92 BIOLOGY AND TECHNIQUE 



room. Modifications of this metliod are in common use, some well- 

 known firms preparing so-called "paraform candles," in which para- 

 form, in the powdered state, is volatilized by heat. 



A simple method of generating formaldehyde is that which is known 

 as the "lime method." In a wide shallow pan 40 per cent formalde- 

 hyde solution (commercial formalin) is poured over quicklime (CaO). 

 According to Park, the previous addition of concentrated sulphuric 

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

 speed of formalin hberation, and aids in limiting polymerization. 

 About one and one-half to two pounds (one-half to one kilogram) of 

 quicklime 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 ^ in which tablets 

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

 water is poured over them. 



A highly efficient method, which has universal approval because of 

 its simplicity, is the potassium permanganate method of Evans and 

 Russell.^ This method depends upon the active reaction occurring when 

 formalin and potassium permanganate are mixed. In practice, about 

 300 grams of small crystals of potassium permanganate are poured into 

 a half liter of 40 per cent formalin. The mixture results in an active 

 evolution of heat and the evaporation of formahn together with water 

 vapor. Because of the active foaming which takes place, high cylin- 

 drical vessels should be used, about one foot in height, preferably with a 

 funnel-like flare at the top. The yield of gas by this method is said 

 to be about 80 per cent of the amount present in the solution, and 

 within the first five minutes most of this is liberated. 



Harrington ' states that the equivalent of 110 c.c. for formalin 

 suffices to produce sterility within two and a half hours in a space of 

 one thousand cubic feet. 



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

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

 the windows and doors are opened and thorough airing practised. The 

 odor which remains after formaldehyde fumigation may be removed by 

 sprinkling with ammonia, or by the use of some one or another of the 

 various sorts of apparatus devised for the liberation of ammonia. 



' Schering, Hyg. Rundschau, 1900. 



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



'Harrington, "Practical Hygiene," Phila., 1905. 



