350 — Liquefaction and Solidification of Carbonic Acid. 
at J; so that when the receiver is being separated from the gen- 
erator, the contents of both may be retained. The stop-cocks in 
common use are inadequate to resist the pressure, and therefore a 
‘screw stop-cock is indispensable. - It is made to close a small 
aperture by means of a conical point, and having a double cone, 
it closes an outlet also when the cock is completely open, so as 
to prevent the escape of gas by the sides of. the screw. 
The receiver, F, is of the capacity of about.a pint. The pipe, 
G, G, turned at a right angle at G, descends so as almost to touch 
the bottom of the cavity in F. The’ stop-cock H, G, is similar 
tolandJ. L isa glass tube connected at each end to a socket 
of brass, which communicates with the interior of F. It is the 
gauge for observing the level of the liquid in ¥. > 
The gauge for measuring the pressure is pec culiar.. Into a 
wrought iron box, S, are inserted, by screws, two soekett T and 
U. The former descends almost to the bottom of the box, which . 
is nearly filled with mercury. Through the axis of the screw, 
X, a small tube passes into the cavity of S, and is continued to 
the top of it, so as to risé above the mercury. ‘Two strong ba- 
ab s, R and M, are cemented* into U and W, and her- 
eal ed at the upper ends. These tubes are carefully 
In one of them, U, a-short cylinder of mercury is 
made to stand at Y at the commencement of the experiment. 
The other, socket and all, is full of air, as no mercury is intro- 
duced into it. A very fine screw at W, enables the operator to 
The tin cup, O, used to collet the solid acid, is covered by a 
lid, Z, perforated oF a pipe, P, whose top is full of small holes. 
The hearslle Q, is hollow, so as to fit the end of the pipe of the 
receiver at G. To secure the hand of the operator from the cold 
produced by the experiment, the handle is rae wrapped up 
in some kind of cloth. - 
The apparatus is _prepared for use -by removing ‘the screw E, 
and placing 8 Ibs. of bicarbonate of soda in the generator, A, 
* The cement used was made of shell lac 3 or 4 parts, white or crude pa a 
tine 1 part, melted at as low a temperature as possible, so as not to make bu 
in the mixture. This cement is very strong, but liable, without great care in the 
regulation of the heat, to have capillary tubes in it from the vaporization of the. 
niine. This defect may be completely = by cutting away, when 
cold, the external mass of cement, and putting on a little common cap cement, 
which melts at a much lower setintianess sad Deaae ¢ the tu 
