402 On a volatile concrete Oil 
however the heat, they rise in a visible odorous vapour, and the 
paper becomes opaque without retaining any trace of unetuosity. 
Moreover, this oily. spot entirely disappears from the paper by 
the action of the solar rays, and even by the mere temperature 
of the atmosphere. By the !atter mode the spot did not vanish 
till after twenty-eight days, during which the thermometer of 
Reaumur did not indicate a temperature above 14°. 
6th. Liquefied and absorbed by a cotton thread, they inflame 
when brought into contact with the flame of a canille. 
7th. Spread and pressed on paper coloured with turnsole, the 
paper reddens very sensibly. 
Lastly. The solution of sulphat of iron neither makes them 
become violet nor black. 
These properties, however, sufficiently prove that this sub- 
stance isa volatile concrete oil, and consequently cannot be con= 
founded with gallic acid. Nor does the circumstance of its red- 
dening the paper containing tincture of turnsole furnish any 
objection, as M. Vogel asserts that he has found no volatile oil, 
however recent, which wants the property of changing to red 
this tincture *. 
__ The liquid from which this oil was separated by filtration, had, 
like what is called aromatic water, the same taste and smell as. 
the oil itself. It did not change to violet or black the solution 
of sulphate of iron,—hence, did not contain gallic acid; and it 
gave a slight tinge of red to the blue of turnsole. This redden= 
ing was owing perhaps to the acetic acid, which is found free in 
galls, and passes over with the water in the distillation, as Bouil- 
lon Lagrange has shown f. 
The galls from which I extracted the above-mentioned volatile 
oil are small, heavy, of a reddish-yellow or orange colour, more 
or less tending te dark or to blackish, wrinkled externally with 
some protuberances, and not spongy internally. The next ob- 
ject was to know if the same oil existed in the nut-galls of the 
oak in general; and with this view I procured galls of different 
qualities which are distinguished by the following appellations : 
Htalian or Tuscan galls, Istria galls, yellowish and black, Alep- 
po or Smyrna galls. 
Wishing that the experiments about to be performed should 
he comparative, I distilled separately six ounces of the above- 
mentioned kinds of galls with eight ounces of water {, in a glass 
retort placed almost superficially on a sand-bath, the mouth of 
Which touched the bottom of a small receiver which I had united 
* Journal de Physique, \xxx. 256. + Annales de‘Chimie, ¥x..173-5. _ 
{ The same quantity and quality of galls do not absorb an equal dese of 
water, so that in the above cight ounces there was more or less supenabux- 
dant. 
to 
