75 
The question might arise whether absolutely all of the moisture was 
removed from the bottle by the calcium chloride after 1 hour expo- 
sure; but from the known chemical affinity of this substance for 
water it would seem that all of it was absorbed. 
If all the moisture was removed from the bottle by the calcium 
chloride, the idea that once prevailed, namely, that formaldehyde 
can not exist in a perfectly dry state, is disproved. 
A comparison of the percentage of humidity required in these 
experiments with that required in the room experiments (p. 29), 
would seem to indicate that the moisture given off by the process of 
liberation in the latter experiments is of much less importance than 
the moisture in the air before the experiment is started. 
It is not so much the absolute as the relative humidity that is nec- 
essary in formaldehyde disinfection. For example, the action of an 
ordinary quantity of formaldehyde is strongly germicidal in the pres- 
ence of 5.586 grains (0.36 gram) of moisture per cubic foot at a tem- 
perature of 70° F. (relative humidity 70 per cent), but is almost inert 
in the presence of 6.85 grains (0.443 gram) per cubic foot at a tempera- 
ture of 95° F. (relative humidity 40 per cent). 
By referring to Table 7 it will be seen that a large quantity of for- 
maldehyde was removed from the bottle in the process of drying. It 
may be assumed from our experimental determinations that before 
drying, the bottle contained 36.71 per cent of the formaldehyde theo- 
retically present in the quantity of formalin used. By drying 1 hour 
with calcium chloride the quantity of formaldehyde was reduced to 
about 20.5 per cent and after 2 hours to 14.76 per cent. 
To show the germicidal power of a reduced quantity of formalde- 
hyde in the presence of a high humidity and temperature two experi- 
ments were done, using one-fourth the original quantities of formalin 
and permanganate used in Tables 8 and 9, namely, formalin 0.25 c. c. 
and permanganate 0.125 gram. 
In one experiment with a relative humidity of 61 per cent, tempera- 
ture 26° F., B. coli communis was killed within 30 minutes. In the 
other, with relative humidity of 59 per cent, temperature 60° F., the 
same species was killed within the same time. B. subtilis , exposed in 
both experiments at the same time as B. coli communis , were not 
killed within 2 hours. 
Two more experiments were performed in which one-eighth the 
original quantities of formalin and permanganate were used, namely, 
formalin 0.125 c. c. and permanganate 0.0625 gram. In one, with a 
relative humidity of 75 per cent, temperature 74° F., B. coli com- 
munis was kffied within 30 minutes, while in the other, with a relative 
humidity of 59 per cent, temperature 70° F., the same species was 
killed within one hour. B. subtilis , exposed at the same time as B. 
coli communis, was not killed in either experiment within 2 hours. 
