30 
with formaldehyde can not be stated exactly; but the indications are 
that too much dependence must not be placed in it. No doubt it is 
an advantage, but it does not seem to answer the purpose so well as 
the natural humidity of the atmosphere. 
The special points of advantage of the formalin-permanganate 
method of evolving formaldehyde are that it is simple in operation, 
no special apparatus is required, it is economical both as to time and 
money, it produces considerable moisture, and it liberates a large 
quantity of formaldehyde in a relatively short time. This last fact is 
of special advantage, since with an ordinary room no pasting of 
cracks, etc., is required. For disinfection purposes it is better to 
have a large quantity of formaldehyde with a short exposure than a 
small quantity with a long exposure. A large quantity of formalde- 
hyde and a high temperature and humidity all assist penetration. 
II. DILUTED FORMALIN AND PERMANGANATE METHOD. 
A number of experiments were made with formalin diluted with 
various quantities of water and different weights of permanganate. 
The purpose in adding the water was to increase, if possible, the 
amount of moisture given off. 
In each experiment 600 c. c. of formalin were used, to which were 
added, before mixing with the permanganate, 300 c. c. of water in 
some of the experiments and 600 c. c. in the others. 
For every 100 c. c. of water used an additional 25 grams of perman- 
ganate were required in order to obtain a residue fairly free from liquid. 
The time required for the reaction to begin was slightly diminished 
in this method as compared with the undiluted formalin-permanga- 
nate method. The ebullition, too, seemed to be more violent. 
Except for the differences above noted, the method of procedure in 
charging the room was the same as with the undiluted formalin-per- 
manganate method already described. 
Chemical determinations . — The interval between setting off the 
charge and beginning to draw air, the volume of air drawn (10 liters) 
and the time required to draw it were about the same as in Table 1. 
In several instances two experiments were made simultaneously with 
5 and 10 liters of air respectively. 
