Part VI.] Preparation of Turpentine , Rosin and Gum. 29 
After removing the solvent the steam is let in through the perforated 
coil, and turpentine distilled off at 120°C.-130°C., after which, the steam 
is cut off and the rosin dried by raising the temperature of the steam- 
jacket to about 150°C., when it is run off in a molten state into the rosin 
tank or direct into barrels. 
The residual gum, having absorbed a large quantity of the solvent, 
equal to about its own weight, is subjected to superheated steam, in 
order to recover the solvent. This is done by raising the temperature 
of the still to about 110°C. with the help of the steam jacket while super¬ 
heated steam is passed through the perforated coil at a temperature 
of about 130°C.-140°C. 
The disadvantatge of this method is that the solvent gets unavoid¬ 
ably mixed with the turpentine oil which alters its constants and this, 
though a disadvantage in some respects, does not alter its properties 
as a resin solvent. The reader is referred to page 22, in which he 
will find the analysis of turpentine prepared in bulk by using petro¬ 
leum benzine as a solvent. 
(ii) Steam-distillation followed by solvent extraction. 
The alternative method is to first distil off the turpentine, Ijy passing 
superheated steam at 120°C.-130°C. through the crude material, after 
loading the basket fitted in the solvent extractor, which is kept at a 
temperature of 110°C. with the help of the steam jacket. By this pro¬ 
cess there is no condensation of the water in the still, thus obviating 
absorption of water by the gum. The gum-resin is then treated by the 
solvent, and the solution of rosin run into the settling tank, as already 
described. The gum left in the basket is again treated with superheated 
steam to recover the solvent which it has absorbed after the turpentine 
hp,s been driven off. The advantages of the latter over the former 
process, may be summed up as follows :— 
(1) The oil obtained by the latter process, is free from solvent 
and therefore requires no further rectification. 
(2) The gum and rosin being in a dry state on removal of the 
turpentine, can be easily acted on by the solvent. Any 
moisture contained in the raw material is also driven off 
in the process. 
3) In the latter process, the solution is made up of rosin and 
solvent; in the former case, turpentine is also present. 
To clear the rosin in the latter process requires one heating, 
in the former two heatings, and this is a disadvantage 
* as repeated heating affects the colour of the finished 
product. 
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