Chlorine has been most commonly used as chloride of lime (CaCl₂, Ca(ClO)₂). This is somewhat unstable in composition. A solution of sodium hypochlorite containing 10 per cent. of available chloride is preferable. Chloride of lime for sprinkling on decomposing matter should contain at least 10 to 15 per cent. of available chlorine. Sulphuretted hydrogen and other offensive gases are decomposed by it. Thus
SH₂ + Cl₂ = S + 2HCl. Its chief action is as an oxidising agent.
Thus H₂O + Cl₂ = 2HCl + O.
A large excess must be used in disinfecting, otherwise the chlorine may simply oxidise fœcal or other organic matter, and not effectually destroy contagia.
Methods of Use—(a) As a gas, by the action of hydrochloric acid on strong chloride of lime. The molecular density of chlorine is 35·5, of formic aldehyde 15, of sulphurous acid 32; and the rate of diffusion of gases being inversely to the square-root of their densities, clearly chlorine does not compare favourably as a gas with formic aldehyde. The bleaching effect of chlorine on coloured articles of apparel is a disadvantage.
(b) As a liquid: used thus chlorine is very efficient, applied either as a spray or brushed on walls and other surfaces. Delépine found that a solution of one part of chloride of lime in 100 parts of water applied to wall paper impregnated with tubercular matter, disinfected it in a few hours, or in a few minutes if the layer of infected matter was not thick.
Bromine, Iodine, and Euchlorine (a mixture of chlorine and Cl₂O₄) are efficient disinfectants.
Iodine Trichloride (ICl₃) was found by Behring to share with corrosive sublimate (HgCl₂) carbolic acid and cresol mixed with acids (see page [327]), the halogens (Cl, Br, and I), and chloride of lime a superiority over other disinfectants in their power of killing anthrax spores in a short time.
Permanganates have been largely used as disinfectants, but their value is small. Impure sodium manganate (Na₂MnO₄) with much common salt (NaCl) containing some permanganate is known as “Condy’s Green Fluid.” “Condy’s Red Fluid” consists of permanganate and sulphate of soda. To be of any use it must be employed in 5 per cent. solution. It stains fabrics brown, and it exhausts its feeble disinfecting power in first oxidising decomposing organic matter.
B. Deoxidising Agents.
Sulphurous Acid (SO₂) acts chiefly as a reducing agent on organic matter. It is used chiefly as a gaseous disinfectant, and for this purpose is generated (a) by burning 1 lb. of sulphur for every 1,000 cubic feet of space in the room (which will equal 1·12 per cent. of SO₂). The windows and chimney of the room are first closed; the sulphur is placed in a saucepan supported over a bucket of water, and its ignition is aided by a small quantity of methylated spirit. The door of the room is then sealed, and the room left until the next morning. (b) Carbon disulphide may be burned in a benzoline lamp. (c) SO₂ liquefied under pressure is supplied in cylinders available for convenient use. The experimental results of the action of SO₂ on various bacteria are somewhat discrepant. It probably is fairly efficient for some diseases, but not in tuberculosis.