■ON OIL OF TURPENTINE. 
225 
very little inferior to caoutchouc. This is now the solvent 
for caoutchouc, employed both in France and England, for 
the manufacture of impermeable textures. What change 
has this process effected in the turpentine? Does it form 
new volatile products, or is it simply a modification of the 
molecular constitution of the oil? We can now answer 
these questions. 
The physical properties of the oil distilled on brick are as 
follow: — The eolour is slightly yellow^ its odour that of a 
mixture of thyme, naptha, and turpentine. It is more lim- 
pid than the essence from which it is formed, the density 
of the former being, 0.8736, and after distillation, 0.8420. 
It begins to boil at 85° C, but the temperature immediately 
rises to 154°, and remains at this point nearly stationary. 
I have tried to isolate the more volatile part of the distillate, 
but without success. The unchanged oil boils at 151° to 
158°, whilst the distilled boils at 150°. I analysed the 
modified oil, and found its composition precisely the same 
as the original. The nature of the modification in question 
being still obscure, during the last winter I employed the 
apparatus for polarization belonging to the Hotel Dieu, to 
pursue the inquiry, and I found that by its means I was 
able to perceive the molecular change which the turpentine 
had undergone in becoming able to dissolve the caout- 
chouc. 
Commercial oil of turpentine, acting imperfectly upon 
caoutchouc, has a molecular rotation of — 2S°,83. After 
distillation over a naked fire, this became — 33°,23; its 
power of dissolving caoutchouc increasing with its power 
of molecular rotation. If the same essence, however, is 
modified by a temperature still more elevated, as by distil- 
ling it on fragments of brick, its solvent power increases still 
further, but the change produced is accompanied by a con- 
siderable diminution in its rotatory power, which is then 
only — 8,68. 
20* 
