76 BIOLOGY AND TECHNIQUE 



bromine. Iodine with a much heavier atomic weight than either of the 

 former is distinctly less bactericidal. 



CHLORIDE OP LIME. Of the halogen compounds used in practice, 

 the most important is chloride of lime or bleaching powder. As to the 

 composition of this substance, there is some difference of opinion. It 

 was formerly believed to be a mixture of calcium hypochlorite, 

 Ca(C10 2 ), and of calcium chloride, CaCl 2 . The fact that the substance 

 is not deliquescent, however, speaks against the presence of calcium 

 chloride as such, and it is. probable that it consists of a single com- 

 pound with the formula CaOCL,. The action of acids or even of 

 atmospheric C0 2 upon this substance results in the liberation of 

 chlorine. For instance, 



Ca(Cl 2 O) + 2HC1 = CaCl 2 + 2HC1O. 

 2HC10 + 2HC1 = 2H 2 + 2C1 2 . 



Bleaching powder is readily soluble in about twenty parts of water. 

 According to Nissen, 1 solutions of 2 in 1,000 of this substance destroy 

 vegetative forms of bacteria in five to ten minutes. Its bactericidal 

 action depends on the hypochlorous acid formed. After water precipi- 

 tation an efficient dosage is 10 pounds to the million gallons. 



TERCHLORIDE OF IODINE (IC1 3 ) is an extremely strong disinfectant, 

 being efficient for vegetative forms in solutions of 0.1 per cent in one 

 minute and a 1 per cent solution destroying spores within a few 

 minutes. 2 



Painting with tincture of iodine (10 per cent) is a simple and 

 reliable method of sterilizing the skin. It is now used in many clinics 

 in sterilizing the field of operation. 



PEROXIDE OF HYDROGEN is formed by the action of dilute sulphuric 

 acid upon peroxide of barium. It readily gives up oxygen and acts 

 upon bacteria probably by virtue of the liberation of nascent oxygen. 

 In the presence of organic matter, such as blood, pus, etc., associated 

 with bacteria, H 2 O 2 is quickly reduced and weakened. It is important 

 that the H 2 2 come in immediate contact with the bacteria. In prac- 

 tice, therefore, blood and pus should be removed from wounds when 

 applying the H 2 Q 2 or a large excess of H 2 2 should be used. 



PERMANGANATE OF POTASSIUM, acting probably in the same way, is 

 a powerful germicide. It also is readily reduced by many organic sub- 

 stances often associated with bacteria, being rendered weaker thereby. 



1 Nissen, Zeit. f . Hyg., viii, 1890. 2 v. Behring, Zeit. f. Hyg., ix, 1891. 



