THE PRESERVING OF TIMBER FOR ESTATE PURPOSES. 81 
as they contain the largest proportion of these acids, while the 
naphthaline was considered to be of little value, and was excluded 
as far as possible. 
Further investigation, however, has not confirmed this view, but 
has shown that carbolic acid, being very volatile, soon evaporates, 
and that the best results are obtained with creosotes containing a 
considerable preportion of naphthaline and other semi-solid con- 
stituents, which do not distil over except at the higher 
temperatures ; and the later specifications for creosoting generally 
give effect to this view. 
Dr O. Meymott Tidy, the well-known chemist, speaking at the 
Institution of Civil Engineers, London, in 1884, said that he 
considered the process of creosoting to be of a three-fold nature: 
(1) a physiological action rendering the wood a poison, so that 
animals would not attack it; (2) a chemical action, consisting 
chiefly in the coagulation of the albumen; and (3) the simple 
mechanical action, practically choking up the pores of the wood, 
so that neither air, moisture, nor life could get inside, and this 
he held to be by far the most important action of the three. 
He considered that it was highly advisable to get the heaviest 
creosote for the work, and that the excellence of the creosote 
should be determined by the amount of those oils which did not 
distil over at a temperature of 600° Fahrenheit; but on the other 
hand, having examined a very large number of creosoted timbers 
that had been prepared for at least a year, he was unable to detect 
the slightest trace of carbolic acid in them. With these views he 
had framed a specification for creosote, which had been largely 
adopted, and in which, while providing for a large proportion of 
the heavier constituents of the oils, he had fixed the quantity of 
carbolic acid as low as was consistent with obtaining a genuine 
crecsote, 
Summarised, Dr Tidy’s specification provides,— 
1. That the creosote shall be completely liquid at a tempera- 
ture of 100° Fahrenheit, and that no deposit shall take 
place until the temperature of the oil falls to 93° 
Fahrenheit. 
2. That the creosote shall contain at least 25 per cent. of 
constituents that do not distil over at a temperature of 
600° Fahrenheit. 
3. That the creosote, when tested by the caustic-soda process, 
shall yield a total of 8 per cent. of tar acids. 
VOL. XIV. PART IL, F 
