THE DESTRUCTION OF BACTERIA 109 



formaldehyd solution (commercial formalin) is poured over quick- 

 lime (CaO). The previous addition of concentrated sulphuric acid 

 to the formalin, in proportions of one to ten, increases the speed of 

 formalin liberation, and aids in limiting polymerization. One and 

 one-half to two pounds (one-half to one kilogram) of quick-lime 

 are used for every 500 c.c. of the formalin solution. The heat 

 generated in the slaking of the lime produces volatilization of the 

 formalin. 



A modification of this method is that of Schering 72 in which 

 tablets of paraform and unslaked lime are together laid into a pan 

 and warm water is poured over them. 



A very simple method is the potassium permanganate method of 

 Evans and Russell. 73 This method depends upon the active reaction 

 occurring when formalin and potassium permanganate are mixed. 

 Permanganate is placed into a bucket and the formalin poured over 

 it. The bucket should be large enough to prevent overflowing when 

 the mixture foams. Special galvanized iron pails are made with 

 funnel-shaped tops, and pails should be placed on a piece of iron 

 sheeting or bricks to prevent overheating of the floor; 500 c.c. of 

 commercial formalin and 250 grams of potassium per manganate 

 should be used for every 1,000 cu. ft. 



The room in which formaldehyd has been liberated is kept sealed, 

 in the manner already described, for at least twelve hours, after 

 which the windows and doors are opened. The odor which remains 

 after formaldehyd fumigation may be removed by sprinkling with 

 ammonia, or by the use of anyone of the various sorts of apparatus 

 devised for the liberation of ammonia. 



For the destruction of rodents, hydrocyanic acid gas is used in* 

 the fumigation of ships and houses. This is of especial importance 

 in controlling such diseases as plague. Recently Creel, Faget, and 

 Wrightson, of the United States Public Health Service, have studied 

 this method. They found hydrocyanic acid gas is more penetrating, 

 more toxic, and more easily applied than either sulphur dioxid or 

 carbon monoxid. 5 oz. of powdered potassium cyanid per 1,000 

 cu. ft. of space were sufficient to kill rodents. The gas is produced 

 by dropping the potassium cyanid into sulphuric acid of a specific 

 gravity of 1.84, or commercial grade 66B. The gas is as effective 



72 Schering, Hyg. Rundschau, 1900. 



n Evans and Russell, Rep. State Bd. Health, Maine, 1904. 



