202 MANUAL OF BACTERIOLOGY. 



fectant is by far the most important application at the 

 present time. 



Harrington's investigations have shown that an atmosphere produced 

 by vaporizing 435 c.c. of formalin (40 per cent, aqueous solution of 

 the gas) in 1000 cubic feet of air space, equivalent to i quart to a room 

 15 feet square and 10 feet high, will destroy all exposed organisms in 

 half an hour ; when protected by one fold of cotton-cloth, an exposure 

 of one and one-half hours is necessary. In a perfectly dry atmosphere 

 the gas penetrates slightly, and will disinfect through one layer of 

 cotton-cloth; in a moist atmosphere no penetration can be obtained. 



In vaporizing the gas many methods have been em- 

 ployed. Simple evaporation of solutions without heat 

 cannot be relied upon, for the solid, polymerized para- 

 formaldehyde is easily formed under these circumstances. 

 Better results can be obtained with the aid of heat, although 

 polymerization is apt to occur unless evaporation is rapid. 

 To produce the best results it has been found necessary to 

 use special forms of lamps or generators for its production, 

 a few of which are mentioned below. 



Sanitary Construction Company's Lamp. This lamp 

 consists of a tank to hold the formaldehyde solution, and a 

 spiral tube by which the solution is slowly conducted through 

 a flame and vaporized. The necessary amount of solution 

 is placed in the tank and the apparatus started, outside 

 the room, the gas being conducted through the keyhole by 

 a suitable tube. 



Trillat Autoclave. A small silver-lined pressure-boiler, 

 fitted with lamp, safety-valve, pressure-gauge, thermome- 

 ter and escapement-tube. The necessary amount of form- 

 aldehyde solution is placed within the apparatus, together 

 with an equal amount of 20 per cent, solution of calcium 

 chloride ; the addition of the latter salt is to prevent forma- 

 tion of the solid polymeric modification, the so-called para- 

 form. The autoclave is closed and heated from below to 

 a temperature of 135 C. The escapement-valve is then 

 opened carefully and the gas allowed to enter the room 



