DISINFECTANTS AND ANTISEPTICS. 203 



slowly through the escapement-tube, which has meanwhile 

 been passed through the keyhole. About thirty minutes 

 are required to discharge all the gas from 500 c.c. of solu- 

 tion. 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. This lamp is intended to utilize para- 

 form or para-formaldehyde, a polymeric modification of 

 formaldehye, occurring as a white salt. It is decompos- 

 able by heat, yielding 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 oxidation of wood-alcohol to formaldehyde when the 

 alcohol is vaporized by projection against a heated, plati- 

 nized, asbestos disk. In operating such an apparatus, the 

 alcohol is lighted until the asbestos disk becomes hot. The 

 flame is then extinguished; the heat from the disk is suffi- 

 cient 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 form- 

 aldehyde evolved in generators of this type. 



Formaldehyde Candles. Mixtures of para-formaldehyde 



and paraffin or other combustibles, which may be moulded 



into candles, each enclosed in a tin case, make a convenient 



apparatus to generate formaldehyde gas for room disinfec- 



18 



