90 



BIOLOGY AND TECHNIQUE 



thermometer. The whole apparatus is adjusted upon a stand and set 

 over a kerosene lamp. Into the chamber is put about one-half to three- 

 quarters its capacity of 40 per cent formaldehyde (commercial formalin) 

 containing 15-20 per cent calcium chloride. The solution used should 

 be free from methyl alcohol, since this leads to the formation, with 

 formaldehyde, of methylal, which is absolutely without germicidal 

 action. The flame is Ughted and the exit tube kept closed until the 

 pressure gauge indicates a pressure of three atmospheres. Then the 

 vapor is allowed to escape through the tube. For a room of about 3,000 

 cubic feet Trillat advises the continuance of the gas flow for about an 

 hour. The method is not uniformly reliable. 



A method which has found much favor is that in which glycerin— 

 usually in a concentration of 10 per cent — is added to formalin. Ac- 

 cording to Schlossmann^ the presence of 

 glycerin hinders polymerization. An appa- 

 ratus in which this mixture is conveniently 

 utilized is that of Lentz (see Fig. 12). For- 

 malin with 10 per cent glycerin is placed 

 in the copper tank and heated by a burner. 

 Formaldehyde leaves the nozzle (which can 

 be introduced through the keyhole) mixed 

 in a fine spray with steam. This apparatus 

 has been favorably endorsed by the War De- 

 partment of the United States. 



The so-called Breslau method of generat- 

 ing formaldehyde depends upon the evapora- 

 FiG. 12. — Lentz Formalin tion of formaldehyde from dilute solutions, v. 

 Apparatus. Brunn ^ claims that where formalin in 30 to 40 



per cent strength is evaporated, water vapor 

 is generated more rapidly than formaldehyde is liberated, and a 

 concentration leading to polymerization occurs. If, however, dilu- 

 tion is carried out until the formaldehyde in the solution is not 

 more than 8 per cent, the generation of water vapor and formaldehyde 

 takes place at about equal speed and no concentration occurs. Schloss- 

 mann 1 furthermore claims that polymerization in the vaporized formal- 

 dehyde does not occur if sufficient water vapor is present — a principle 

 which may also contribute to the efficiency of the Breslau method. 

 In practice, the apparatus devised by v. Brunn (Fig. 13) consists of a 



'■Schlossmann, Munch, med. Woch., 45, 1898. 

 2 V. Brunn, Zeit. f . Hyg., xxx, 1899. 



