AN EFFICIENT DISINFECTANT 761 



usually have some organic coating, it should be stable in 

 the presence of organic matter ; and as this coating 

 is often of a greasy character, it should, especially if 

 intended for use on dirty or greasy surfaces, have high 

 solvent power for grease. For use when heat can also 

 be applied, whereby its activity is enhanced, unless it 

 breaks up, it should be stable at all reasonable tempera- 

 tures. These conditions may be considered to be indis- 

 pensable. It is further desirable that it should have a 

 sufficiently high specific efficiency to allow of its being 

 used in a readily diffusible dilution ; that its efficient 

 solution or emulsion should be relatively cheap, not act on 

 metals, nor be destructive to or stain fabrics, and be 

 neither caustic nor toxic. Some disinfectant substances 

 may now be considered more in detail. 



Acids. All acids have disinfectant action, and their 

 relative values are interesting in the respect that for them 

 a general law has been fairly welt established by Von 

 Lingelsheim, and confirmed by Boer namely, that the 

 efficiency varies with the degree of acidity. Solutions of 

 acids not of equal percentage concentration, but of equal 

 acidity, have approximately the same disinfectant 

 efficiency whatever may be the acid, and whether it be 

 inorganic or organic. 



The acids have no great practical application in dis- 

 infection. That which has been most commonly used is 

 sulphurous acid, applied either direct from burning of 

 sulphur (in which case it will also contain S0 3 if there is 

 sufficient moisture to hold the sulphur dioxide in solution) 

 or by the use of the liquefied gas. It produces a slow 

 superficial disinfection of a weak and uncertain character 

 even under laboratory conditions. Such experiments 

 avoid, however, to a far greater extent than is possible in 

 practice the difficulty of diffusion, and the unequal 

 diffusion of sulphurous acid in air and its small power of 



