In the introductory chapter it was pointed out that Hennell, as long ago as 1828, had effected a synthesis of alcohol from ethylene. This gas was dissolved in sulphuric acid, forming ethyl hydrogen sulphate, from which alcohol was obtained by diluting the acid solution and distilling it.

This method of obtaining alcohol has remained a purely laboratory operation for the greater part of a century. Indeed, instead of ethylene being used as a source of alcohol, the latter substance has been the most convenient material from which to obtain ethylene. With the coming of the electric furnace, however, matters have altered. By its aid calcium carbide is produced, and serves as a cheap source of acetylene. Hence it has become practicable, by converting acetylene into ethylene, to utilise Hennell's synthesis, and thus obtain alcohol on a commercial scale from acetylene or from calcium carbide. The ultimate raw materials of the carbide, of course, are coal and chalk.

The waste gas from coke ovens contains from 1 to 4 per cent, of ethylene. If a practicable means of. utilising this by the sulphuric acid process were found, coke oven gas might prove to be an economical source of alcohol.

A drawback to this method appears to be the relatively considerable volume of strong sulphuric acid that would be necessary for operations on a large scale. Another possibility, however, is the conversion of acetylene into acetaldehyde, and the reduction of the latter to alcohol.

Various patents have been taken out for methods of obtaining ethylene and aldehyde from acetylene.

Thus Traube1 converts acetylene into ethylene by the aid of chromous salts in acid solution, under pressure. The chromous salt can be regenerated from the resulting chromic compound by reduction with zinc, or by electrolytic methods. For example, 4 parts of crystallised chromium chloride, 20 parts of hydrochloric acid (25 per cent. strength), and 4 parts of zinc are shaken with 0 4 part by weight of acetylene under pressure. Ethylene and hydrogen are produced, and can be separated by ordinary methods.

In a process described by Freeman,2 ethylene is said to be produced by injecting a current of hydrogen into an electric arc between carbons in a chamber from which air is excluded. The ethylene thus obtained is led through a tower, where it is absorbed by sulphuric acid. The alcohol is distilled off, and purified by rectification.

1 D.R.P., 287565, 1913; 295976, 1914. 2 B. P. 20893, 1913.

In another process,1 ozonised oxygen (540 litres) is made to act upon a mixture of acetylene (45.6 litres) and hydrogen (173 litres) at a low temperature. The product other than the escaping gas (oxygen) is neutralised with sodium carbonate and fractionally distilled; it gives first aldehyde and then alcohol. The yield of alcohol is said to be about one-fourth of the theoretical.

Hibbert and Morton2 obtain aldehyde (a) by passing acetylene into dilute sulphuric acid containing a salt of mercury and a salt of a relatively weak acid, such as a borate, which is not reduced under the working conditions; or (6), by passing acetylene into a solution containing a salt of mercury and an acid salt of a strong acid, e.g., a bisulphate, but practically no hydrogen ions. A salt of a weak acid may also be present in process (b). The acetalde-hyde produced is distilled off simultaneously.

Dreyfus3 obtains aldehyde by the combination of water with acetylene in the presence of a mercury salt. The nitrate, the acetate, and the chloride are the most active. A liquid medium is employed in which the mercury compound is soluble, such as, for example, acetic acid; so that the catalyst acts in a nearly homogeneous system. Or acetone may be used as medium; it has a greater solvent action on acetylene than water has. The acetic acid is employed at a concentration of 80 per cent., and this is maintained by adding water as required to replace that taken up by the acetylene. From 8 to 10 per cent. of the catalyst is used in the mixture. In Dreyfus's process, the aldehyde produced may, if required, be oxidised forthwith to acetic acid by including an oxidising agent in the mixture; the oxidiser may be a peroxide, or oxygen, with a catalyser such as cerium oxide or manganese acetate. The temperature is kept between 50° and 100°.

