39 
EXPERIMENT NO. 17. 
Dilute formalin-permanganate method. 
Formal’'n, 600 c. c. 
Water, 600 c. c. 
Permanganate, 450 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, 0.01234 gram. 
(Determination made bybirawing air from the room, beginning 15 minutes after mixing the for- 
malin and permanganate, and consuming 1 hour 30 minutes in the drawing.) 
Yield of formaldehyde, 11.53 per cent. 
Weather: Cloudy, north wind. 
Tempera- 
ture. 
Relative 
humidity. 
Absolute 
humidity 
(grams per 
cubic foot). 
° F. 
Per cent. 
Before mixing HCKO and KMnOi 
41 
55 
1.62 
After 10 minutes 
40 
92 
2.51 
\fter 3 hours 
41.5 
61 
1.83 
See Note, Experiment No. 9. 
[+ means growth; — no growth.] 
Organism. Row exposed. 
B. coli communis 
B. typhosus 
B. subtilis 
B. coli communis 
B. subtilis 
Filter paper . . . 
do 
do 
Wilson method 
do 
Time of exposure in minutes, 
and result. 
10 
20 
30 
45 
60 
90 
120 
180 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
+ 
For practical disinfection purposes the results of the undiluted and 
diluted formalin-permanganate methods do not, on the whole, differ 
materially. The relative humidit} r is increased in about the same 
proportions in the two methods and the organisms killed in about the 
same time. The only advantage in diluting the formalin seems to be 
when working at a reduced temperature. Then polymerization does 
not seem to take place as much as wbien the water is not added. This 
may account for the relatively larger percentage yield of formalde- 
hyde, as w T ell as its more efficient germicidal action in experiments 
Nos. 16 and 17 as compared with experiments Nos. 7 and 8. 
Comparing experiment No. 16, in which 300 c. c. of water were 
added, with experiment No. 17, in which 600 c. c. of w T ater were 
added, it will be seen that the addition of the former quantity of 
water gave slightly better germicidal results than the latter. This 
would indicate that there is nothing to be gained by diluting the 
quantity of formalin with more than half its volume of water. This 
statement, however, must not be construed as recommending the 
diluted formalin-permanganate method for disinfection purposes 
