Insecticides and Related Substances. 311 



feet of space in the first two cases and twice as much must be used 

 in the permanganate method. This disinfectant also acts as a 

 deodorant. 



Paraform is a condensed form of formaldehyde put up as a 

 powder or as pastils. Two ounces of paraform liberate gas suf- 

 ficient to disinfect 1000 cubic feet of space. 



Mercuric chloride or corrosive sublimate is a poisonous, white, 

 crystalline salt. It is usually put up in tablet form with am- 

 monium chloride to facilitate dissolving in water. Strengths of 

 1 to 500 to 1 to 1000 are used, the greater strength being neces- 

 sary to destroy bacterial spores. This is a powerful stomachic 

 poisoning and must be handled with care. It forms insoluble 

 compounds with proteins and hence raw eggs and milk are given 

 as antidotes. On account of its chemical affinity for proteins, 

 unless liberally used it has little disinfecting power when applied 

 to excreta, blood and similar protein containing materials. Solu- 

 tions of this salt should be used only in glass or earthern ware, 

 as it reacts with tin and other common metals. 



Chloride of lime (bleaching powder) is both a disinfectant and 

 deodorizer. It is prepared by passing chlorine gas over slaked 

 lime. The compound decomposes rapidly on exposure to the 

 air and hence is put up in hermetically sealed containers and is 

 reliable only when freshly removed from these. 



Carbolic acid is a derivative of benzene, a hydrocarbon which 

 forms the basis of the coal tar dyes. At ordinary temperatures 

 it has the crystalline form of long, white needles. One part of 

 water to 9 parts of the crystals produces a liquid, in which form 

 it is commonly dispensed. By dissolving in warm water a solu- 

 tion of slightly over 6 per cent carbolic acid can be made. This 

 is used as a spray and wash. Crude carbolic acid is a crude prep- 

 aration from coal tar distillation, the latter substance being the 

 liquid by-product in the production of gas and coke from coal. 

 This disinfectant is a mixture of various coal tar oils and so- 

 called "cresylic acid/' and contains little or no true carbolic 

 acid. The disinfecting power is due to cresols of the "cresylic 



