RELATION TO ENVIRONMENT 149 



the market as a solution. In its ordinary form the watery 

 solution contains 40 per cent of the gas. For purposes of dis- 

 infection formaldehyde maybe used either as a gas or a solution. 

 Its uses as a gas will be considered first. 



The gas may be produced in the space to be disinfected 

 directly from the methyl alcohol, and for this purpose a number 

 of special lamps have been manufactured. The cheaper ones 

 are unsatisfactory in that they are likely to give an uneven 

 product ; the more expensive ones may be quite satisfactory, 

 but both have the disadvantages of leaving a fire burning in a 

 closed room, which is liable to lead to accidents, so that the 

 gas is almost uniformly produced at the present time by 

 regenerating it from the solution. It might naturally be 

 expected that this would be a simple matter, and that all 

 that would be necessary to do would be to evaporate the 

 solution, but when formaldehyde solution evaporates under 

 ordinary conditions it is likely to polymerize; that is, two or 

 more molecules unite to form a very different substance. 

 Some of the polymers, in this case, are solid, so that if an 

 ordinary pan of formaldehyde is evaporated a considerable 

 amount of a white solid is formed, known as paraformaldehyde. 

 In this case the formaldehyde, instead of being given off as a 

 gas, goes into this polymerized form and is lost as a disinfectant. 

 The danger of polymerization is overcome in several ways ; 

 one of the means that has been most widely used is the rapid 

 heating of the solution, above the boiling point, in an autoclave, 

 or in special retorts. It has also been found that if glycerine 



