65 
EXPERIMENT NO. 40. 
Formalin-aluminum sulphate-lime method. 
Formalin, 600 c. c. 
Solution of aluminum sulphate in water (proportion of 50 grams to 100 c. c. of water), 300 c. c. 
Unslaked, lime (in small particles), 2,000 grams. 
Capacity of room, 2,000 cubic feet. 
Quantity of formaldehyde used per cubic foot, 0.107 gram. 
Yield of formaldehyde undetermined. 
Weather: Clear; light wind. 
Tempera- 
ture. 
Relative 
humidity. 
Absolute 
humidity 
(grams per 
cubic foot). 
Before mixing formalin, aluminum sulphate, and lime 
After 10 minutes 
° F. 
69 
69 
70 
Per cent. 
47 
67 
64 
3.63 
5. 17 
5. 10 
After 3 hours 
Time of exposure of organism counted from time of mixing the formalin-aluminum solution and lime. 
[4- means growth; — , no growth.] 
Organism. 
How exposed. 
B. pyocyaneus . . . 
B. coli communis 
B. subtilis 
B. pyocyaneus . . . 
B. coli communis 
B. subtilis 
Glass 
do 
do 
Wilson method 
Filter paper. . . 
do 
Time of exposure in minutes, 
and results. 
10 
20 
30 
45 
60 
90 
120 
180 
4- 
4- 
+ 
4- 
+ 
+ 
+ 
+ 
+ 
+ 
4- 
.... 
4- 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
4- 
4- 
4- 
4- 
+ 
+ 
+ 
+ 
4- 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
The percentage of formaldehyde found in experiment No. 38 was 
low; but, as the temperature and humidity were comparatively high, 
the organisms, including the spores of B. subtil s, were destroyed in 
rather a short time. 
In experiment No. 39 the temperature and humidity were not so 
high as in the previous experiment, and consequently the killing 
power of the formaldehyde was much diminished. The spores of 
B. subtilis exposed on filter paper were not killed within 3 hours. 
There is certainly nothing in the results of this experiment to indicate 
that the addition of 300 c. c. of water was of any advantage for disin- 
fection purposes. 
A low humidity affects the germicidal power of the formaldehyde 
in this method to about the same extent as it does in the other meth- 
ods. This is shown in experiment No. 40, humidity 47 per cent, in 
which the only organism killed 'was B. 'pyocyaneus exposed on glass. 
This method has nothing to recommend it especially for disinfec- 
tion purposes unless it is the amount of moisture given off. This is 
about the same as with the formalin-permanganate method; but, as 
has been mentioned above, it is an open question what role this form 
of moisture plays in disinfecting with formaldehyde. The percentage 
