THE DESTRUCTION OF BACTERIA 75 



known that metallic salts are ionized in these substances to a much 

 slighter degree than they are in water. 1 



On the other hand, the addition of moderate quantities of ethyl 

 and methyl alcohol or acetones to aqueous solutions of silver nitrate or 

 mercuric chloride, definitely increases the disinfecting action of such 

 solutions. In the case of mercuric chloride, Kronig and Paul obtained 

 the most powerful effects in solutions to which alcohol had been added 

 in a concentration of 25 per cent. For this empirical fact a satisfactory 

 explanation has not yet been found. Kronig and Paul suggest that low 

 percentages of alcohol may facilitate the penetration of the disinfectant 

 through the cell membrane and thus increase its efficiency, while high 

 percentages of alcohol have the opposite effect, by decreasing the degree 

 of dissociation. In this connection it has been suggested, however, 

 that absolute and strong alcohols possibly act as desiccating agents, 

 thus actually rendering the bacteria dry and less susceptible to dele- 

 terious chemical influences. 



In the case of acids and bases the same authors have determined 

 that the powers of disinfection of these substances are again directly 

 proportionate to the degree of their dissociation: that is, to the concen- 

 tration of the hydrogen or hydroxyl ions, respectively. The hydrogen 

 ions are more powerfully active than the hydroxyl ions in equal con- 

 centration; acids, therefore, are more efficient disinfectants than bases. 



A fact which appears to strengthen the opinion as to the relationship 

 between bactericidal powers and dissociation, is that brought forward 

 by Scheuerlen and Spiro, that the addition of NaCl to bichloride of 

 mercury solutions reduces the disinfecting power of such solutions, in- 

 asmuch as it diminishes the concentration of free ions. In practice, 

 however, NaCl or NH 4 C1 is added to bichloride of mercury solutions, 

 since these substances aid in holding in solution mercury compounds 

 formed in the presence of alkaline albuminous material, blood serum, 

 pus, etc. 



In regard to the halogens, Kronig and Paul have shown that the 

 germicidal power of this class of elements is inversely proportionate to 

 their atomic weights. Thus, chlorine with the lowest atomic weight is the 

 strongest disinfectant of the group. Next, and almost equal to this, is 



1 Water is the strongest dissociant known. Methyl alcohol has about one-half to 

 two-thirds the dissociating power of water (Zelinsky, Zeit. f. physiol. Chemie, xx, 

 1896). Ethyl alcohol allows dissociation much less than methyl alcohol; ammonia 

 allows dissociation to about one-third to one-fourth the extent of water. See Jones, 

 "Elements of Physical Chemistry," p. 371, Macniillan, New York, 1902. 



