116 EFFECT OF CHEMICALS ON BACTERIA 



from 5 to 12 or more pounds of bleaching powder is used to each 

 million gallons of water. It cannot be detected by the sense of taste 

 provided the amount does not exceed 25 pounds to 1,000,000 gallons. 

 Waters containing considerable organic material of any kind give 

 rise to amins, chloramins, and other compounds with unpleasant 

 flavors. The method, however, is cheap, reliable, efficient, harmless, 

 and easy of application. 



Formaldehyd is one of the best volatile antiseptics. If used in 

 sufficient concentration and under proper conditions it can be 

 depended upon for surface disinfection. Although more penetrating 

 than sulphur dioxid, it is not sufficient to depend upon in deep layers 

 of cloth and similar bodies. It does not rot nor bleach fabric nor 

 tarnish metal as does sulphur dioxid. Moreover, formaldehyd 

 unites with nitrogenous substances forming new chemical compounds 

 which are both sterile and odorless. It is, therefore, good both as a 

 germicide and as a disinfectant. 



Although there are numerous methods of using, one of the best 

 is that recommended by the Pennsylvania Department of Public 

 Health: 



Sodium dichromate 10 oz. 



Formalin 16 oz. 



Commercial sulphuric acid 1^ oz. 



The sulphuric acid is added to the formalin and the mixture poured 

 over the crystals of sodium dichromate causing immediate liberation 

 of formaldehyd gas. Five hundred c.c. of formalin and 250 gm. of 

 sodium dichromate should be used for each thousand cubic feet of air. 

 The floor should be protected against the heat by placing the bucket 

 upon a brick or other suitable device. 



Sulphur Dioxid. Sulphur dioxid is not very efficient as a germicide; 

 it is, however, an effective insecticide. It is also good to use against 

 diseases spread by rats, mice, flies, fleas, mosquitoes, etc. 



Its action as a germicide depends upon the presence of moisture. 

 The dry gas is practically inert against bacteria. It cannot be 

 depended upon where penetration is required, its action being merely 

 upon the surface. It does not kill spores. Moreover, it is a bleaching 

 agent and tarnishes metals. In sterilization by means of sulphur, 

 time is an important factor. The things to be disinfected should 

 be exposed for eight hours to an atmosphere of at least 4 per cent, 

 by volumes of sulphur dioxid gas in the presence of water. This 

 requires the burning of 4 to 5 pounds of sulphur for every 1000 cubic 

 feet of air space. About one-fifth of a pound of water should be 

 volatilized for every pound of sulphur used. 



One method of using it follows : The required quantity of sulphur 

 is placed in a pan which is put into a second larger pan containing 

 water. The sulphur is made into little craters and liberally soaked 



