254 CHEMICAL DISINFECTANTS AND PRESERVATIVES 



and rust are prevented. Paint affords such a protective 

 covering. The main constituent of paint is a compound of 

 white lead or other nretallic substance; this is mixed with 

 linseed oil or its equivalent in order that it may be spread 

 over wood and metal in a thin, even coating. After the 

 mixture has been applied, it hardens and forms a 'tough skin 

 fairly impervious to weathering. For the sake of ornamenta- 

 tion, various colored pigments are added to the paint and 

 give variety of effect. 



Railroad ties and street paving blocks are ordinarily pro- 

 tected by oil rather than paint. Wood is soaked in creosote 

 oil until it becomes thoroughly saturated with the oily 

 substance. The pores of the wood are thus closed to the 

 entrance of air and moisture, and decay is avoided. Wood 

 treated in this way is very durable. Creosote is poisonous to 

 insects and many small animals, and thus acts as a preserva- 

 tion not only against the elements but against animal life as 

 well. 



