71 
The quantities of formaldehyde found remaining with the residue 
in the porcelain crucible (average 34.08 per cent) agree fairly well 
with the results in experiments IV, V, VII, and VIII, Table 6 (average 
33.50 per cent). 
IV. HUMIDITY AM) TEMPERATURE IN FORMALDEHYDE DISINFECTION. 
The influence and importance of humidity and temperature became 
very evident in many of the experiments, but owing to uncontrollable 
circumstances in the room their minimum limitations, particularly 
of the humidity, could not be closely approximated. It will readily 
be seen that it is of more practical importance to know this in case of 
the humidity than of the temperature, since the former is subject to 
wide variations even within a few hours. For instance, the humidity 
of the atmosphere may be 90 per cent at 8 a. m., 30 per cent at 2 p. m., 
and 90 per cent again at 8 p. m. of the same day. Such variations 
in temperature seldom, if ever, occur in so short a time. As we had 
observed in the room experiments that formaldehyde is inefficient as 
a disinfectant when employed during cold weather, most of the experi- 
ments for determining the minimum limitations of humidity were 
done at ordinary summer temperatures. For conducting the experi- 
ments a large bottle holding 24 liters (0.85 cubic foot) was used. As 
this bottle, the mode of setting off the formalin and permanganate, 
the process of drying with calcium chloride, etc., have already been 
fully described (p. 06), only the more important details will be given 
here, svef ,V; -w • - 
The quantities of formalin and permanganate used were in the pro- 
portion of 1 c. c. of the former to 0.5 gram of the latter. The formalin 
contained about 40 per cent of formaldehyde by volume. The result 
of mixing the formalin and permanganate in the above proportions 
was a vigorous reaction, which, in addition to evolving formaldehyde, 
gave off rather a large quantity of aqueous vapor, which settled on the 
sides of the bottle to such an extent as to make the glass almost non- 
transparent. 
A few experiments easily demonstrated that with a high tempera- 
ture, say 80° F., even a small percentage of formaldehyde with a large 
quantity of moisture, is a most powerful surface disinfectant, killing 
40-day old spores of Bacillus subtilis in a few minutes. 
The object then was to remove the moisture in the bottle by intro- 
ducing a metal tray containing anhydrous calcium chloride, after which 
a definite quantity of water could be injected in the form of aqueous 
vapor. 
Soon after introducing the calcium chloride the moisture from the 
sides of the bottle would disappear. The atmosphere in the bottle 
was assumed to be in a dry condition after about 1 hour, and the tray 
