28 
The time to kill is comparatively longer with the Wilson method of 
making exposures than with the other methods; this fact may he 
attributed to the lower humidity diminishing the power of penetration 
of the formaldehyde. 
The following two experiments show the inefficient results obtained 
when the temperature is comparatively low. No doubt slightly bet- 
ter results would have been obtained in these two experiments if the 
humidity had been higher, say 90 per cent. In Experiment No. 7, 
temperature 62° F., some polymerization of the formaldehyde took 
place, as was evidenced by the hazy appearance of the air in the room 
and the decreased percentage of formaldehyde obtained; but it was 
not nearly so marked as in Experiment No. 8, temperature 52° F. In 
the latter experiment quite a deposit of paraform was observed in the 
room after opening. 
EXPERIMENT NO. 7. 
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, 0.02685 gram. 
(Determination made by drawing air from the room, beginning 15 minutes after mixing the 
formalin and permanganate and consuming 1 hour 15 minutes in the drawing.) 
Yield of formaldehyde, 25.1 per cent. 
Weather: Cloudy, no wind. 
Tempera- 
ture. 
Relative 
humidity. 
Absolute 
humidity 
(grams per 
cubic foot) . 
° F. 
Per cent. 
Before mixing HCIIO and KMnO-i 
62 
55 
3.37 
After 10 minutes 
62 
74 
4.54 
After 3 hours 
62 
64 
3.93 
See note, Experiment No. 1. 
[ + means growth ; — no growth.] 
Organism. 
B. coli communis . 
B. typhosus 
B. subtilis 
B. coli communis. 
B. subtilis 
How exposed 
Filter paper 
do 
do 
Wilson method. 
do 
Time of exposure in minutes, and 
results. 
10 
20 
30 
45 
60 
90 
120 
180 
+ 
+ 
+ 
+ 
+ 
— 
— 
— 
— 
+ 
+ 
+ 
+ 
+ 
+ 
- 
- 
+ 
+ 
+ 
+ 
+ 
+ , 
+ 
+ 
