Sulphurous acid has of late years occupied a prominent place amongst disinfectants, since having been recommended by a committee of the German Empire for the cholera epidemic. Recently, however, its disinfecting power has been disputed. The Imperial Sanitary Board has therefore thought it necessary to submit this important matter to a renewed investigation. The necessary supply of sulphurous acid for disinfecting purposes is usually furnished by burning sulphur. This has, however, proved to be inefficient for several reasons. Sulphur is known not to burn very readily, and often to extinguish, and although this difficulty could be remedied by moistening it with spirit, the quantity of sulphurous acid evolved has been found to fall far short of the amount which might be produced with sufficient air supply. This is due partly to deficient ventilation, partly to a loss of gas by escape. Thus, in tightly-closed sulphurizing chambers, a larger amount of sulphurous acid than 6*5 volume per cent, cannot be obtained, and in a less perfectly closed space, as in rooms, only 40 per cent, of the available quantity of sulphur is converted into sulphurous gas.
Experiments have been made to obtain information about the communication of the gas to the different parts of a room, and also on the subject of disinfection, with a view to find out whether, and to what extent, the disinfectant penetrates into their interior. The method which was used for both purposes, and which has been made a special study by B. Proskauer, was the absorption or oxidation of the gas in a permanganate solution acidulated with hydrochloric acid, and subsequent gravimetric determination. The application of sodium bicarbonate and titration with iodine solution has proved in all those experiments totally useless. It has thus been found that the gas in the experimenting rooms generally diffuses uniformly in all directions. Yet in a few cases, there were differences between the ceiling and the floor observed up to 3 volumes per cent. Also, the mortar of the walls had unequally absorbed some sulphurous acid. Moreover, the spreading of the gas over the objects of disinfection, as well as the penetration into their interior, was very uneven.
Thin and very transmissible objects, such as letters, papers, clothes, permit the gas to enter copiously, but very little of it passes into the interior of voluminous and less permeable bodies, with a medium proportion of gas and the usual duration of the process. Thus, large commercial packages, as bales of goods and the like, cannot efficiently be sulphurized without loosening their covers and spreading out the contents. As this, however, cannot be practically carried out, sulphurous acid is not fit for the disinfection of packed goods. The same may be said with regard to dwellings and sick-rooms as well as ships. Sulphurous acid has hitherto been believed to possess the power of destroying germs of infection without in the least disintegrating the carriers of them. After the observations now made, this can no longer be admitted, as it has been proved that the moistening of the disinfecting objects, which seems necessary to bring about the effect, causes them, even in a less concentrated state of the sulphurous acid, to become injured, probably by assisting oxidation.
Also, experiments have been made upon various forms of fungi and other low organisms, and they have shown that sulphurous acid is capable of destroying them rapidly, if they have not yet assumed the state of permanency, and if they are lying near enough the surface to be sufficiently exposed to the gas. But to such organisms as have once passed into a permanent condition, the sulphurous gas, even in a high state of concentration, is utterly harmless, provided they are dry. It is true that by moistening them, all infectious matters become much more susceptible to the killing power of sulphurous gas. But the presence of water by no means affords absolute security, and it has been specially observed that spores arrived at the permanent state do not at all lose their capability of developing, if they are moistened and placed for 24 hours in a tightly-closed room which contains no less than 5 volumes per cent, of sulphuric acid. (G. Wolffhugel, Chem. Cent. Blatt.)