280 STERILIZATION, ANTISEPSIS AND DISINFECTION 
In the past formaldehyde was liberated from its aqueous solution 
in the gaseous state in complicated retorts, autoclaves or lamps of 
special design. Much simpler methods have been evolved, which are 
now used almost exclusively in practical gaseous disinfection. Of 
these the permanganate method and the "sheet-volatilization method" 
are the most widely used; the former possesses the dual advantage 
of a quick liberation of the entire available amount of disinfectant, 
and very simple apparatus; the latter is advantageous when a gradual 
evolution of gas and prolonged exposure to its action is desired. 
The Permonganate MetJiod.—When formalin is poured upon crystals 
of potassium permanganate, an energetic reaction with the evolution 
of sufficient heat to boil the liquid takes place. Formaldehyde gas 
and heated water vapor are evolved. The entire process requires 
but a few minutes, and when 2 parts of formalin to 1 part of per- 
manganate are used the residue is small in amount and practically dry 
and free from reactive substances. 
Ten ounces of formalin and 5 ounces of permanganate of potash 
crystals are required for each 1000 cubic feet of space to be disinfected. 
The temperature must be not less than 60° F., and the humidity must 
be at least 60 per cent for successful results. It is convenient to place 
the permanganate in a 3-gallon, galvanized-iron pail with flaring sides, 
because the reaction between permanganate and formalin is attended 
with considerable spattering. It is also advisable to place 2 or 3 layers 
of heavy paper under the pail, of sufficient size to project 2 feet at least 
in all directions, or better, to place a galvanized-iron plate of similar 
dimensions under the pail to catch all the liquid which is ejected from 
the pail during the process of evolution of the gas. For successful 
disinfection, all closets, drawers and alcoves should be opened as 
freely as possible; doors, windows and fireplaces leading to the exterior 
should be tightly closed. The room should be left closed and undis- 
turbed for at least four hours. 
The Sheet Volatilization Method.— This method requires no appara- 
tus except sheets, and some mechanical device for spraying formalin 
upon the sheets. The conditions of moisture and humidity and the 
same general preparation of the room as for the potassium perman- 
ganate formalin method must prevail. 
Sheets are hung upon tightly stretched cords or other similar sup- 
port, in such a manner that they rest at an angle of about 45 degrees 
with the perpendicular. They are wet with warm water, are "wrung 
out" to remove the excess, and sprayed with formalin in the propor- 
tion of 10 ounces to each 30 square feet of surface. One sheet (30-feet 
square) is sufficient for each 1000 cubic feet of room space. 
The evolution of formaldehyde is slower with the sheet method than 
with the permanganate method, but equally efficient disinfection is 
obtained if the room is kept closed eight hours. 
2. Paraform.— Paraform is a polymer of formaldehyde; it is a white 
solid which is readily ignited, and burns with a bluish flame. It 
