EFFECT OP CHEMICAL ENVIRONMENT 143 



either in solution or as a gas. It finds extensive use as a 

 fungicide in the destruction of smut spores on certain 

 grains. For the destruction of bacteria it is most commonly 

 used as a fumigant. The formaldehyde gas may be gen- 

 erated either by boiling solutions of the gas, that is, by boil- 

 ing formalin, or from some of the polymers of formalde- 

 hyde, such as paraform. Formaldehyde gas is most efficient 

 in the presence of moisture. Vessels containing formalin 

 may be heated directly over a flame, the formalin may be 

 sprinkled upon sheets and hung about in the room to be 

 fumigated, or the formalin may be poured over a heap of 

 crystals of potassium permanganate in a container that will 

 not be corroded. In the last-named process the heat pro- 

 duced by the oxidation of a portion of the formaldehyde by 

 the permanganate vaporizes the remainder. 



Phenol and the closely related coyipounds are among the 

 most satisfactory of disinfectants for general use. Phenol 

 (CgHjOH) in a 5 per cent solution will destroy most non- 

 spore-producing bacteria in a relatively short time. Some 

 bacterial spores, however, are extremely resistant. The 

 cresols or methyl phenols (CoHiCHgOH) are the chief con- 

 stituents of many of the so-called coal tar disinfectants sold 

 on the market. The cresols are not as soluble in water 

 as is phenol. A saturated solution contains about 2 14 per 

 cent. They are even more effective than is phenol. Fre- 

 quently acids or alkalies are added to the phenols and 

 cresols to increase their disinfecting power. Benzoic 

 acid (CeH^COOH) and sodium henzoate (CeH^COONa), 

 salicylic acid (CeH^OHCOOH), and sodium salicylate 

 (CeH^OHCOONa) have been used frequently as preserva- 

 tives in foods, usually in concentrations of not more than 0.2 

 per cent. Salicylates are generally forbidden in foods under 

 our pure food laws, but benzoates are permitted providing 

 the amount is fairly stated on the label. Some of the 

 so-called canning powders sometimes used by housewives in 



