76 
SELECTED ARTICLES. 
place, when dry substances are operated on, which ought to 
be submitted to previous maceration; and, finally, to increase 
the temperature of the water, and thus facilitate the extrication 
of a large proportion of essential oil. This last effect, so in 
accordance with theory, has led me to doubt the exactitude ot 
the result announced by M. Mialhe, and I have, in fact, found, 
contrary to his opinion, that upon comparasion with distilled 
water alone, and salt water, more oil is obtained in the second 
case than the first. 
I made the trial in a copper alembic, and in order to avoid 
as much as possible all condensation of vapor in the capital, I 
enveloped it with woollen cloth, as far as the insertion of the 
worm of the apparatus. I placed in the alembic distilled 
water with the rectified essence of turpentine, which covered 
it w r ith a layer three or four inches inches in thickness, and I 
commenced to collect the products only when the distillation 
was in full activity, the apparatus being sufficiently heated. 
Now, during the whole time that the distillation was in pro- 
gress, the water and the essential oil which were condensed 
in the recipient, were always in the proportion of 1 to 0.757 
in volume, or 1 to 0.66 in weight. These are precisely 
the relative quantities that should result from the con- 
densation of a saturated mixture of the vapor of water and 
that of turpentine, at the temperature of 100 degrees, and 
under a pressure of 76 c, estimating from the tension proper 
to each of the vapors. 
This relation continued so long as the oil covered the sur- 
face of the water with a uniform layer; when the quantity 
diminished so as only to cover the water with large globules, 
an excess of the vapor of water passed over, and the propor- 
tion of the oil was observed to diminish more and more in 
the product. 
I made another experiment by adding to water half its 
weight of salt. Upon this occasion the relation was com- 
pletely changed. Water being taken as unity in volume, 
that of the oil was 1.75; the relation in weight was as 1 to 
1.517. Thus theory and experiment coincided. The pre- 
