90 



BIOLOGY AND TECHNIQUE 



L 



tinuance of the gas flow for about an hour, j The method is not uni- 

 formly 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 1 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. 

 This apparatus has been favorably endorsed 

 by the War Department of the United States. 

 The so-called Breslau method of generat- 

 ing formaldehyd depends upon the evapora- 

 tion of formaldehyd from dilute solutions, v. 

 Brunn 2 claims that where formalin in 30 to 40 

 per cent strength is evaporated, water vapor 

 FIG. 12. LENTZ FORMALIN is generated more rapidly than formaldehyd 

 APPARATUS. is liberated, and a concentration leading to 



polymerization occurs. If, however, dilution 



is carried out until the formaldehyd in the solution is not more than 

 8 per cent, the generation of water vapor and formaldehyd take 

 place at about equal speed and no concentration occurs. Schlossmann l 

 furthermore claims that polymerization in the vaporized formaldehyd 

 does not occur if sufficient water vapor is present a principle which 

 may also contribute to the efficiency of the Breslau method. In prac- 

 tice, the apparatus devised by v. Brunn (Fig. 13) consists of a strong 

 copper kettle of about 34 cm. diameter by 7.5 cm. height. This is 

 completely closed except for two openings in the slightly domed top, 

 one of which is the exit vent, the other, laterally placed, is for pur- 

 poses of filling and is closed by a screw stopper. The tank is filled 

 with a solution of formalin of a strength of from 8 to 10 per cent (com- 

 mercial formalin 1:4). The apparatus permits the evaporation of 

 large quantities of fluid in a short time (3 liters in one hour). When 

 the lamp is left in a closed room care should be taken to fill it with 

 a quantity of alcohol proportionate to the amount of fluid to be evap- 

 orated. This, according to v. Brunn, is about one-quarter of the 



1 Schlossmann, Munch, med. Woch., 45, 1898. 

 8 v. Brunn, Zeit. f. Hyg., xxx, 1899. 



