The property of formaldehyde of penetrating all kinds of paper, even when folded together in several layers, may be utilized for a perfect disinfection of books and letters, especially at a temperature of 86° to 122° F. in a closed room. The degree of penetration as well as the disinfecting power of the formaldehyde depend upon the method of generating the gas. Letters, paper in closed envelopes, are completely disinfected only in 12 hours, books in 24 hours at a temperature of 122° F. when 70 cubic centimeters of formochloral—17.5 g. of gas—per cubic meter of space are used. Books must be stood up in such a manner that the gas can enter from the sides. Bacilli of typhoid preserve their vitality longer upon unsized paper and on filtering paper than on other varieties.

There is much difference of opinion as to the disinfecting and deodorizing power of formaldehyde when used to disinfect wooden tierces. While some have found it to answer well, others have got variable results, or failed of success. The explanation seems to be that those who have obtained poor results have not allowed time for the disinfectant to penetrate the pores of the wood, the method of application being wrong. The solution is thrown into the tierce, which is then steamed out at once, whereby the aldehyde is volatilized before it has had time to do its work. If the formal and the steam, instead of being used in succession, were used together, the steam would carry the disinfectant into the pores of the wood. But a still better plan is to give the aide hyde more time.

Another point to be remembered in all cases of disinfection by formaldehyde is that a mechanical cleansing must precede the action of the antiseptic. If there are thick deposits of organic matter which can be easily dislodged with a scrubbing brush, they can only be disinfected by the use of large quantities of formaldehyde used during a long period of time.