Part IY.] R. S. Pearson: Antiseptic Treatment of Timber . IIS 
(Hi) Mixed Coal Tar Creosote and Petroleum products. 
We have to consider the possibility of mixing a Coal-tar creosote 
with a cheap mineral oil, such as is obtained by rectifying Burma r 
Assam or Persian earth oils, from which Kerosine oil is prepared. Such 
oils are very considerably cheaper than Coal-tar creosotes, so that in the- 
event of the sleepers which have been treated with mixtures of Coal-tar 
creosotes and Petroleum oils proving satisfactory, an important advance 
will have been made in the solution of the problem of treating railway' 
sleepers in India. The functions of mineral oils are to distribute the- 
more toxic oils, to act as a water-proofing agent to the timber and to* 
either reduce the cost of treatment or to allow of more oil being injected 
into the timber. 
(iv) Salt solutions. 
The two salts most commonly used in the impregnation of timber are- 
Chloride of Zinc and Copper Sulphate. Of these, the former has stood 
the test of time, being still used in a few impregnating plants in America 
and, to a still greater extent, on the continent of Europe. Recently, 
soluble fluorides have attracted a Considerable amount of attention in 
America and Austria, while experiments on a laboratory scale have been 
carried out with them in India. Arsenic is another substance which 
has been used, being an ingredient both in the Powell and Atlas processes. 
The reason for not giving pure salts greater attention in India will be 
explained in the next paragraph. 
(v) Mixed impregnation with salt solutions and Coal-tar creo¬ 
sotes combined. 
The last group of antiseptics contain salt solutions such as Chloride of 
Zinc, Sodium Fluoride, Copper Sulphate, Atlas (a patent arsenic solution) 
and a variety of others which, as has been stated elsewhere, are not 
considered suitable for the treatment of timber in localities where moisture 
is in excess, owing to the liability of the salts to be prematurely leached 
out of the timber. This brings us at once to mixed impregnation, first 
with a salt and then with an oil, or to mixing the salt and oil together and 
to treat the timber simultaneously with both preservatives. As a re¬ 
commendation for this method of treatment, it has the great advantage 
that it is cheap as, by treating timber with 10 lbs. per cubic foot of a 
2 per cent, solution of Chloride of Zinc, the cost does not exceed 2 annas 
6 pies per broad gauge sleeper, while the quantity of oil with which it is 
necessary to treat the sleeper amounts to under half that which would 
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