202 MANUAL OF BACTERIOLOGY. 



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 paraform. 

 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 slowly through the escape- 

 ment-tube, which has meanwhile been passed through the key- 

 hole. About thirty minutes are required to discharge all the 

 gas from 500 c.c. of solution. If the temperature has not been 

 allowed to go above 135° C, the gas will contain but little 

 moisture and possess its maximum efficiency. 



Schering Lamp. — In this form of lamp formaldehyde is 

 generated by the decomposition of paraform or paraformalde- 

 hyde, a polymeric modification of formaldehyde, occurring as 

 a white salt. It is decomposed by heat, giving off formaldehyde 

 gas. It is placed on the market in the form of tablets, each 

 one of which yields a definite amount of gas. The lamp 

 consists of a small iron tray for the reception of tablets, 

 and so arranged above the heating apparatus that sufficient 

 draught is created to carry off the gas as rapidly as formed. In 

 operating, a sufficient number of tablets are placed on the tray, 

 the lamp lighted and placed in the room to be disinfected. 



Methyl-alcohol Lamps. — Several of these lamps are on the 

 market, all operating on the well-known principle of the oxida- 

 tion of wood-alcohol to formaldehyde when the alcohol is 

 vaporized by projection against a heated, platinized, asbestos 

 disk. In operating such an apparatus, the alcohol is lighted 

 until the asbestos disk becomes hot. The flame is then ex- 

 tinguished; the heat from the disk is sufficient to vaporize the 

 alcohol, which undergoes oxidation and keeps the disk at a red 

 heat. When the apparatus is operating in a satisfactory manner, 

 the room is closed and disinfection allowed to proceed. It 

 must be said, however, that it is difficult to estimate or control 

 the amount of formaldehyde evolved in generators of this type. 



