82 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 
The composition and consequent weight of coal-tar, and of the 
dead oils made from it, vary not only with the quality of the coal 
from which the gas is manufactured, but also with the temperature 
at which it is carbonised. Dr Tidy’s specification does not fix any 
specific gravity for creosote, but it is found that oils having specific 
gravities of 1040 to 1060 (water being taken as 1000) give the 
best results, though in some creosoting works heavy and light oils, 
and even shale oils, are used indiscriminately. 
The volatile nature of the lighter oils is clearly shown by the 
result of some experiments made at the railway works at Inchicore, 
Dublin, in 1885, by Mr J. A. F. Aspinall, M. Inst.C.E., and 
communicated to the Institution of Civil Engineers of Ireland in 
1886. Mr Aspinall selected sixteen dried sleepers, each 9 feet by 
10 inches by 5 inches, to be creosoted with heavy oil of 1055 
specific gravity, and sixteen similar sleepers to be creosoted with 
light oil of 974 specific gravity. When creosoted, the thirty-two 
sleepers were carefully wiped clean of superfluous oil, weighed, and 
laid flat on skids on the ground, exposed to the weather. At the 
end of seven months they were immersed in a large tank of pure 
water for four weeks, care being taken to keep them below the sur- 
face, and the water being changed once a week. They were finally 
placed on end, exposed to sun and rain, for a further period of 
four weeks. The sleepers creosoted with heavy oil absorbed 8°77 
lbs. per cubic foot, or 27-4 lbs. per sleeper; and those creosoted 
with light oil absorbed 10°26 lbs. per cubie foot, or 32 lbs. per 
sleeper. The final result, two months after immersion, was that while 
only 0:25 lb. per sleeper of the heavy oil was lost, 2 lbs. per sleeper 
of the light oil had disappeared, either washed out or evaporated. 
As usually practised in Britain, the process of creosoting is as 
follows:—The timber to be treated is placed in a cylinder or 
receiver constructed of iron or steel plates riveted together, and 
resembling in appearance a steam boiler. In large establishments, 
where railway sleepers, telegraph poles, or heavy timbers are 
creosoted, these receivers are from 50 to 60 feet long, and 6 feet 
or so in diameter. One or both ends of the receiver are made 
movable, for the purpose of inserting and withdrawing the timber. 
Where large quantities of timber have to be handled, this is most 
conveniently done by stacking it in the open on small, low-wheeled 
bogies, which are run into the receiver on rails laid on its floor, 
and though the capacity of the receiver is considerably lessened by 
the space occupied by the bogies, it is found that the facility with 
