DESTRUCTION OF BACTERIA BY CHEMICALS. 161 
The methyl-alcohol is oxidized and produces formal- 
dehyde as follows: 
CH,OH + 0 = CH,O — H,0. 
Formaldehyde is a gaseous compound having the 
chemical formula CH,O and possessed of an extremely 
irritating odor. At a temperature of 68° F. the gas 
is polymerized—that is to say, a second body is formed, 
composed of a union of two molecules of CH,O. This 
is known as a paraformaldehyde, and is a white, soapy 
body, soluble in boiling water and alcohol; it exists in 
the solution of commerce—a clear, watery liquid con- 
taining 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 concentrated above 40 
per cent., paraformaldehyde results; and when this is 
dried in vaccuo over sulphuric acid a third body— 
trioxymethylene—is produced, consisting of three mole- 
cules of CH,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 condi- 
tion; 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 chem- 
ical combinations. It combines 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. Formal- 
11 
