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From which it may be concluded that at ordinary temperatures commercial cresol disinfected the bacterium termo in somewhat less dosage than phenol, 10 per cent. cresol being equal to 50 per cent. phenol; at higher temperatures the action was equal.

(265) Experiments on the Disinfectant Action of Phenol
and the Cresols on Sewage.

The phenol was absolute crystalline phenol, the cresols were obtained from Kählbaum; 1 per cent. solutions were used, but the volumes added to the sewage were proportional to the molecular weights of phenol and cresol. Equal quantities of sewage were placed in test tubes; to some of the tubes 47 c.c. of the 1 per cent. solution of phenol were added, into others 54 c.c. of the cresols; these reacted for twenty-four hours, the disinfected solutions were then made up by the aid of sterilized water, with suitable precautions, to a definite bulk of which weighed drops were taken and cultivated in the manner detailed at p. 315. It may be necessary to observe that the quantities of disinfectants being mutually equivalent, the relation of the weights was 36 cresol to 30 phenol, On the eleventh day the colonies were counted:

Ortho-cresol l'henol

Mean number of colonies
per 100 mgms, sewage.

99 136

Meta-cresol
Para-cresol

Mean number of colonies
per 100 mgms, sewage.
146
170

From which it may be deduced that ortho-cresol is a little superior to phenol and the other cresols, and that the disinfecting action of phenol and meta-cresol is pretty well equal.1 Experiments were also made as to the relative power of these substances to destroy the odour of highly offensive sewage. The sewage was diluted, and a sufficient quantity of the disinfectant added so that the strength was equal to 5 per cent. The mixture was allowed to stand for about an hour. The disinfected sewage was then slightly warmed, sucked up and down a wide tube, and the lower end of the tube being still in the flask just above the liquid, the nostril was applied to the upper end of the tube, and the vapour sniffed up. The results were:

Phenol . . . A very faint urinous odour. | Meta-cresol . Feeble aromatic odour.
Ortho-cresol . Aromatic odour.
Para-cresol
Decided urinous odour.

1 On the other hand, Carnelley and Frew find that with regard to the diderivatives of benzene, the para-compounds are more antiseptic than the ortho- and meta-compounds. Journ. Chem. Soc., 1890. Chemical News, June 13, 1890.

There is no doubt of the superiority of ortho-cresol over any of the others; the more especially when it is considered that the odour is unmistakably agreeable. Unfortunately ortho-cresol is at present only a scientific curiosity and of a high price. In practice there is no real difference in the action between pure phenol and the so-called carbolic acid of commerce, provided equal strengths be compared; the crude dark coloured 90 per cent. carbolic acid used extensively by local bodies mostly contains large quantities of cresol, and only small quantities of phenol, the manufacturer having as far as possible separated all crystalline materials, but as it has been shown that cresol is a little superior to phenol, and the price is very much less, it is folly to use the dearer article for disinfecting purposes on a large scale.

(266) Koch's Experiments on Phenol.

Koch has made many experiments on the effect of phenol on anthrax. He found that a couple of minutes steeping of threads contaminated by spore-free anthrax in a 1 per cent. aqueous solution of phenol, was sufficient to destroy the bacilli; on the other hand spore anthrax was not killed save by prolonged contact with much stronger solutions; e.g., an aqueous 3 per cent. solution acting for five days failed to disinfect; 4 per cent. succeeded in destroying the spores after three days, and 5 per cent. after two days. He found that carbolic acid dissolved in oil or strong alcohol had no disinfecting power, and that of the phenol salts, a 5 per cent. solution of sulfo-carbolate of zinc was capable of destroying anthrax spores if the latter were soaked in the solution for five days, but sodium-phenol as well as sodium sulfo-carbolate had little effect.

(267) Schill and Fischer on the Action of Phenol on

Tuberculous Matters.

Schill and Fischer in their elaborate investigation on the disinfection of tuberculous matters, by various disinfectants, found that fresh sputa still produced tuberculosis when injected into animals after being treated for twenty hours with solutions of phenol from 1 up to 3 per cent., a 5 per cent. solution acting for two hours failed to disinfect, but acting for twenty-four hours was invariably successful. On the other hand, if an

antiseptic action only is desired, there are plenty of observations to show that traces of phenol inhibit the growth of a large number of micro-organisms.

(268) Summary of the Action of Phenol and Cresols as Disinfectants.

Phenol and the cresols hold a high position as disinfectants: a 1 per cent. solution is strong enough to destroy the more feeble infections, but to be certain that the more resistant forms of germ life are annihilated it will be necessary to use at least 5 per cent. solutions in water, and the action must be prolonged; if specific excreta are treated it is doubtful whether 5 per cent. solutions are of sufficient strength, because associated with the hurtful material there is a quantity of organic matter which must on the one hand remove some of the phenol from the sphere of action, and on the other impede the contact of the phenol with the substances which we wish to disinfect.

(269) Creasote.

Wood tar creasote is a mixture of several phenol-like bodies, the chief of which are guiacal, or oxycresol, C,HO2, boiling point 200°210°, and creasol, C,H12O2, boiling point 217°.

