STERILIZATON — ANTISEPSIS--FOOD PRESERVATION 77 



may be mentioned creolin, cresol and lysol. They are all slightly 

 superior to carbolic acid in actual germicidal value. 



Formalin is a 40 per cent aqueous solution of formaldehyde, 

 H2CO. Numerous investigations have shown it to possess, both 

 in the liquid and gaseous forms, remarkable disinfecting power 

 under certain conditions. In solutions of i-iooo an exposure of 

 twenty-four hours is necessary to destroy the staphylococcus 

 pyogenes aureus, while 1-5000 is sufficient to restrain its growth 

 (Slater and Rideal). Its use in a gaseous form as a house 

 disinfectant is by far the most important application at the present 

 time. 



From 250 to 500 c.c. of formalin together with 500 to 1000 c.c. 

 of water should be vaporized for each 1000 cubic feet of air space 

 in the room, and the room should remain tightly closed for at 

 least four hours, preferably over night. Many methods of 

 vaporizing formaldehyde have been devised. Some form of 

 tank, provided with heating apparatus and with an outlet tube 

 which passes through the keyhole into the room, is perhaps the 

 most convenient, where much disinfection has to be done. If 

 apparatus of this sort is not at hand, good results may be obtained 

 by putting the formalin and the water previously heated to boil- 

 ing, in a large pail in the center of the room, and then adding 

 rapidly crystalline potassium permanganate, about 200 grams to 

 each 500 c.c. of formalin used. The permanganate oxidizes 

 some of the formaldehyde and produces heat to evaporate the 

 rest of it. From 25 to 50 per cent more formalin should therefore 

 be used for a given air space. It is well also to add about 10 per 

 cent of glycerin to the water so as to raise the boiling-point some- 

 what and insure more complete vaporization of the formaldehyde. 



Formaldehyde penetrates very slightly beneath exposed 

 surfaces so that everything to be disinfected should be completely 

 exposed. Openings about windows and doors should be carefully 

 plugged up and sealed with strips of paper. Mechanical cleansing 

 supplemented by application of i-iooo solution of mercuric 

 chloride to floors and walls should follow the fumigation. The 



