282 PROCEEDINGS of THE 



of the shortlived woods conform to the requirements 

 for long increase in length of life, just referred to, and 

 that it will pay to use them. 



Having decided upon the timber available which 

 can be treated, the next problem is, how shall the 

 timber be treated ? In other words, what method shall 

 be used? There are a host of processes, beginning 

 with the metallic salts, like copper, zinc, mercury, etc., 

 and ending with creosote or tar oil, either alone or 

 in combination, for all of which certain merits are 

 claimed, omitting, for the present, processes employing 

 chemicals of unknown preservative value. I will not , 

 have the time to discuss this important question at any 

 length and will restrict my remarks to a few general 

 considerations which it seems to me should govern in 

 the choice of a preserving process. 



I regard the choice of a process entirely as one 

 involving a certain risk in investment. One must 

 start, of course, with the assumption that any one of 

 half a dozen processes under consideration will actually 

 preserve the wood for a shorter or longer time. This 

 assumption is not unfair, when one is dealing with 

 preservatives of such known value as zinc chloride, 

 copper sulphate, mercuric chloride, creosote or tar oil, 

 and possibly one or two others. Assuming, then, that 

 these preserve wood, one naturally comes to the 

 question of cost. This one may regard from two 

 standpoints; the first one, which is the usual one in 

 Europe, considers the annual charge; in other words, 

 the saving which can be made in the long run when 

 comparing an untreated with a treated piece of wood. 

 A glance at the table which I presented a few moments 

 ago will show that in the long run the creosoting 

 process in some form is the cheapest, even if it costs 

 more at the beginning ; in other words, the annual 



