Part IV.] R. S. Pearson: Antiseptic Treatment of Timber . 19 
each year’s treatment to be different. As the work progressed from 
year to year, the numbers of sleepers treated had to be modified and 
finally 7,980 sleepers in all were handed over to the State Railways. 
(ii) Selection of species. 
The first point to be decided upon was the selection of the species of 
timber with which to carry out the experiments. Some difference of 
opinion was experienced as to which species should be selected, it being 
essential that (i) the species be available in large quantities, (ii) the cost of 
extraction should not be excessive, (Hi) the timber be mechanically strong 
enough to withstand the wear and tear to which it would be subjected, 
and (iv) the timber should lend itself to treatment. It was finally decided 
to subject five species of timber to trial : namely, those of Dipterocarpus 
tuberculatus, D. alatus, Pinus longifolia, P. excelsa and Terminalia 
tomentosa, and it is with these five species that all the Open Tank 
experiments have been carried out. 
3. Antiseptics used. 
In connection with the choice of antiseptics it was necessary to con¬ 
sider, (i) which solution would probably render the timber most durable 
and* (ii) the cost. When settling the first point, the results obtained 
from the laboratory experiments were naturally taken into consideration, 
as also the mass of literature available on the subject from Europe and 
America. In preference to salt solutions, everything pointed to the use 
of high boiling-point oils in a country like India, where the temperature 
during a portion of the year is very high and the moisture during the mon¬ 
soon period is excessive. Were durability the only factor to be considered, 
it would not have been necessary to consider experimenting with other 
antiseptics. Cost, however, claims nearly equal attention, so that it 
was decided to experiment also with combined salt and oil solutions. 
Further, as at that time the Powell process was being much discussed, 
it also called for consideration. It was finally decided to experiment 
with (i) the Powell process, (ii) with Avenarius Carbolineum oil, (Hi) 
with a mixed impregnation of Chloride of zinc , the salt being protected 
by a coating of Green oil, and (iv) with a mixture of Solignum and 
Rangoon oil or Liquid Fuel . 
4. Method of Treatment. 
The relative merits of the Open Tank treatment as opposed to Pressure 
plants will be discussed hereafter. In the case of these experiments 
everything pointed to the use of Open Tanks, for the reason that little 
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