56 
EXPERIMENT NO. 31— Continued. 
[+ means growth; — no growth.] 
This method is very reliable for surface disinfection during warm 
weather provided the sheets are properly sprayed. Not over 300 c. c. 
of formalin should be used for every 30 square feet of sheet surface. 
The percentage of formaldehyde remains comparatively high during 
a relatively long time. The maximum of 30 per cent seems to be 
reached after approximately 4 hours standing, but at the end of 24 
hours, 20.8 per cent was still found. 
This is quite different from the other methods in which the per- 
centage of formaldehyde begins to diminish by leakage from the 
moment the charging is finished. Evaporation maintains the hu- 
midity at a fairly high percentage which, with the constancy of libera- 
tion of formaldehyde, makes the method very applicable when a large 
exposure is required. On the other hand the influence of a low tem- 
perature upon the results obtained with this method is more marked 
than with any other methods tried. It was found that at a temperature 
of 43.5° F. very little formaldehyde is liberated and that the formalin 
gradually polymerizes on the sheets. This of course makes the use of 
this method for disinfection purposes absolutely impracticable during 
cold weather. 
VI. THE GENERATING LAMP. a 
The lamp used in this work is one of the various lamps devised for 
the purpose of generating formaldehyde by oxidation of methyl 
alcohol. This is brought about by means of incandescent platinized 
asbestos, which has the power of causing the oxj’gen of the air and 
methyl alcohol vapor to combine according to the following reaction : 
CH 4 0 + O = HCHO + H 2 0. 
methyl formal- 
alcohol. dehyde. 
The platinized asbestos is heated by first burning some of the alco- 
hol, after which the flame is extinguished. Alcohol continues to 
vaporize and the heat produced in the oxidation maintains the tem- 
perature of the apparatus. The time usually allowed for the exhaus- 
tion of the lamp is about 2 hours. 
a The lamp used is manufactured by the Kuhn Formaldehyde Generator Co., Alexandria, , 
Va. 
