306 
SELECTED ARTICLES. 
U and W 5 and hermetically sealed at the upper ends. These 
tubes are carefully graduated. In one of them, U, a short 
cylinder of mercury is made to stand at Y at the commence- 
ment of the experiment. The other, socket and all, is full 
of air, as no mercury is introduced into it. A very fine 
screw at W, enables the operator to regulate the quantity of 
air in T. 
The tin cup, 0, used to collect the solid acid, is covered by 
a lid, Z, perforated by a pipe, P, whose top is full of small 
holes. The handle, 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 
carefully wrapped up in some kind of cloth. 
The apparatus is prepared for use by removing the screw, 
E, and placing 1| lbs. of bicarbonate of soda in the generator, 
A, to which 24 fluid ounces of water are to be added. After 
making these into a thin paste by stirring, nine fluid ounces of 
common sulphuric acid are to be poured into the copper cup, 
N, and that is to be let down by a crook of wire into the 
generator. After the screw, E, has been firmly applied, and 
the stop-cock, J, closed, the contents of the generator are to 
be brought into admixture by moving it round to a horizontal 
position on the swivel, D, which is supported by the wooden 
frame, B, B. There is a check-bar at C. This motion is to 
be repeated several times. In about ten minutes the whole 
of the carbonic acid is liberated, and exists in A, chiefly in a 
liquid state. 
The next step in the process is to attach by means of the 
stirrup and screw, K, K, the receiver, F, previously cooled 
by ice. The keys, I and J, may then be opened slowly, and 
instantly the liquid carbonic acid is perceptible in the gauge, 
make bubbles 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 turpentine. This defect may be com- 
pletely corrected by cutting away, when cold, the external mass of cement, 
and putting on a little common cap cement which melts at a much lower 
temperature and closes the tubes. 
