— 86 — 
in the first place he allows lo cc of the turpentine oil to be examined, 
to drop slowly and at slightly reduced temperature into 40 cc con- 
centrated sulphuric acid. After 10 to 12 hours 8 to 9^/^ of the turpentine 
oil used separate off. Now the lower dark-brown layer is allowed to 
drain off, and the remaining oil is once more shaken with 3 to 4 cc 
fuming sulphuric acid. After standing for several hours, a further 
I to 2 of the oil separate off, whilst if mineral oil is present the 
volume is proportionately larger. 
M. Vezes^) has published a work dealing with the examination 
of French oil of turpentine. He considers it useful in the examination to 
distinguish between normal adulterants such as resin oil and colophonium, 
which may enter into the turpentine oil during the manufacture, and 
abnormal adulterants, such as petroleum, benzine, etc., w^hich are only 
subsequently added to the oil. The method tested by Vezes resembles 
that recommended by Zune^) for testing for resin oil. 
250 cc turpentine oil are divided by fractional distillation into 
five portions of 50 cc each, of which four are distillates, whilst the 
distillation-residue represents the fifth. Having regard to the fact that 
the boiling points of the adulterants differ from that of turpentine oil 
(152° to 160°), the middle fraction 3 can be regarded as pure oil, 
whilst the adulterants must be found in the extreme fractions. For this 
reason Vezes determines under the identical physical conditions the 
indices of refraction n, ng and n5 of the fractions i, 3, and 5, and 
judges the purity of the oil from the differences of the values found, 
of which he designates ng — n^ as d, and — Ug as Zl. By a systematic 
study of d and A in mixtures of rectified turpentine oil with the adulterants 
possible in practice, he arrives at the conclusion that, when normal 
adulterants are exclusively employed, d remains fairly constant (as in 
the case of rectified oil 0,0000 d <^ 0,00 1 o), whilst A increases with 
the percentage X of the admixture. The experiments showed A = 
0,003 2 -|- 0,003 7 X- From this formula the entire quantity of normal 
adulterants can be calculated; by determining the acid number A the 
A 
percentage of colophonium is found from the equation C = — so that 
from the difference X — C the percentage of resin oil is ascertained. 
The addition of abnormal adulterants possible in practice is made specially 
conspicuous by a lowering of the boiling point, and by the considerable 
alteration in the differences d and A. Vezes requires for a good 
commercial oil : 
') Bull. soc. chim. III. 29 (1903), 896. 
^) Compt. rend. 114 (1892), 490. — Gildemeister and Hoffmann, "The 
Volatile Oils" p. 237. 
