March 16,1872.] 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
745 
a mass of inflammable matter, they are used by the 
natives for candles or torches. Some fine specimens 
of this substance are in the Kew collection. The 
root and herb of Monsonia ovata, Cav., called by the 
Hottentots Keita , are astringent, and are used by 
them in dysentery. 
AN AUTOMATIC THERMO-REGULATOR, TOR USE 
IN THE PREPARATION OF NITROUS OXIDE 
AND OTHER GASES. 
BY FRANK CLOWES, B.SC. LOND. 
The accompanying diagram represents in section a 
modification of the usual air-bath thermo-regulator. 
It was devised to control the source of heat in the pre¬ 
paration of large quantities of nitrous oxide gas for 
anaesthetical purposes. It has been in constant use for 
some time in the laboratory of a distinguished dentist, 
and has. performed its duty perfectly. Its simplicity 
and efficiency will probably recommend its adoption in 
laboratories where large quantities of any gas are pre¬ 
pared, whose rate of evolution is dependent upon the 
amount of heat furnished by a gas-stove or burner. 
S 
The broad jacket AB has a side tube fused in at A, 
and is closed at top and bottom by perforated corks. 
The upper cork bears a long tube 8>H, cut square and 
slightly rounded in the flame at its lower end, which 
descends nearly to the bottom of the jacket; it has a 
small tube fused on at D. To ensure the efficient action 
of the apparatus, the axis of the tube D H must be made 
to coincide with that of the jacket AB. The lower cork 
is traversed by a bent tube, NKB, one of whose ends 
only j us t passes through the cork ; it has a small piece 
joined on at K, on which fits an india-rubber tube carry¬ 
ing at its upper extremity a small reservoir T, which is 
suspended by a wire loop to a peg, and can be raised or 
lowered at will. The side tube at A is joined by india- 
rubber with a T-piece, C, one branch of which is united 
by an india-rubber tube, bearing a screw-clamp, with 
the small side-piece at D, the other branch communi¬ 
cating by gas-tubing with the burner. 
When the apparatus is required for use, mercury is 
poured in at T until it rises sufficiently high in the 
cylinder to close the lower end of the tube HD; the 
supply-tube from the gas-pipes is then fitted on at S, 
the gas passes through IS D W C in the direction indicated 
by the arrows, and is lighted as it issues from the 
burner; the clamp at W is then tightened until the 
amount of gas passing to the burner is just sufficient to 
prevent the flame from being extinguished: the reservoir 
T is lowered, the clamp at X opened, and the mercury- 
level in the jacket allowed to fall considerably below the 
end of the tube SII, so as to give a full supply of gas to 
the burner through SH. As soon as the gas is being gene¬ 
rated in the apparatus at a proper rate, the tube BKN 
is connected at Z by india-rubber with one of the wash- 
bottles of the generating-apparatus, whence the gas pres¬ 
sure acts upon the mercury-level at Y ; the reservoir T 
being raised, the clamp at X is carefully opened, and 
the mercury-level in AB allowed to rise until the gas 
flame just begins to diminish in size ; the clamp is then 
closed. When the pressure of the generated gas in¬ 
creases, it will depress the level at Y, raising the mer¬ 
cury in AB, and diminishing the supply of coal gas, 
and vice versa; the supply of coal gas to the burner 
varying inversely as the pressure in the generating ap¬ 
paratus. It was found unnecessary to use a conical float 
on the mercury, or a slit at Id, as the convex surface of 
the mercury rendered the arrest and renewal of the gas- 
current sufficiently gradual. The apparatus is drawn 
pretty nearly to scale; the diameter of the tubes SDH 
and AC should be about the same as that of the ordinary 
india-rubber gas-tubing, so as not to impede the free 
flow of gas to the burner; the diameter of the little side 
passage D WC may be much less, its object being merely 
to supply sufficient gas to prevent the total extinction of 
the flame by a sudden rise of pressure in the generating 
apparatus; the relative diameters of NYK and AB, 
must depend upon the rise of mercury-level required in 
A B. The apparatus was attached to a flat board and 
suspended upon the wall of the laboratory.— Journ. 
Ckem. Society. 
ESSENTIAL OILS.* 
BY J. H. GLADSTONE, FU.D., F.R.S. 
Part II. 
(Concluded from page 705.) 
Oils containing Oxygen. 
Many of the essential oils consist, as is well known, of 
a body containing oxygen, mixed usually with a hydro¬ 
carbon of the first or second group. This is sometimes 
a product of the direct oxidation of the hydrocarbon, 
and then is generally a feebly acid resin ; but in most 
cases the relation between the two is not apparent. I ew 
of these oils have hitherto been carefully studied. My 
attention has been confined almost exclusively to those 
neutral oils which contain only one atom of oxygen. 
* Read before the Chemical Society, Dec. 7, 1871 (Journ. 
Chem. Soc. [2] x. i,). 
