THE DESTRUCTION OF BACTERIA BY CHEMICALS 113 



composed of a union of two molecules of CH 2 O. This is known as a 

 para formaldehyde, and is a white, soapy body, soluble in boiling water 

 and alcohol; it exists in the solution of commerce a clear, watery 

 liquid containing from 33 to 40 per cent, of the gas and 10 to 20 per 

 cent, of methyl-alcohol, its chief impurity. If the commercial solution 

 ordinarily known in the trade as ''formalin" is evaporated or con- 

 centrated above 40 per cent., paraformaldehyde results; and when this 

 is dried in vacua over sulphuric acid a third body trioxymethylene 

 is produced, consisting of three molecules of CH 2 O. This is a white 

 powder, almost soluble in water or alcohol, and giving off a strong odor 

 of formaldehyde. The solid polymers of formaldehyde, when heated, 

 are again reduced to the gaseous condition; ignited, they finally take 

 fire and burn with a blue flame, leaving but little ash. 



Formaldehyde has an active affinity for many organic substances, 

 and forms with some of them definite chemical combinations. It com- 

 bines readily with ammonia to produce a compound called ammoniacal 

 aldehyde, which possesses neither the odor nor the antiseptic properties 

 of formaldehyde. This action is made use of in neutralizing the odor 

 of formaldehyde when it is desired to dispel it rapidly after disinfection. 

 Formaldehyde also forms combinations with certain aniline colors 

 viz., fuchsin and safranin the shades of which are thereby changed 

 or intensified. These are the only colors, however, which are thus 

 affected, and as they are seldom used in dyeing, owing to their liability 

 to fade, this effect is of little practical significance. The most delicate 

 fabrics of silk, wool, cotton, fur, leather, etc., are unaffected in texture 

 or color by formaldehyde. Iron and steel are attacked, after long 

 exposure, by the gas, and more so by its solution; but copper, brass, 

 nickel, zinc, silver, and gilt work are not at all acted upon. Formal- 

 dehyde unites with nitrogenous products of decay fermentation or 

 decomposition forming true chemical compounds, which are odorless 

 and sterile. It is thus a true deodorizer in that it does not replace one 

 odor by another more powerful, but forms new chemical compounds 

 which are odorless. Formaldehyde has a peculiar action upon albumin, 

 which it transforms into an insoluble and indecomposable substance. 

 It renders gelatin insoluble in boiling water and most acids and alkalies. 

 It is from this property of combining chemically with the albuminoids 

 forming the protoplasm of bacteria that formaldehyde is supposed to 

 derive its bactericidal powers. Formaldehyde is an excellent preserva- 

 tive of organic products. It has been proposed to make use of this 

 action for the preservation of meat, milk, and other food products; 

 but, according to Trillat and other investigators, formaldehyde renders 

 these substances indigestible and unfit for food. It has been successively 

 employed as a preservative of pathological and histological specimens. 



There are no exact experiments recorded of the physiological action 

 of formaldehyde on the human subject when taken internally. Slater and 

 Rideal 1 report that a 1 per cent, solution has been taken in considerable 



i Lancet, April 21, 1894. 



