FORMALIN, or FORMALDEHYDE, CH2O

This article appears in Volume V10, Page 667 of the Encyclopedia Britannica.

Encyclopedia Britannica - Main :: FLA-FRA

FORMALIN, or FORMALDEHYDE, CH2O or HCHO, the first member of the

series

SERIES (a Latin word from serere, to join)

of saturated aliphatic aldehydes. It is most readily prepared by passing the vapour of methyl alcohol, mixed with air, over heated copper or

platinum

PLATINUM [symbol Pt, atomic weight 145.0 (0=16)]

. In order to collect the formaldehyde, the vapour is condensed and absorbed, either in water or alcohol. It may also be obtained, although only in small quantities, by the

distillation

DISTILLATION (from the Lat. distillare, more correctly destillare, to drop or trickle down)

calcium

CALCIUM [symbol Ca, atomic weight 40.0 (o= x6)]

formate, At

ordinary

ORDINARY (med. Lat. ordinarius, Fr. ordinaire)

temperatures formaldehyde is a gas possessing a pungent smell; it is a strong antiseptic and disinfectant, a 40% solution of the aldehyde in water or methyl alcohol, sold as formalin, being employed as a deodorant, fungicide and preservative. It is not possible to obtain the aldehyde in a pure

condition

CONDITION (Lat. condicio, from condicere, to agree upon, arrange; not connected with conditio, from condere, conditum, to put together)

, since it readily polymerizes. It is a strong reducing agent; it combines with ammonia to form hexamethylene tetramine, (CH2)6N4, and easily " condenses " in the presence of many bases to produce compounds which apparently belong to the sugars (q.v.). It renders glue or gelatin insoluble in water, and is used in the coal-tar colour industry in the manufacture of para-rosaniline, pyronines and rosamines. Several polymers have been described. Para formaldehyde, or trioxymethylene, obtained by concentrating solutions of form-aldehyde in vacuo, is a white crystalline solid, which sublimes at about too C. and melts at a somewhat higher temperature, changing back into the

original

ORIGINAL

form. It is insoluble in cold water, alcohol and ether. A diformaldehyde is supposed to

separate

SEPARATE

as white flakes when the vapour is passed into chloroform (Korber, Pharm. Zeit., 1904, xlix. p. 609); F. Auerbach and H. Barschall (Chem. Zentr., 1907, H. p. 1734) obtained three polymers by acting with concentrated sulphuric acid on solutions of formaldehyde, and a fourth by

heating

HEATING

one of the forms so obtained. The strength of solutions of formaldehyde may be ascertained by the addition of excess of standard ammonia to the aldehyde solution (hexamethylene tetramine being formed), the excess of ammonia being then estimated by titration with standard acid. On the formation of formaldehyde by the oxidation of methane at high temperatures, see W. A. Bone (Journ. Chem. Soc.,' 1902, 81, p. 535; 1903, 83, p. 1074). Form-aldehyde also appears to be a reduction product of carbon dioxide (see Annual Reports of the Chemical Society).

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