60 PROTECTION OF PLATSTS, 1920-21 



In order to arrive at a clear idea of the economy, or otherwise, of treatment, 

 the above items of expense will have to be added togethet, and the total divided 

 by the number o;f years that a post treated with antiseptic will last, and again 

 by the number of years that an u'ntreated post lasts, and so at last the cost per 

 post per year is known. If ordinary material, needing treatment before using as 

 posts, is employed, the initial expense is less, because time and effort have not 

 been expended in searching for any special kind of wood. The cost of transport 

 should also be small in such a case, i. e., if any ordinary wood,foundin abund- 

 ance on practically^ every farm, is used. The cost of removing the bark and of 

 seasoning will be higher, for it is necessary that the wood be carefully seasoned 

 and the bark thoroughly removed, before it is used. 



The cost of treatment is the most important item, and this will depend on 

 the particular preservative and on the method by which it is applied. If the 

 farmer uses only treated posts, then the annual charge for maintenance will 

 be much less, as the posts last so much longer. A po'int that must not be for- 

 gotten is that the period of treatment for the wood must be quite short. 



Choice of a preservative 



Experience has shown that creosote, or anything prepared from oil of tar, 

 is the best preservative for wood that is to be used in wet places, and this for 

 two reasons : (1) Creosote is a chemical poison for the different fungi which 

 bring about the decay of the wood and also for the numerous insects which des- 

 troy it ; and (2) Creosote is a heavy oil, insoluble in water. If the wood is 

 thoroughly saturated with creosote, it will take up only very little Avater. As 

 moisture and air are necessary for the growth of fungi, wood treated in this way 

 will remain sound for an indefinite period. 



Other substances can also be employed siich as Chloride of Mercury, or of 

 Zinc, or even Sulphate of Copper, or one of many other compounds which are 

 veritable poisons foV fungi and insects, but these are all solu^ble in water and 

 would be dissolved out when the post was established in a damp soil. The 

 wood would then be exposed to attack by agents of destruction. 



Creosote is an oily product obtained in the manufacture of coal gas, and is 

 a substance more or less variable in quality. The heavier or more dense the oil 

 that is used, the slower does it penetrate into the wood under treatment ; but 

 such oil does not evaporate readily either during treatment or after. If a 

 lighter liquid is used, penetration takes place re9,dily, but evaporation is also 

 fairly rapid. 



Creosote can be obtained in most towns where coal gas is made. In Can- 

 ada, in 1915, the price varied from ten to twenty-five cents a gallon, and has 

 not advanced much to-day. The rather wide variation in price already men- 

 tioned depends on the quality, the specific gravity, the quantity purchased 

 and, finally, the cost of transport. 



