STERILIZATION AND DISINFECTION 75- 



less value in disinfecting barns, stables and the like than in 

 houses. The gas must be liberated rapidly in large quantities 

 and there should be moisture present. Formaldehyde is used 

 as a spray in the strength of 1 part of formalin to 10 of water. 

 It is, however, more usually employed in the gaseous state. 

 Formaldehyde gas may be obtained in the following ways. 

 (1) By heating formalin (40 per cent aqueous solution of 

 formaldehyde) in an autoclave under pressure or (2) in a 

 retort without pressure (3) By adding formalin to potassium 

 permanganate and (4) By heating paraform. In producing 

 formaldehyde gas for disinfection purposes a large volume of 

 gas should be evolved in a very short time. There are on the 

 market several forms of apparatus for generating formalde- 

 hyde gas. Formaldehyde gas may be generated from a lamp 

 by a dehydrogenation of the vapor of wood alcohol in passing 

 it mixed with air over incandescent platinum. The following- 

 reaction takes place. 



CH 3 OH H- O = HCOH + H 2 O 

 methyl alcohol oxygen formaldehyde water. 



Formaldehyde is more commonly used as a disinfectant 

 by liberating it from solid forms into which it can be con- 

 densed. The gas is a complex unstable body and failures in 

 its use as a disinfectant are attributable to an imperfect 

 knowledge of its properties and methods of production. 



Formaldehyde (HCOH) exists in at least three isomerie 

 states ; (1) formic aldehyde is a gas at ordinary temperatures, 

 colorless and possessing a slight odor and having a very irri- 

 tating effect upon the mucous membranes especially those of 

 the nose and conjunctiva. At a temperature of about 20 C. 

 the gas polymerizes into paraformaldehyde which is known 

 commercially as paraform, (2) Paraform is a white substance 

 soluble in both water and alcohol. It consists chemically of 

 two molecules of formaldehyde. It is this substance which it 

 is supposed constitutes the commercial solutions of formalde- 

 hyde known as formalin, formol, etc. (3) Trioxymethylene is 

 formed by the union of three molecules of formaldehyde. It 

 is a white powder giving off a strong odor of the gas. It is 



