SENILISING. 309 



ible. For superficial coating, oil-paint can be made non- 

 inflammable by adding phosphate of ammonia and borax in the 

 form of impalpable powders ; while asbestos paint and mortar 

 made of plaster and asbestos are also used, and give partial 

 security against fire. Of several methods of fireproofing wood 

 by impregnation under strong pressure (though unfortunately 

 always only to a limited depth), Payne's process is one of the 

 best, the wood being first impregnated in a vacuum with a strong 

 sulphate of iron solution, then under pressure injected with a 

 solution of sulphate of lime or some alkaline carbonate to make 

 the iron insoluble. 



Electricity is also used in France, both to " senilise " wood 

 rapidly in order to make it more durable, and to fireproof it. 

 Senilising takes place by impregnating green wood with a 20- 

 per-cent solution of magnesium sulphate warmed to about 90 F., 

 passed in for seven to fourteen hours by an electric current 

 varying from 4 to 6 amperes, and then drying it in the open air ; 

 while for fireproofing, ammoniacal salts are used in place of 

 magnesium sulphate. And in another French process of senilis- 

 ing, a solution of 10 per cent borax and 5 per cent resin-soap is 

 used in place of the 20-per-cent solution of magnesium sulphate. 

 But as yet it is too early to judge of the success of these 

 methods. 



