Formalin is a forty per cent. aqueous solution of formaldehyde, (Ch2o). It is a colorless, neutral, volatile liquid with a pungent odor and slightly irritating taste. It mixes in all proportions with water, and a solution of any required strength can be readily made. Taken internally in small doses it does not produce any toxic effect.

Formaldehyde, formyl or formol, is a gaseous body, obtained by the oxidation of methylic alcohol at a moderately high temperature; and, according to Lilly, has the chemical property of uniting with sulphuretted or nitrogenous products of decay, fermentation or decomposition, forming true chemical compounds which are odorless and sterile; and these compounds are in most cases actually antiseptic themselves; hence it is from this property of combining with albuminous or nitrogenous bodies that formaldehyde derives its germicidal and bactericidal powers, since bacteria and micro-organisms generally are not only albumenoid in character, but their food is mainly albumenoid; and when formaldehyde is present, it combines with both the bacteria and their food, thus destroying them, as well as the possibility of their existence.

Medicinal Properties, Etc

The germicidal and antiseptic action of formaldehyde was demonstrated by Low, Aronson, Berlioz and Frillat; also by I. Stahl, who found that formalin is equal in germicidal power to corrosive sublimate, and under certain conditions superior where albuminoid solutions are concerned. In large rooms a 2.5 volume per cent. of formalin in the air destroyed all micro-organisms in a quarter of an hour. When allowed to evaporate in the presence of wool, gauze-bandages, or other dressing material, the vapors of formalin condensed upon the fabrics in solid form (paraformalin) and so disinfected them. Hence dressing materials impregnated with formalin become perfectly sterile, and can immediately be used as antiseptic dressing. The vapor from the spray by a steam atomizer above the patient's head has proven efficient in whooping-cough and chronic bronchitis.

Formaldehyde is relatively non-poisonous, but when brought in contact with the skin, undiluted, causes a tanning effect, making it impermeable, and finally causing necrosis. This action is due to the property formalin possesses of readily penetrating living and dead tissue, and combining with it. Formalin readily and quickly influences both albumin and gelatine, changing them into a tough coagulum which does not lose its form, and possesses persistent antiseptic properties for certain micro-organisms. Formalin attacks only the substance of the contagious material, leaving intact the articles treated, whether of organic or inorganic nature. It is also very readily employed under all circumstances, either in liquid or gaseous form. Its specific gravity closely approximates that of air, hence its power of keeping the atmosphere of an enclosed space uniformly impregnated with formalin vapor. Inhaled in quantity, formalin has marked toxic properties.

Therapeutic Uses

Formaldehyde is a very reliable and useful germicide, antiseptic, and disinfectant. It is non-toxic, active, and permanent, and has no destructive action on vegetable or animal substances when locally applied in the form of formalin. Being of low specific gravity, the vapor of formaldehyde mixes readily with the air, and possesses more penetrating power in loose fabrics than any other germicide. Its activity as a germicide closely approaches, if it does not equal, that of corrosive sublimate. In the strength of 1 to 2,000 it is used in place of the bichloride of mercury for injections in large cavities, etc.

Dental Uses

In dental practice, formalin is employed as an antiseptic and deodorizer in the treatment of putrescent pulps, alveolar abscesses, etc. Also as a local application to ulcers of the mouth, abrasions, etc. One and a half per cent. solutions are used as gargles and mouth washes; also, two and one-half per cent. solutions for ulcers, skin diseases, etc. To make a one per cent. solution, one part of formalin is added to 40 parts of water (1 oz. to 2 1/2 pints). For sterilizing cavities in teeth, a twenty per cent. solution of formalin is very effective, and more especially if the cavity is large, or any decomposed dentine is allowed to remain as a covering to the pulp. It is also serviceable in putrescent canals, and for rendering devitalized pulps hard and leathery after the action of arsenious acid; in such cases a 20 per cent. solution is applied on cotton and permitted to remain for three to six days. For pulp-exposure a 2 per cent solution may be applied before capping. While non-toxic, it requires care in its use, as it is an intense irritant to flesh. A 4 per cent solution will remove putrescent pulp-odor from the fingers.

Paraform, or polymerized formaldehyde, is a colorless crystalline powder, insoluble in water, which when heated gives off formaldehyde gas. This gas is recommended by Dr. H. O. Reik as an excellent sterilizer of instruments, napkins, towels, etc. Paraform pastilles are placed in a small air-tight chamber together with the articles to be sterilized, and formaldehyde gas liberated by means of an alcohol lamp placed underneath.

Glutol is a compound of formaldehyde and gelatin, in the form of a powder, which is antiseptic, and while it dries the surface of wounds and ulcers, seals them and renders them sterile. It is an efficient dressing for burns.