Dilute sulphuric acid (15 to 30 per cent)., with mercuric oxide as catalyst, has also been used to effect the hydration of the acetylene.

A German process,4 based on a similar principle to that of Dreyfus's method, is thus described: - Acetylene is led into a well-stirred mixture of glacial acetic acid (1000 grams), strong sulphuric acid (22.5 grams), and mercuric oxide (100 grams), at a temperature of 80-85°. The excess of gas passing out is conducted successively through a fractionating apparatus, a condenser cooled by a freezing mixture, an absorption vessel charged with water in which the aldehyde is absorbed, and then back to the reaction-vessel again. Absorption takes place at the rate of 100 to 200 litres per hour, and water is added to replace that used up (C2H1 + H1O = CH3CHO).

1 D.R.-P., 149893, 1902, Jay & Co.

2 U.S. P., (a) 1213486, (6) 1213487, 1917.

3 F.P., 479656, 1914.

4 B.P., 5132, 1915, Consortium f. Elektroch., Nurnberg.

Aldehyde produced in this and other processes may then be either reduced to alcohol or oxidised to acetic acid, according to circumstances.

The reduction is effected by passing a mixture of aldehyde vapour and pure hydrogen in excess over a column of reduced nickel at a temperature of 140°.1 At a higher temperature (180°), the aldehyde is decomposed into methane and carbon monoxide; and in any case the reaction tends to be reversed by the dehydrogenation of the alcohol formed. At 140°, however, about 80 per cent. of the aldehyde passing once over the nickel is converted into alcohol. The catalyst is prepared by reducing nickel oxide with hydrogen at a temperature not higher than 350°. On a large scale, the main process is carried out in metal tubes, preferably of nickel heated electrically, in order to regulate the temperature most easily.

The outgoing vapours are strongly cooled in order to condense the alcohol and unchanged aldehyde, which are then separated by fractional distillation.

In order to avoid "poisoning" the catalyst, it is necessary to use well-purified hydrogen and aldehyde.

According to the claim of A. G. Bloxam (for the Electrizitatswerk Lonza),2 a large excess of hydrogen is advisable, in order to reduce the proportion of unchanged aldehyde in the product, and also to keep the reaction-chamber at the proper temperature by conducting away the excess of heat developed in the reaction, which is a strongly exothermic one (nearly 300 Cal. per kilo. of alcohol produced).

With a six-fold excess of hydrogen above the theoretical, the alcohol obtained is free from malodorous by-products, and contains but little aldehyde. If the hydrogen and aldehyde-vapour are passed at a temperature of 90° into the reaction-chamber containing the nickel, a thirty-fold excess of hydrogen keeps the temperature of the chamber at 150°. The excess of hydrogen can be returned again to the chamber through an external circulation system.

The foregoing process, or some modification of it, is understood to be actually in use in Germany (1918) for producing both alcohol and acetic acid.

1 Sabatier and Senderens, Compt. rend., 1903, 1,37, 301, 2 B.P. 120163, 1918.

It was reported in 1917 that the leading Swiss hydro-electric company, working with the Lonza aluminium company, had completed researches upon the production of alcohol from calcium carbide, and that the Swiss Federal Government jointly with the Lonza firm would introduce the new industry into Switzerland. Presumably the process is based upon either the ethylene or the aldehyde synthesis, but the actual details do not appear to have been published. It was computed that an output of 7,500 to 10,000 metric tons would be reached, leaving a surplus for export above the country's requirements. In 1918, a large plant, capable of producing 28 millions of gallons per annum, was stated to be in course of erection at Visp.

In Germany, it may be mentioned, the production of alcohol from cellulose and from calcium carbide is to be reserved to the State (Imperial Spirit Monopoly Bill, 1918). This is done in the interests of the farming community, "in order to guard against a development which, under a system of free competition, would be dangerous to agriculture." The manufacture of alcohol from calcium carbide is said to have been carried out very successfully for some time past, especially by the Hochst Farbwerken.