108 BIOLOGY AND TECHNIQUE 



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 69 furthermore claims that poly- 

 merization 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 practice, 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 purposes 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 (commercial 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 evaporated. This, according to v. Brunn, is about 

 one-quarter of the volume of formalin solution used. By using 1.5 liters 

 of 8 per cent formalin for each 1,000 cubic feet of space, this apparatus 

 is said to yield a concentration of formaldehyd of about 25 grams to the 

 cubic meter. 



To do away with the use of liquid, a method has been devised 

 which depends on principle upon the breaking up by heat of the 

 solid polymer of fortnaldehyd (trixymethylene). 



The apparatus (trade name, "^chering's Paraform Lamp") as described 

 by Aronson 71 consists of a cylindrical mantle of sheet-iron placed upon a 

 stand and supplied below with an alcohol lamp. Set into the top of the 

 mantle is a small chamber, into which 1 gram tablets of trioxymethylene 

 are placed. The alcohol lamp, so placed that the wicks project but slightly 

 to avoid overheating is lighted, and the formalin generated passes out 

 through slits in the upper case, mingling with the water vapor and other 

 gases liberated by the alcohol flame. The more modern devices have water- 

 boiler attachments to insure sufficient moisture. Two tablets are sufficient 

 for the fumigation of about thirty-five cubic feet, and 2 c.c. of alcohol 

 are filled into the lamp for each tablet. One hundred to one hundred and 

 fifty tablets are usually enough for the ordinary room. 



A simple method of generating formaldehyd is that which is 

 known as the "lime method/' In a wide shallow pan 40, per cent 



"Aronson, Zeit. f. Hyg., xxv, 1897. 