2

The considerable insolubility in water of creasote is a bar to its extensive use as a disinfectant. It is otherwise probably about equal to cresol, but few experiments of an exact kind, made in the modern way have been hitherto published, besides which, the uncertain composition of commercial creasotes renders any but a general statement impossible. Its powerful antiseptic properties, as for instance in the preservation of timber, are well known.

(270) Phenyl-propionic and Phenyl-acetic Acids.

Phenyl-propionic and Phenyl-acetic acids have been investigated by Klein (Thirteenth Annual Report to the Local Government Board, Supplement). He found that as regards spore-free bacillus anthracis, the bacilli were certainly killed on exposure, even for a few minutes, to solutions of either of the acids in the strength of 1:400 or less; with regard to greater dilutions a longer time was necessary, and phenyl-acetic proved to be a little weaker than phenyl-propionic. These aromatic acids were also efficacious in destroying the virus of swine plague, when the strength was not

less than 1800, but experiments on tubercle bacillus, even with strong solutions, produced no very appreciable effect.

Mr. G. F. Dowdeswell (op. cit. p. 193), while recognising both these acids as powerfully antiseptic, did not find in experiments on symptomatic charbon that they had any constant or determinate action on the virus.

(271) Sulphur Dioxide (Sulphurous Acid Gas), SO2

This gas is formed whenever sulphur is burnt in air or oxygen. Its molecular weight is 64, vol. weight 32, sp. gr. 2,217. Its composition by weight is equal parts of sulphur and oxygen; its composition by volume is 1 volume of sulphur, and 2 volumes of oxygen condensed into two.

Sulphurous acid, or more accurately sulphur dioxide, is in its concentrated form an irrespirable gas, and even when dilute causes considerable laryngeal irritation; it bleaches many organic colours, and reddens litmus.

It is injurious to vegetation, and when present in the atmosphere in but minute quantity some plants are affected by it.

It is the most common acid in the air of towns, being derived from the burning of sulphur contained in the coal.

Sulphur dioxide may be condensed to a liquid by the application of cold or pressure, or both combined. The pure liquid anhydride is a thin blue liquid of sp. gr. 1-491, and is an article of commerce, and may be bought in quantity, but the liquefied anhydride may be dangerous if trusted to unskilled hands.

Sulphur dioxide has been for a long time the most common and favourite disinfecting agent, by reason of its cheapness, and the ease with which it can be generated. The usual way has been to take about a pound of roll sulphur, seal up a room as hermetically as possible, light the sulphur in some proper receptacle, and let it burn as long as it will. Or, a still more convenient method is to take an ordinary benzoline lamp, charge it with carbon bisulphide and light; as the carbon bisulphide is consumed the sulphur is emanated as sulphur dioxide.1 Seabury's sulphur candles are also

Ckiand Bey's lamp is used in some of the continental hospitals for the purpose of burning safely CS. It is very ingenious, and is so arranged that as the volatile liquid sulphide burns away water takes its place; finally, when all is burned, the water rises to a level with the wick. It is described and figured in Dujardin Dumetz's L'Hygiene Prophylactique. Paris, 1889.

A A

convenient; they consist of a cake of sulphur, in the centre of which are two or three wicks, saturated with nitre; the wicks light easily, and the whole cake burns gradually away.

It is however doubtful whether sulphur dioxide will retain its place as a disinfectant; for although there are remarkable discrepancies as to the results obtained by different experimenters, the impression remains that it is an uncertain agent.

When sulphur is burnt in a perfectly close space, its consumption is limited by the quantity of air in that space: theoretically a cubic foot of air will burn up 624 grains of sulphur, but it will not do this unless copiously supplied with air.

The best results are obtained in imperfectly ventilated places by well moistening the sulphur with methylated spirit; under the best conditions the air of the room thus disinfected may contain 10 per cent of SO,.

(272) Wolffhugel's Researches on the Disinfecting Properties of Sulphurous Acid Gas.

Gustav Wolffhugel1 has made the most elaborate research on the value of sulphur dioxide as a disinfectant. The following is a brief abstract of his research. With the addition of alcohol under strict experimental conditions, 40 per cent. of the possible total quantity of sulphur in a closed space can be burnt, and in rooms the volume percentage may reach 10 per cent. To attain the maximum amount the sulphur must be broken up into pieces not larger than a hazel nut, and divided about a room, never putting more than a pound in one vessel.

Experiments were made on loss of SO, during the process of disinfection in rooms, this was found to range from 38 to over 90 per cent of the gas developed. The causes of loss being leakage, oxidation to sulphuric acid, precipitation with water, and absorption by porous substances (this latter can of course hardly be called waste in a disinfecting point of view). In some of the experiments the walls were moistened with water, but the results obtained were not encouraging, the volume of free SO, in the air being notably diminished. The diffusion of SO2 evolved in a room was found to be fairly equal, samples of air taken from different

1 Mittheilungen aus dem Kaiserlichen Gesundheitsamte.

Bd. i. 1881.

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