This section is from the book "Welding And Cutting Metals By Aid Of Gases Or Electricity", by L. A. Groth. Also available from Amazon: Welding and cutting metals by aid of gases or electricity.
It has been known for ages that matter is capable of existing . in three different physical states: the solid state, the liquid state, and the gaseous state.
It has also been long known that most solids can be transformed into liquids by the application of heat, and that many liquids, water for example, can be transformed into vapour by a further addition of heat. Conversely, it is known that certain aeriform substances, such as steam, are converted into liquids by the mere abstraction of heat.
It was believed that an essential difference existed between gases and vapours, vapours being condensible to the fluid form, while gases were believed to be perfectly aeriform, and not condensible by any experimental means at our disposal.
In the early part of the nineteenth century the validity of this distinction came to be doubted, and Faraday, at the suggestion of Davy, undertook the systematic study of the question, with the result that he succeeded in reducing to liquid form quite a number of gases that had previously resisted liquefaction. Shortly afterwards Thilorier, Cagniard de la Tour, Regnault, Natterer, and many others improved the methods. Nevertheless oxygen, nitrogen, and hydrogen, or the "permanent gases," still resisted all attempts, until Andrews in 1863 made the important pronouncement that a certain temperature exists above which the gases cannot be liquefied by any pressure whatever, this temperature now being known as the "critical temperature,"1 and similarly the "critical pressure," or the tension that exists in a liquefied gas at the critical temperature, and the "critical volume," or the volume occupied by a unit mass of gas at its critical point. The problem of liquefying the permanent gases, and any other gas, was therefore resolved into the production of exceedingly low temperatures.
1 For Andrews' conception "critical temperature " it would be better to substitute the conception " critical density," or the least density which the substance can have as a liquid.- Wroblewski.
This is a mixture of, approximately, 21 per cent. of oxygen, 78 per cent. of nitrogen by volume, and 1 per cent. of carbon dioxide and variable quantities of water vapour, ammonia, and other bodies, according to locality and conditions.
Owing to the complex composition of air, several different products are obtained by its liquefaction, notably liquid oxygen and nitrogen and solid carbon dioxide.
The principal method of effecting the liquefaction of atmospheric air on a commercial scale, after Perkins, in 1823, erroneously believed that he had liquefied air, and numerous unsatisfactory attempts by others, was proposed by the late Sir William Siemens in 1857, followed by the simultaneous but entirely independent labours of Louis Cailletet and Raoul Pictet, who succeeded in liquefying atmospheric air on a small laboratory scale, the former on the 30th December, 1877, and the latter on the 10th January, 1878, both having employed quite different means.
The impetus and foundation stone to the important industry to be created were, however, laid by Sir James Dewar, who in 1885 succeeded in producing liquid air from the atmosphere, an achievement which aroused great anticipations as giving the nucleus to the solution of problems of unforeseen importance to almost every branch of industry.
Amongst the numerous and different methods that were suggested from time to time, those of Carl Linde (1895) Conrad Mix and Heylandt (1896), Hans Knudsen (1899), and Eugene Claude (1900), with modifications of the methods for separation of gases by Rene Levy and Andre Helhronner (1902) and Raoul Pietet (1903), have brought the liquefaction of atmospheric air to an accomplished fact.
As to the commercial application of liquid air, it may be looked upon as an important, if not the principal, source of nitrogen and oxygen.