124 PRINCIPLES OF BACTERIOLOGY 



tion required, the concentration of the gas used, the amount of moisture 

 in the air, the temperature of the air, and the size and shape of the 

 room. For surface disinfection in rooms, when as much as twelve 

 ounces of formalin are used for each 1000 cubic feet, five hours' exposure 

 is amply sufficient, most bacteria being killed within the first few minutes. 

 For the destruction of micro-organisms protected by even a layer of 

 thin covering, double the formalin and double the time of exposure 

 should be allowed, and even then the killing of many species of non- 

 spore bearing bacteria cannot be counted upon in ordinary rooms. 

 When absolutely complete disinfection is demanded, where penetration 

 of gas is required, the goods must be placed in chambers where moderate 

 heat can be added and all leakage of gas prevented. 



Various forms of apparatus can be properly employed to liberate 

 formaldehyde gas for purposes of disinfection. There are two essentials 

 to any good method namely, that the formaldehyde gas is given off 

 quickly, and that there is no great loss by deterioration of the formalin. 



Wood Alcohol. A number of lamps have been devised, all very much 

 on the same principle, though varying somewhat in mechanical con- 

 struction, which bring about the incomplete oxidation of methyl-alcohol 

 by passing the vapors mixed with air over the incandescent metal. 

 Although disinfection can be carried out by the best of these lamps, in 

 our experience none of them up to the present time are satisfactory or 

 economical. They may be very useful as deodorizers in the sick-room 

 or other places. 



The same principle is used efficiently in another form. The vapor 

 of wood alcohol is passed over surfaces of asbestos containing particles 

 of finely divided platinum. This apparatus has given very good results, 

 and for a given amount of disinfection leaves less odor of formaldehyde 

 gas in the room than any other. The apparatus is, however, bulky and 

 expensive. 



Formochloral by the Trillat System. This system consists in heating, 

 under three atmospheres of pressure, a solution of formaldehyde gas 

 in water mixed with 30 per cent, of calcium chloride, known as "formo- 

 chloral," to a temperature of 135 C. (275 F.). It is claimed for this 

 method of producing the gas from formochloral that the polymerization 

 of the formaldehyde is prevented, which would otherwise take place 

 if a solution of formaldehyde were evaporated under ordinary condi- 

 tions, and that thereby the whole of the formaldehyde is obtained in 

 the gaseous state. The addition of any neutral salt aids the process, 

 it is said, but calcium chloride is the best. The results with this apparatus 

 have been satisfactory, but not more so than by other methods. The 

 apparatus is expensive and heavy and therefore unnecessary. 



Formalin by Boiling and Passing the Vapor through a Superheated Coil 

 or Chamber. This system consists in heating the ordinary commercial 

 formalin to a temperature of about 260 C. (500 F.) in an incandescent 

 copper coil or chamber, and allowing the vapors to pass off freely. It is 

 claimed for this method that the degree of heat necessary to break 

 up the polymerized products formed is supplied, and thus a loss of 



