GRAHAM LECTURE.

VII.-On Argon and Helium. By Professor WILLIAM RAMSAY, Ph.D., F.R.S., University College, London, and a former Member of the Society.

[Delivered to the Society, 8th January, 1896.]

(WITH EIGHT PAGE ILLUSTRATIONS.)

IN beginning my lecture on this subject, it may not be inopportune to say a few words about the early history of air, seeing that what I have to deal with later on has reference to one constituent of the atmosphere of the earth, and to a constituent of the atmosphere of the sun and the stars. In the early history of air it was supposed to be an element; but the word "element" in those days did not always bear the signification which we now give to it. Sometimes it was used in the sense in which we now employ it, as a constituent of a compound substance, and sometimes it was employed in the sense of a quality or property of bodies. These two meanings were much confused. Some writers used the word in one sense, some in the other, and some mixed both senses in their writings. A summary of the creation of the world, according to the old idea, is given in a poem by Lucretius, "De Rerum Natura," or "The Nature of Things," and I quote from him these lines, which seem to convey pretty nearly the ancient ideas concerning air

"Denique res omnes debent in corpere habere,

Aera quandoquidem rara sunt corpora et aër,
Omnibus est rebus circumdatus appositusque."

"The air surrounds and is in contact with everything, and is a constituent of all bodies, inasmuch as all bodies are porous or of fine texture."

These views met their first opposition from Boyle, who, in the reign of Charles II., published an essay, termed "Memoirs for a General History of the Air." Boyle's style is very discursive, but, fortunately, there is left to us an exact summary of his views regarding air. His words are "I conjecture that the atmospheric

air consists of three different kinds of corpuscles: the first, those numberless particles which, in the form of dry exhalations or vapours, ascend from the earth, water, minerals, vegetables, animals, etc.; in a word, whatever substances are elevated by the celestial or subterraneal heat, and thence diffused into the atmosphere. The second may be yet more subtile, and consist of those exceedingly minute atoms, the magnetical effluvia of the earth, with other innumerable particles sent out from the bodies of the celestial luminaries, and causing, by their impulse, the idea of light in us. The third is its characteristic and essential property-I mean, permanently elastic parts." Those were once the ideas of an able thinker concerning the very complex nature of air. I show you Boyle's portrait on the screen.

We come next in order of time (or rather contemporaneously) to John Mayow, whose portrait I also show you. Mayow was a medical man who practised at Bath during the Bath season. He was a native of Oxford, or, at all events, was educated there. His views were much more advanced than those of Boyle. He recognised that the air contained certain particles, as he called them, to which he gave the name of nitro- or igneo-aërial particles, or, as we may translate that term, fire-air particles. These particles were substantially what we now know as oxygen. He recognised that air was composed of two distinct things, one of which was capable of supporting combustion, while the other was left behind after the burning bodies had removed particles of the first kind. The portion which was left behind he termed mephitic air, or air injurious to life and incapable of supporting combustion. I am fortunate in being able to show you a portrait of Mayow. He died at the early age of 32 years. Had he lived, no doubt he would have anticipated by more than a century the discoveries of the great French chemist, Lavoisier. It must be remembered that Boyle did not accept Mayow's views, although he knew of their existence. He was 58 years of age when Mayow's tractate was published, and a man of mature years is sometimes not disposed to be very charitable to a young man of 32, who airs certain views which are subversive of all old doctrines, and which are supposed not to be supported by sufficient experimental evidence.

Later on, about the year 1720, we come to the third investigator of air, Stephen Hales. You will notice, perhaps, that all those names are English. The discoverers in connection with air, curiously enough, have been almost entirely of English or of

Scottish extraction. Hales was a clergyman who amused himself with botany and horticulture, and who made experiments with vegetables; and having noticed that they evolved air when placed under an air-pump, he experimented on it. In other ways he attempted to extract air from vegetables by distilling them, and having got what he supposed was air by that method, he distilled a great many other substances. He was very careful to give data showing the volume of air which he got from known weights of the substances distilled. After several hundred such experiments he wrote "Whence it is reasonable to conclude that our atmosphere is a chaos, consisting not only of elastic, but also of inelastic air particles, which float in it, as well as sulphureous, saline, watery, and earthy particles." The word 'sulphureous" must be understood in the sense of those days as meaning "capable of burning."

The first definite discovery as regards the nature of air was made by a Scotsman, a former Lecturer on Chemistry in Glasgow University, and subsequently Professor in Edinburgh University, Joseph Black. He applied heat to what was then a new compound, carbonate of magnesium, from which he got a particular kind of air, which we know now as carbonic acid gas, or carbon dioxide. He found that this new "air was capable of being fixed in combination with alkalies or lime; therefore, he called it "fixed air." He made it very clear that this air was not of the same kind as ordinary atmospheric air. I think he may be said to have been the first to point out that it is possible to prepare different kinds of air, and that they are not all modifications of atmospheric air, but that they have as much right to be called separate substances as any substance which we can handle or touch.

