66 
of formaldehyde liberated by this method is less than half that ob- 
tained by the formalin-permanganate method. The latter method 
is also simpler and more easily conducted than the former. For 
practical disinfection some of the other methods, notably the forma- 
lin-permanganate, are superior to the formalin-aluminum-sulphate- 
lime method; consequently, further experiments with the latter 
method seemed unnecessary, although under favorable conditions it 
may be used with very good results. 
EXPERIMENTS IN A LARGE BOTTLE WITH THE FORMALIN- 
PERMANGANATE METHOD. 
As the changes in climatic conditions caused variations in the 
results of the experiments performed in the room, some experiments 
were performed in a large bottle, in which certain influences would 
be either eliminated or more amenable to control. 
Furthermore, the special purpose of these experiments precluded 
the possibility of conducting them in a room of any character. This 
purpose may be briefly summarized as follows: (1) To determine 
with the formalin-permanganate method under different conditions 
the quantity of formaldehyde liberated and also the quantity left 
in the residue in the generator; (2) to determine the minimum relative 
humidity and lowest temperature at which formaldehyde disinfection 
is practicable. 
Chemical determinations. — The chemical experiments were carried 
out in two bottles, one holding a trifle over 24 liters (0.85 cubit foot), 
the other very nearly 18 liters (0.63 cubic foot). The mouths of the 
bottles were 2.75 inches wide and w^ere closed with tight-fitting corks, 
the pores of which were sealed with melted paraffin. 
A porcelain crucible holding 24 c. c. was fitted into an excavated flat 
cork, which was suspended in a stirrup of thin twine. 
The formalin was practically 40 per cent by volume, as determined 
by the Blank and Finkenheimer hydrogen dioxide method. The 
quantity to be used in an experiment, usually 0.7 c. c., was carefully 
measured from a slender pipette in which 0.1 c. c. made a volume 1.7 
cm. long. The formalin was used undiluted in some experiments and 
in others a definite quantity of water was added to it before mixing 
with the permanganate. 
I. EXPERIMENTS WITH UNDILUTED FORMALIN AND PERMANGANATE. 
Method of 'procedure for determining the percentage of gas liberated . — 
About 40 c. c. of approximately decinormal potassium cyanide solu- 
tion were measured from a burette into the bottle and about 50 c. c. of 
water added. The liquid was then rolled over the side of the bottle 
to produce a greater absorbing surface. Then the crucible containing 
