“Michael Faraday.”
All of Faraday’s work in the liquefaction of gases, the discovery of new hydrocarbons, the study of the changes of steel through the slight admixture of other metals, the improvement of optical glass, and the long list of results which are to-day represented in millions of tons of products from thousands of factories, were obtained within these four walls. And nothing could better illustrate the earnestness and modesty of the great chemist than a little anecdote which Professor Dewar, standing in the centre of the room, calls to mind. “I never met Faraday,” says he, “but Tyndall told me this story of him. The first time Tyndall entered this laboratory, Faraday led him to this point and said: ‘Tyndall, this is a sacred spot. This is the spot on which Davy separated sodium and potassium.’”
The laboratory of to-day, however, looks very little like a scene of chemical industry. It has more the air of a machine shop, equipped with power and mechanical appliances of a very heavy kind. Instead of bottles and multi-colored liquids, all is metal and steam. The room is about thirty feet wide and fifty deep, the north front consisting entirely of glass windows opening on a well-lighted interior court. In the left-hand corner, at the back, is a large steam-engine, while a smaller one occupies the corner diagonally across. Shafts, wheels, and belting run to two large air-pumps and three steel compressors, each about the size and shape of a small travelling trunk, and used respectively for compressing oxygen, nitrous oxide, and ethylene. A fourth compressor, or double compressing chamber, is cylindrical in form, and is wrapped in thick white flannel. This is the source of the liquefied oxygen. The system which Professor Dewar has followed is not novel in its general principles, as he explains. Specifically, however, it contains many new inventions which he does not wish made public. They are mainly in the nature of stop-cocks and valves, which it took long study to invent, and which became perfect only after many failures and costly experiments. To liquefy oxygen, he simply used pressure at low temperatures; but as, up to 1878, both oxygen and nitrogen after repeated trials were looked upon as permanent gases, it may be imagined that the attainment of temperatures low enough was a problem which required an extraordinary command of mechanics as well as of chemistry to practically solve.
PROFESSOR DEWAR IN THE LABORATORY OF THE ROYAL INSTITUTION. FROM A PHOTOGRAPH TAKEN FOR M’CLURE’S MAGAZINE BY FRADELLE AND YOUNG, LONDON.
“The process of liquefying oxygen, briefly speaking,” says the professor, “is this. Into the outer chamber of that double compressor I introduce, through a pipe, liquid nitrous oxide gas, under a pressure of about 1,400 pounds to the square inch. I then allow it to evaporate rapidly, and thus obtain a temperature around the inner chamber of −90° C. (−130° F.). Into this cooled inner chamber I introduce liquid ethylene, which is a gas at ordinary temperatures, under a pressure of 1,800 pounds to the square inch. When the inner chamber is full of ethylene, its rapid evaporation under exhaustion reduces the temperature to −145° C. (−229° F.). Running through this inner chamber is a tube containing oxygen gas under a pressure of 750 pounds to the square inch. The ‘critical point’ of oxygen gas, that is, the point above which no amount of pressure will reduce it to a liquid, is −115° C., but this pressure, at the temperature of −145° C., is amply sufficient to cause it to liquefy rapidly. In drawing off the liquid under this pressure, I lose nine-tenths of it by evaporation, and I have not yet seen how to diminish that loss. Every pint of it which I collect therefore represents ten pints manufactured. In all, I have thus far collected and used about fifty gallons, and the cost of machinery and experiments, very generously met by subscription among members of the Royal Institution and others, has been about five thousand pounds sterling.” It should be here stated that one of the most generous contributors to the fund has been Professor Dewar himself, a large fraction of the sum having come out of his own pocket.
THE LECTURE-ROOM OF THE ROYAL INSTITUTION.
Going more into detail, he makes clear some of the mechanical and chemical difficulties which beset him in the work. “The secret of my success,” he continues, “has been the mechanical arrangements combined with the use of ethylene. This is a volatile hydrocarbon, and is the chief illuminating constituent of coal gas. The only means of keeping it liquid for any length of time is to surround it with solid carbonic acid. Faraday was the first to call attention to the properties of ethylene, and we manufacture it by heating sulphuric acid in a glass retort protected by an iron cover to 160° C. Alcohol heated to 160° C. is allowed to drip into it and ethylene results, passing off as a gas, which is stored, after being purified. It is then compressed by two pumps, the first with a six-inch plunger and six-inch stroke, and the second a two-inch plunger and six-inch stroke. This liquefies it under the pressure stated. It is nasty stuff to handle, as, whenever it becomes mixed, by leakage or otherwise, with nitrous oxide or air, an explosion is imminent, and we have had not a few explosions in the course of the work. It liquefies at −103° C. (−152.4° F.), and when boiled in a partial vacuum absorbs a large amount of latent heat. The failure of preceding attempts to liquefy oxygen is due to lack of knowledge of its ‘critical point,’ and the law which that phrase describes. As long ago as 1851, Natterer subjected oxygen to a pressure of 2,800 atmospheres, or over thirty tons to the square inch. He obtained no result, because, as I have said, no amount of pressure will affect it above −115° C. I liquefy it at −145° C. for two reasons. The lower the temperature at which it is liquefied, the less is the pressure required upon the oxygen and the greater is the amount of latent heat which it absorbs in evaporating. By evaporating, under exhaustion, oxygen liquefied at −145° C., I get as low as −200° C., which I could not do were it liquefied at a higher temperature.
