Preface XXIX. 
to separate benzol or benzine from the alcohol 
to obtain pure or dutiable spirit. In. just the 
same way it is quite impossible to separate 
wood spirit or methyl alcohol from the pure 
spirit by redistilling, as, although the wood 
spirit boils at a lower temperature, they both 
distil over together. In England it is the 
custom to add one-third of 1 per cent. of mineral 
naphtha to the alcohol as a further precaution. 
It would seem, therefore, that a use could be 
found for as much benzol as could be produced 
in denaturing alcohol and rendering it more 
suitable for fuel. The supply of benzol would 
be at least sufficient to cope with the demand 
for the mixed fuel, and it could not be affected 
in a price war, because the cheapness of 
alcohol would be the determining factor, and 
not the price of the comparatively small per- 
centage of benzol. A mixture of pure 100 per 
cent. alcohol with 912 per cent. of 90 per cent. 
benzol gives the best results in practice. 
‘The calorific value of alcohol is little more 
than half the calorific value of petrol by weight, 
but taking volumes into consideration the 
difference is not so marked, because alcohol is 
the heavier fuel. As will be mentioned later, 
experiments have been made which have shown 
that the thermal efficiency of a petrol engine is 
not so high as that of one specially designed 
for using alcohol, and that the net value*per 
unit of volume is not far from the same with 
both fuels. Alcohol, in fact, compares much 
