause of the attraction of the earth has never been satisfactorily elucidated. We therefore use weight, or the attraction of the earth, as a convenient means of determining the relative masses of two objects. ”

“ Many men talk much of a volatile nitre in the air, as the only salt wherewith that fluid is impregnated. I must own the air, in many places, seems to abound in corpuscles of a nitrous nature; but I don’t find it proved by experiments to possess a volatile nitre. In all my experiments upon salt-peter, I found it difficult to raise that salt by a gentle heat; and spirits of nitre, which is drawn by means of a vehement one, has quite different properties from crude nitre, or the supposed volatile kind in the air, for ’tis exceeding corrosive. ”

“ Oxygen was thus successfully separated from air, and obtained from it in a pure condition for the first time, in a single series of operations.
In Lavoisier we see a master mind, not only capable of devising and executing beautiful experiments, but of assimilating those of others, and deducing from them their true meaning. Although his additions to the known chemical compounds were few in number, and cannot be compared with those of Scheele or of Priestley, yet his reasoning in disproof of the phlogistic theory was so accurate and so exact that it rapidly secured conviction. ”

“ The heat imparted to an aggregation of atoms is not expended solely in raising their temperature; other work is done also, as is generally supposed, in the nature of expansion, or separation of parts, as in overcoming the attraction between the atoms in the molecule, or in imparting special motion to the atoms; such work, however, involves an expenditure of energy which is either very small in proportion to the total energy imparted as heat, or is nearly the same for all elements. ”

“ His view of the nature of this gas, in the phlogistic language of the time, was that the burning bodies had given up some of their “phlogistic material” to the air, which was thus altered. Nitrogen was “phlogisticated air,” even though incombustible; hydrogen, too, was phlogisticated air, but air produced by the union of pure phlogiston with atmospheric air. The step taken by Rutherford, under Black’s guidance, was an advance, though not a great one, in the development of the theory of the true nature of air; and he may be well credited with the discovery of nitrogen. ”

“ The density of mercury gas is 100, and its molecular weight must be 200. But if its atomic weight is also 200, it follows of necessity that its molecule and its atom must be identical; that unlike oxygen and hydrogen, its molecule consists, not of two atoms, but of one single atom. There is nothing strange in this conclusion; there is [Pg 198] no evident reason why single atoms should not act as molecules, or independent particles, able to exist in a free state, uncombined with each other or with any other molecules. ”

“ Some burning bodies deprive air of its “salubrity” more easily than others. The phosphorus of urine continues to glow in air in which a candle has ceased to burn, or in which charcoal has burned until it is extinguished. Even after the absorption of all fixed air by alkalies, phosphorus burns, emitting clouds of the dry acid of phosphorus, which can be absorbed by lime-water.
“It therefore appears that pure air is not converted into mephitic air by force of combustion, but that this air rather takes its rise or is thrown out from the body thus resolved. ”

“ Boyle’s discovery that if the pressure on a gas be increased, the volume of the gas, whatever it may be, diminishes in like proportion; and (2) Gay-Lussac’s and Dalton’s discovery, that all gases, when equally raised in temperature, expand equally. It would be very remarkable if one gas, containing twice as many particles in unit volume as another, should show exactly similar behaviour towards pressure and temperature. Hence it appeared not unreasonable to suppose that the composition of water was expressed by one particle of oxygen in union with two particles of hydrogen. ”

“ Scheele defines air. It is that fluid invisible substance which we continually breathe; which surrounds the whole surface of the earth, is very elastic, and possesses weight. “It is always filled with an astonishing quantity of all kinds of exhalations, which are so finely divided in it that they are scarcely visible, even in the sun’s rays.” [11] It also contains another elastic substance resembling air, termed aerial acid by Bergman (identical with Black’s fixed air) . ”

“ A piece of musk retains its fragrant odour for years, and the most delicate balance fails to detect any appreciable loss of weight in it. We are capable of smelling gases only: liquids and solids, if introduced into the nostrils, irritate the olfactory nerves, but do not stimulate them so as to incite the sense of smell; yet the admixture of a minute trace of some odorous vapour with air appears entirely to change its properties. ”

“ It has been necessary to enter at some length into the nature of the phlogistic theory, because the discoveries of the time were expressed in its language. The fire-air or vital air of Mayow was termed dephlogisticated air; i.e. air wholly deprived of the power of burning, or air more capable of supporting combustion than ordinary air; while airs capable of burning were supposed to be more or less highly charged with phlogiston; indeed, at one time, it was imagined that hydrogen was phlogiston itself. ”

“ Since an atom of an element is defined as the smallest amount which can exist in combination, then, if numerous compounds of an element be examined, that one which contains proportionally the least amount of the element may be regarded as containing an atom, unless there are reasons to the contrary. For example, reverting to the former instance of water, the relative proportions by weight of oxygen and hydrogen are, in round numbers, 16 to 2. Reasons have already been given showing why its formula should be H2O and not HO; its molecule must contain two atoms of hydrogen. ”

“ It appears certain that, on raising the temperature of argon, very little, if any, energy is absorbed in imparting vibrational motion to its molecules; and our choice lies between our ability or inability to conceive of a molecule so constituted as to be incapable of internal motion. If there be any truth underlying Professor Boltzmann’s conception, a molecule of argon cannot consist of any complex structure of atoms, otherwise it would possess more than three degrees of freedom, and heat would be utilised in causing rotational motions. ”

“ We now know that air will not support life of warm-blooded animals when the oxygen falls below a certain not very small amount, while insects appear to be capable of exhausting the oxygen to a great extent; and it is probable that the plants, under the unnatural circumstances in which they were placed, gave off a considerable amount of carbon dioxide. Scheele’s explanation in terms of phlogiston is not successful. He wrote:—“I am inclined to believe that fire-air consists of a subtle acid substance united with phlogiston, and it is probable that all acids derive their origin from fire-air. ”

“ The ammonia, small though its proportion is, plays a great part, although not an exclusive one, in yielding to plants their supply of nitrogen. The rain, percolating through the soil, leaves the ammonia behind, in some [Pg 149] form of combination; and it is then attacked by the nitrifying ferments and converted into nitrates, from which the plants derive the nitrogen which forms part of their substance, in combination with carbon, oxygen, and hydrogen.
There are also traces of nitric and nitrous acids in air, which are apparently in combination with ammonia. ”

“ In this he showed that oxygen gas is the only substance which supports [Pg 111] combustion; that during the burning of combustible substances in air a portion of the oxygen disappears, and converts the burning substance into one of two kinds of compounds: either an acid, such as sulphuric acid from sulphur, phosphoric acid from phosphorus, or carbonic acid from carbon (for in those days the term “acid” was applied to what we now term an anhydride) ; or in the case of metals a calx, or compound of oxygen with the metal. ”

“ The object of science, as indeed of inquiry in all departments of human interest, is to reconcile the world of man with the world of nature, and to endeavour to know in part that of which we hope one day to attain to a perfect knowledge. ”

“ And as the history of the discovery of the better known constituents of the atmosphere is of itself of great interest, and leads up to an acquaintance with the new stranger, who has so long been with us incognito, an effort has here been made to tell the tale of the air in popular language. ”