174 TRANSACTIONS OF ROYAL SCOTTISH ARRORICULTURAL SOCIETY. 



it clear that what is wanted is to form, by means of the creosote, 

 an antiseptic ring in the outer layers of the timber. 



The season of the year at which the timber is cut has an 

 important bearing on the liability to attack by decay-producing 

 fungi. Thus coniferous timber felled and cut up in the autumn 

 is liable to "blueing," which is due to the organism known 

 as Ceratostoma piliferum. Such timber has to be stacked and 

 dried with the greatest care, as it deteriorates rapidly, and 

 does not take creosote well. On the other hand, timber cut 

 in spring or early summer is less susceptible to attack by fungi, 

 and takes creosote much better. 



We have now to consider the composition of creosote. It 

 is a product of the distillation of coal tar, which is, in its turn, 

 an extremely complex mixture of organic compounds, varying 

 in composition not only with different kinds of coal, but even 

 with different treatment of the same coal, according to the 

 amount of heat applied. The creosote oils of commerce come 

 off when the temperature of distillation varies from 435° to 

 520" F., and are heavier than water, the specific gravity varying, 

 but being about I'oyo. Creosote oil contains napthalene and 

 other solids which, however, tend to form a sediment, and can 

 only be introduced into the timber when in solution. In this 

 country such solids are usually removed from commercial 

 creosote in the process of manufacture, but in some parts of the 

 Continent, where the pressure method of impregnation is 

 adopted, this is not done. This fact has an important bearing 

 upon methods. As on the Continent a viscous, solid-containing 

 oil is employed, it is considered advisable to heat the creosote 

 by means of a spirally-arranged steam pipe within the operating 

 cylinder. This method is not usually adopted here, on account 

 of the fact that the oil employed is thinner, and has had most 

 of its solids removed. Any remaining solids are most con- 

 spicuous in cold and frosty weather, which also increases 

 the viscosity of the oil and retards the impregnating process. 

 The composition of the commercial oil varies greatly, and there 

 are associated differences in colour, physical properties, and 

 effects upon timber. The following table shows the results of 

 analyses of three separate samples of oil, withdrawn from the 

 overflow pipes of the cylinder in use at some large works. 

 These analyses have been kindly supplied by a friend of the 

 writer's. 



