8 
they made determinations of the percentage of gas liberated and tests 
of its properties as a disinfectant. Their results indicated this method 
of liberating the gas to be an efficient as well as an ideal one as regards 
simplicity and rapidity. 
As the published reports of almost innumerable experiments with 
formaldehyde give such contradictory results, a further study of this 
question by us has resulted not only in explaining the reason of these 
contradictory results, but also has developed distinct limitations to 
the use of the gas as a disinfecting agent. 
Tor comparison with the formalin-permanganate method many 
experiments under similar conditions were also carried out with each 
of the other well-known methods of obtaining formaldehyde gas. 
namely, the retort, autoclave, generating lamp, sheet-spraying, and 
foimajm-aluminum sulphate-lime methods. 
In order to make our comparisons complete, it was necessary to 
know, in addition to the relative power for destroying microorganic 
life, the quantity of formaldehyde gas present in the atmosphere of 
the room: or. in other words, the yield of gas from a definite amount 
of formalin by the various methods employed. A room was chosen 
which afforded special advantages for conducting chemical as well as 
bacteriological experiments. Quantitative chemical determinations 
of the percentage of gas hberated were made simultaneously with 
bactericidal tests by drawing a definite volume of air from the room 
through an absorbing solution and determining the amoimt of for- 
maldehyde absorbed. 
Our method of making the bacteriological exposures in the experi- 
ments in the room differs somewhat from those usually employed by 
other experimenters. The difference consists principally in having a 
room provided with special apparatus, so that the cultures of the differ- 
ent organisms can be introduced into and removed from the formalde- 
hyde in the room and planted in bouillon whenever desired. This en- 
abled us to ascertain almost exactly the time that a given charge of for- 
maldehyde required to exert its germicidal action upon the different 
organisms exposed. By making the chemical determinations simul- 
taneously with the bacteriological tests the quantity of formaldehyde 
per cubic foot of air in the room at certain stages of the experiment 
was ascertained. The results of a few experiments in this room 
showed that the formalin-permanganate method, besides being rapid 
and simple, compared very favorably with the retort and auctoclave 
methods as regards the percentage of formaldehyde gas hberated 
and its power to destroy microorganic life. 
A request was made of the local management of the Pullman Com- 
pany for the use of some of their cars for experimental purposes, 
which was cheerfully granted. The work was taken up in railroad 
