29 
EXPERIMENT NO. 8. 
Formalin-permanganate method 
Formalin, 600 c. c. 
Permanganate, 300 grams. 
Capacity of room, 2.000 cubic feet. 
Quantity of formaldehyde used per cubic foot, 0.107 gram. 
Quantity of formaldehyde found per cubic foot, 0.01186 gram. 
(Determination made by drawing air from the room, beg innin g 15 minutes after mixing the 
form alin and permanganate and consuming 1 hour 20 minutes in the drawing.) 
Yield of formaldehyde, 11.09 per cent. 
Weather:. Rainy, very little wind. 
Tempera- 
ture. 
Relative 
humidity. 
Absolute 
humidity 
(grams per 
cuDic foot). 
° F. 
Per cent. 
Before mixing HCHO and KMnOt 
52 
63 
2. 75 
After 10 minutes 
51 
78 
3.29 
After 3 hours 
50 
71 
2.89 
See note, Experiment No. 1. 
[ + means growth ; — no growth.] 
Organism. 
How exposed. 
Time of exposure in minutes, and 
results. 
10 
20 
30 
45 
60 
90 
120 
180 
B. coli communis 
Filter paper 
+ 
+ 
+ 
B. typhosus 
do 
+ 
4- 
B. subtilis 
do 
4" 
+ 
+ 
+ 
+ 
+ 
+ 
— 
B. coli communis 
Wilson method 
+ 
+ 
4“ 
+ 
+ 
+ 
_L 
4" 
B. subtilis 
do 
+ 
+ 
r 
+ 
+ 
+ 
+ 
+ 
The results with the formalin-permanganate method are all that 
can be desired for practical disinfection purposes, provided the tem- 
perature and relative humidity are comparatively high. Under 
these conditions no particular advantage is gained, especially for sur- 
face disinfection, by having a large quantity of formaldehyde gas 
present, as is shown by the above experiments in which different 
quantities of formalin were used. With a low temperature or humid- 
ity formaldehyde is practically useless as a disinfectant. 
The niinimum percentage of humidity and lowest temperature at 
which disinfection with formaldehyde can be accomplished can not 
be stated accurately, as the one depends to a limited extent upon the 
other. However, it seems that for practical disinfection with the 
formalin-permanganate method the humidity should not be below 60 
or 65 per cent and the temperature not below about 65° F. The 
former refers to the percentage of humidity in the air of the room 
before starting an experiment. In our experiments the humidity in 
the air of the room was increased 15 to 23 per cent in the different 
experiments by the moisture given off from the formalin-permanga- 
nate. Just what part this increase in humidity plays in disinfecting 
