FORMALDEHYDE 637 



combinations, from which silver chloride is only partially 

 precipitated. Silver salts are poisonous, though less so 

 than those of mercury. 



Iron and zinc salts have been credited with useful 

 disinfectant action ; but, in fact, their value is very small, 

 and no practical account need be taken of them. A very 

 strong antiseptic power has been attributed to copper 

 salts, which, according to some experiments, exercise a 

 sufficient disinfectant action on sporeless organisms, such 

 as the B. typhosus, to enable drinking water to be sterilised 

 from such infections by the small quantity of copper which 

 it dissolves (p. 599). 



There is some ground for connecting the disinfectant 

 action of metallic salts with a reducing action on some 

 forms of protoplasm, as pointed out by Loew. 



The permanganates have considerable germicidal power 

 when in strongly acid or alkaline solution, but the readiness 

 with which they are affected by organic substances makes 

 them unsuitable for practical use. Peroxides and ozone 

 are open to the same objection, and have less disinfectant 

 power. Hydrogen peroxide is used in the Budde process 

 for sterilising milk (p. 615), and ozone has been practically 

 applied in the sterilisation of water-supplies (p. 600). 



Organic substances. The methane and the aromatic 

 series furnish the disinfectants which are most important 

 in practice. 



Alcohol itself possesses some disinfectant power for 

 sporeless organisms, but only when absolute or in very 

 strong solution. 



Formaldehyde is by far the most important of the 

 methane group. It can be applied either as a solution 

 (formalin) or as gas. The gas can be produced by the 

 incomplete combustion or oxidation of methyl alcohol, 

 by the evaporation, with or without pressure, or spraying 

 of formalin, either alone or mixed with calcium chloride 



