Inorganic Disinfectants 213 



process of germicidal action many and varied activities are 

 at work, and, as all are not understood, the subject is a 

 difficult one to handle in a limited amount of space. With 

 the salts, acids, and bases it appears from the researches of 

 Kronig and Paul* that ionization in solution plays an import- 

 ant part in the destruction of micro-organisms. They found 

 that double metallic salts, in which the metal is a constituent 

 of a complex ion in which the concentration of the dissociated 

 metal ions is consequently very low, have very little germicidal 

 power, but that simple salts, in which the condition is reversed, 

 have correspondingly higher germicidal power. Dissocia- 

 tion, therefore, seems to have much to do with the matter. 



Inorganic Disinfectants. 



ACIDS. These agents are seldom employed, since the concentration 



required makes them objectionable. 



ALKALIS. The same holds good with regard to these agents. 

 SALTS. In this group we find some of the most powerful and most 



useful germicidal substances. 



Copper Sulfate. It is curious and interesting that while this 

 salt is highly destructive to algae and other low forms of 

 vegetable life, it is not of much value for the destruction of 

 bacteria. Its chief use is for the destruction of the green algae 

 that sometimes render the water of reservoirs dirty and offen- 

 sive. Some of the salt contained in a gunny-sack and per- 

 mitted to drag to and fro over the surface of the water behind 

 a slowly rowed boat usually accomplishes the end, the actual 

 quantity dissolving in the water being almost infinitesimal. 

 Mercuric Chlorid (HgCl 2 ). This is probably the most generally 



useful as well as one of the strongest germicides. 



A study of its activity under varying conditions is instructive as ex- 

 emplifying the varying behavior of germicides under the varying con- 

 ditions under which they may be employed. 



First, it makes great difference whether the mercuric chlorid is added 

 to the substratum containing the bacteria, or whether the bacteria are 

 added to solutions of the germicide. 



Thus, when the salt is dissolved in gelatin in a concentration of 

 i: i,ooo..ooo, anthrax bacilli cannot grow. If it is dissolved in blood- 

 serum, the concentration must be increased to i : 10,000 to prevent their 

 growth. 



When the anthrax spores are dropped in solutions of the salt, Kronig 

 and Paul found that they were killed in twelve to fourteen minutes by 

 i : 65 solutions; in eighty minutes by i : 500 solutions, and in two hours 

 by i : looo solutions. When the reaction takes place in albuminous 

 media Behring and Nochtf found that much more time was required. 

 Thus, the destruction of the spores by a i : 100 solution required eighty 

 minutes, and a i : 1000 solution twenty-four hours to completely kill all 

 of the spores. 



LaplaceJ and Panfili found that the addition of 5 per cent, of tar- 

 taric or hydrochloric acid facilitated the germicidal action through the 



* "Zeitschrift fur Hygiene," 1897, xxv, i. t Ibid., ix, 432. 



J "Deutsche med. Wochenschrift," 1887, 866; 1888, 121. 

 "Ann. Ig. Roma," 1893, m, 527. 



