SEASONING AND IMPKEGNATION OF TIMBER 287 



extra for artificially treating them, or use more costly but 

 harder and more durable timber which will not need 

 artificial treatment, or again, in cases where a long life is 

 not required, use the softer timber in its natural state. 1 



Fireproof Timber. Many experiments have been made in 

 the direction of rendering the timber fireproof, but not 

 much practical result has been attained, and so called fire- 

 proof timber has been but little used. Practical experience 

 has narrowed the efficacious compounds to be used in the 

 fireproof treatment of timber to ammonium chloride, 

 ammonium phosphate, ammonium sulphate, calcium 

 chloride, alum, borax, boracic acid, and a few others. 



The solutions, which are said to penetrate right into the 

 interior of the wood, do not affect the workmen's tools, and 

 the treated timber will take paint, stains, varnish, etc., just 

 as well as untreated wood. 



According to Professor Vivian B. Lewis, they crystallise 

 in the cells of the wood, and under the influence of heat 

 " the ammonium phosphate decomposes to ammonia gas 

 and phosphoric acid, the former driving all air out of the 

 cells and replacing it by a non-inflammable gas, whilst the 

 phosphoric and boracic acids fuse and coat the cell walls 

 with a glaze which, while allowing the gases from the 

 decomposing cellulose to escape, prevents the access of 

 oxygen from the air to carry on further combustion." 



1 In 1901 there were only fifteen timber treating plants in the 

 United States; in the following six years this number was increased to 

 fifty. 



