63 
He dissolves 20 to 25 pounds of commercial aluminum sulphate in 5 
gallons of hot water and mixes this solution with 15 gallons of 40 per 
cent formaldehyde solution. Eight fluid ounces of this mixture and 
1 pound of lime are used for 1,000 cubic feet. He recommends that 
the lime be used in small particles and that it should slake rapidly in 
cold water. We used the method practically as recommended by 
Walker. 
Aluminum suphate was added to hot water in the proportion of 50 
grams of the former to 100 c. c. of the latter. For an experiment 300 
c. c. of this solution, 600 c. c. of formalin, and 2,000 grams of unslaked 
lime were usual] y used. Before using the lime it was broken into 
small particles and placed in a large bucket in the room. When 
ready to start, the formalin and aluminum sulphate solution were 
mixed and poured over the lime. The lime began to slake in a few 
minutes and continued about 20 minutes, during which time consid- 
erable formaldehyde, steam, etc., were given off. At the end of this 
time the process of liberation appeared to be completed. 
Chemical determinations were made in the usual way, allowing about 
40 minutes to elapse after starting an experiment before beginning to 
draw air from the room. As it was soon found that the percentage 
of formaldehyde liberated by this method is relatively low, only a few 
experiments were done. About 14 per cent was found, which is less 
than half that liberated by several of the other methods. After the 
experiment was over ( 2 hours) the lime was found completely slaked 
and in a perfectly dry state. 
A summary of conditions and results is given in each of the follow- 
ing experiments performed for the purpose of determining the disin- 
fecting value of this method : 
EXPERIMENT NO. 38. 
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. 
Quantity of formaldehyde found per cubic foot, 0.01498 gram. 
(Determination made by drawing air from room beginning 40 minutes after mixing the formalin- 
aluminum solution and lime.) 
Yield of formaldehyde, 14 per cent. 
Weather: Practically no wind; warm and rainy. 
Tempera- 
ture. 
Relative 
humidity. 
Absolute 
humidity 
(grams per 
cubic foot) . 
Before mixing formalin, aluminum sulphate, and lime 
° F. 
' 87 
Per cent. 
66 
8. 92 
After 10 minutes 
87.5 
85 
11.67 
After 20 minutes 
87.5 
83 
11.39 
After 2 hours 
88.0 
81 
11.29 
Time of exposure of organism counted from time of mixing the formalin-aluminum solution and lime. 
32507 — No. 27 — 06—5 
