Chloroform is mainly obtained commercially by the action of bleaching powder on alcohol or on acetone. Its technical preparation is described in Chemiker-Zeitung (1886, 10, 338), as follows.

The bleaching powder acts partly as an oxidising agent and partly as a chlorinating agent, first converting the alcohol, through various intermediate stages, into chloral, CCl3CHO. This is then decomposed by the calcium hydroxide of the bleaching powder into chloroform and calcium formate: -

On the large scale, experience has shown that good results are obtained by taking 4 parts of bleaching powder, 3 parts of alcohol (96 per cent.), and 13 parts of water, so that there are 16 parts of liquid to 4 parts of solid. The bleaching powder is preferably of strength 32.5 to 34.5 per cent. available chlorine: a lower strength is liable to diminish the yield through paucity of hypochlorite, whilst a higher develops too much heat.

In one form of plant, designed to give a daily output of 125 kilos. of chloroform, there are four generators, in which the reaction takes place. These are cylindrical iron vessels of diameter 2 metres and height 14 metres, fitted with stirrers, inlet tubes for steam and water, manhole for charging, and outlet to a condenser. A water tube outside the generator allows of the latter being cooled when necessary by flushing its surface with a little water. The charge for each generator is 300 kilos. of alcohol, 400 kilos. of bleaching powder, and 1.300 litres of water.

The alcohol is first placed in the generator, and then the charge of water (or the alcoholic wash-water and distillate from a previous operation). The stirrer is then set working, the bleaching powder added, the manhole closed, and the vessel heated by steam until the temperature of the liquid reaches 40°. The steam is then shut off, whilst the stirrer is allowed to work on until the temperature, which continues to rise, attains 45°. After stopping the stirrer the mixture slowly heats up further through chemical action to 60°; if the temperature rises above this the vessel is cooled.

The course of the reaction can be observed by means of a glass tube which is let into the connection between the generator and the condenser. A fine rain of chloroform, alcohol, and water is seen in the tube; this lasts a few minutes, and then the chloroform begins to pass over in quantity. When about 30 kilos. have dis-tilled, the stirrer is again set in motion until chloroform ceases to separate in the receiver, which is then changed.

The further distillate, consisting of alcohol saturated with chloroform, is collected separately. When a sample shaken with water gives no turbidity the whole of the chloroform is over, and the distillate is now collected apart until the runnings show a specific gravity of about 0 995. This last distillate consists of 500 to 600 litres of very dilute alcohol: it is used again in making up a fresh charge.

The chloroform thus obtained is purified from alcohol and ether by washing and rectification. The washing apparatus consists of a narrow vertical cylinder fitted with a screw agitator which gives a motion of the liquid from below upwards. Taps are placed in the side, to allow of the alcoholic washings being run off. After the chloroform has been well washed in this vessel, it is removed and rectified by distillation in a copper still. On an average, 988 kilos. of alcohol (96 per cent.) and 1,321 kilos. of bleaching powder are required to furnish 100 kilos. of chloroform.

Besson's process gives a good yield of a pure chloroform, and is a useful means of utilising waste chlorine in bleaching powder factories and electrolytic alkali works.

Chlorine is passed into strong alcohol until the density of the liquid reaches 35° Be. (sp. gr. 132). Two layers are formed, the heavier of which increases gradually until the chlorination is sufficient, when the liquid becomes homogeneous. A mixture of bleaching powder, milk of lime, and water, in the respective proportions of 5: 1: 20 parts for 1 part of alcohol (by weight) is then added, and the whole distilled. According to K. Ukita,1 the yield thus obtained is from 95 to 98 grams per 100 grams of alcohol.

On a large scale the process is made a continuous one, which is a great advantage. The alcohol is chlorinated in a vessel arranged somewhat on the principle of a small Coffey's still, and containing a number of perforated shallow trays placed one above the other. Entering at the top, the alcohol flows over these trays and meets a stream of dry chlorine, so that by the time it reaches the bottom the chlorination is effected. It then passes through a cooling worm into a vessel containing the bleaching powder, with which it is mixed. The mixture is next driven into a larger vessel heated by steam coils, where it is treated with the milk of lime at the proper temperature. The resulting chloroform vapours pass out and are rectified. By means of a screw worm, the mixture travels z 2 gradually from the entrance at one end of the larger vessel to the exit at the other end, and the feeding of the supplies is regulated so that the process can go on continuously. The yield of chloroform is said to be 95 to 105 parts per 100 parts of alcohol.1

1 J. Chem. Ind., Tokyo, 1918, 21, 210.

F. W. Frerichs2 gives a detailed description of experiments made with a view to improve the yield of chloroform obtained by the ordinary alcohol process. The method recommended is as follows: -

One hundred and twenty gallons of 94 per cent. alcohol are charged into a vertical still (6 ft. diameter, height 8 ft.) together with sufficient water to dilute the alcohol to 20 per cent. strength. In a vessel placed above the still, and provided with an agitator, a quantity of bleaching powder equivalent to 1,500 lb. at 35 per cent. strength is mixed with water, the amount of water used being sufficient to bring the diluted alcohol in the still down to 10 per cent. strength. After heating the alcohol to boiling by means of steam, the bleaching powder solution is introduced, in small quantities at a time, through a pipe reaching nearly to the bottom of the still. The whole charge fills the still to less than three-fourths of its total capacity.

The reaction sets in at once. The chloroform is distilled off and collected, the layer of aqueous alcohol obtained in the receiver being run off into a large vessel for use in the next charge. The average yield obtained over an extensive period corresponded with 100 lb. of chloroform from 11.22 gallons of 94 per cent. alcohol and 977 lb. of 35 per cent. bleaching powder, the consumption of steam being 2 tons at a pressure of 80 lb.

Chloroform is very largely made from acetone and bleaching powder, the process being very similar to the alcohol method.3 Whether acetone or alcohol is used depends upon the relative costs of the two in comparison with the yields obtained. Acetone gives the better yield, and a few years ago had largely supplanted alcohol as a raw material for chloroform; but the position afterwards became reversed, on account of scarcity of acetone.

In this country a certain amount of chloroform is made from duty-paid ' rectified ' spirit; most, however, is produced from industrial methylated spirit, or from acetone, as the case may be. In particular circumstances, specially denatured duty-free spirit has been employed, the denaturants being, for example, bleaching powder and methyl alcohol. If sufficiently purified, the products obtained are almost indistinguishable one from another. Chloroform prepared from alcohol, however, is liable to contain a minute quantity of ethyl chloride,1 and that from methylated spirit traces of methyl compounds.

1 D.R.-P., 129237. 2 J. Ind. Eng. Chem., 1912, 4, 345, 406.

3 Sadtler, Pharm. J., 1889, [iii], 20, 84.

When intended for use as an anaesthetic, the chloroform is further purified by washing with water, then with dilute sulphuric acid, and afterwards with dilute sodium hydroxide solution or lime-water, and once again with water only. Finally it is dried with fused calcium chloride and re-distilled.

Pure chloroform boils at 61°, and has a specific gravity of 150 at 15.5°. It is prone, however, to decompose slightly under the action of air and light, and a small quantity of alcohol is usually added as a preservative. This affects both the specific gravity and the boiling point. The British Pharmacopoeia requires 2 per cent. of absolute alcohol to be added, and gives the specific gravity of the official chloroform as 1483 to 1487, with a boiling point not below 60°. From 1/2 to 1 per cent. is often added to non-official chloroform, bringing the sp. gr. to about 1495-1.490.