After Black came one of his pupils, Daniel Rutherford, afterwards Professor of Botany in Edinburgh University, who, for his inaugural dissertation for the M.D. degree, as he states, by Black's advice, undertook researches into the residue which was left after a candle, or charcoal, or similar combustible bodies, had been burned in air. After burning charcoal, for example, he found that if air was shaken up with lime-water or with alkali, the fixed air was removed; and that having removed this fixed air, a residue was left. This residue we now know as nitrogen. It was recognised as differing from ordinary air, inasmuch as it would not support combustion; and as differing from fixed air or carbonic acid,

inasmuch as it was not absorbable by alkalies. The views of philosophers in those days were what we should now term "topsyturvy," or reversed. It was imagined that bodies capable of burning gave up something during their combustion; it was not recognised that they absorbed oxygen from the air. It was supposed that they lost something of the nature of flame, and to that "something" was given the name phlogiston. It was the "principle of burning" which they lost by being burned, so that they were no longer capable of being burned. Rutherford noticed that such substances as charcoal, or a candle, or lead, when heated in air, became changed, and that they were no longer capable of burning, and he imagined that they had given to the air this substance, phlogiston, which they themselves had lost. Hence he called this residue, which was left after the candle was burned in the air, "phlogisticated air." This "phlogisticated air" is what we now know as nitrogen.

Passing from Rutherford, we come next in order of time to Joseph Priestley, who was born near Leeds, and who was a Unitarian minister in Birmingham for many years. His publications related chiefly to controversial subjects in the domain of theology, but in the intervals of writing his controversial pamphlets he amused himself in his laboratory. He was first led to make experiments by his neighbourhood to a brewery in Leeds. His church was just alongside the brewery, and after preparing his sermons he took exercise in the brewery, and experimented on the air which came from the vats. This led him to the investigation of various kinds of gases, and he was the first to succeed in isolating the gas oxygen; and recognising that it, too, was distinct from ordinary air, he imagined it to be good air, and his works are full of the "goodness" of that air-what would now be termed the percentage of oxygen in the air. He obtained oxygen by heating red oxide of mercury, and also red-lead. Thirty years before, Hales was content to compare the weight of the lead compound with the volume of the oxygen got from it; but he does not seem to have made any experiments as to whether this gas was a separate constituent, "better" than ordinary air. It was Mayow's igneo-aërial particles to which Priestley gave the name vital air. He was acquainted with Rutherford's work at the time, for he refers to his experiments.

Contemporaneous with Priestley was the Swedish chemist, Scheele. He made a great many experiments on oxygen, and it

is quite an intellectual treat to read an account of Scheele's work— it is so full and complete, and the matter is reasoned out from the beginning. The only fault one has to find is that Scheele is as much interested in proving the truth of certain ideas of his own in regard to fire-air as in showing that the air contains this substance. We next come to the French chemist, Lavoisier, who was the first to combine all previous experiments, and to show that when a substance is burned it combines with one of the constituents of the air, gaining in weight thereby, and that it does not produce this supposed phlogiston. To that constituent Lavoisier gave the name which we now use, oxygen.

Then came Cavendish. He successfully recognised that the two chief constituents of the air could be made to combine with one another. He found that if electric sparks are passed through a mixture of oxygen and nitrogen, such a mixture as we have in atmospheric air, the two combine very slowly, and that the resulting compound can be absorbed by some alkali, such as caustic soda or potash. The nitrogen is gradually removed by this process, and it is necessary to add more oxygen than is normally present in air. To remove the whole of the added oxygen, after combination of all nitrogen, either one of the oxides of nitrogen was added, or phosphorus, both of which have the power of combining with the excess of oxygen, and so removing it. Cavendish made wonderfully accurate experiments by means of the very crude appliances of his day. He had an electrical machine turned alternately by himself and his assistant for more than a fortnight, and the sparks from this machine were passed through the mixture of gases, confined over mercury, along with a little potash. He was careful to explain, as the result of such experiments, that there was nothing else in air than nitrogen and oxygen, unless a very small residue, amounting toth of the whole, was something different. I may read you his words:"For this purpose I diminished a mixture of dephlogisticated and common air in the same manner as before, till it was reduced to a small part of its original bulk. I then, in order to decompound as much as I could of the phlogisticated air which remained in the tube, added some dephlogisticated air to it, and continued the spark until no further diminution took place. Having by these means condensed as much as I could of the phlogisticated air, I let up some solution of liver of sulphur to absorb the dephlogisticated air; after which only a small bubble of air emained