LIQUEFACTION AND SOLIDIFICATION OF AIR AND HYDROGEN. 161 
containing liquid carbonic acid, compressed by tbe pumps, 
and surrounded by liquid sulphurous acid, contained in a tube 
5 inches in diameter and 3 feet 7 inches long. 
(h) A non-conductor of heat, with a wooden covering. 
(k) A tubular condenser for liquid sulphurous acid, com- 
pressed by the pumps. 
(p) Double-action exhaustion and force pumps; two for 
drawing carbonic acid either from the tubular condenser or 
from the gas-holder, according to the position of a three-way 
cock ; the other pair for exhausting sulphurous acid from the 
tube surrounding d. 
The following is a concise description of the working of the 
apparatus : — A pair of pumps such as are used in the freezing- 
machine are so coupled that the exhaustion of one corresponds to 
the compression of the other. The exhaustion of the first pump 
communicates with the tube enclosed in (h), which contains liquid 
sulphurous acid. Under the influence of a good vacuum the 
temperature of this liquid rapidly sinks to —65° C. ( — 85° F.), 
or even to —73° ( — 100° F.), the lowest limit attained. 
Through this tube of sulphurous acid passes a second smaller 
one, in which is retained compressed carbonic acid. The car- 
bonic acid, made from hydrochloric acid and Carrara marble, is 
washed and dried and stored over oil in a gas-holder. 
At a pressure of six atmospheres the carbonic acid liquefies 
under these circumstances. The resulting liquid is passed into 
the long copper tube (c) (fig. 4). 
A pair of pumps are arranged to exhaust carbonic acid either 
from this tube (c), or from the gas-holder (g). When the car- 
bonic acid vapour is extracted from the tube in which it is 
contained the liquid solidifies, and its temperature descends to 
— 140° C. ( — 220° F.). The subtraction of heat is maintained 
by the working of the pumps, the cylinders of which extract 
3 litres, or approaching f gallon, per stroke, at a speed of 100 
strokes per minute. Both the cooling tubes are covered with a 
non-conducting material and a casing of wood. Through the 
interior of the carbonic acid tube passes the long tube (a), pro- 
ceeding from the iron shell or retort it is over 16 feet in 
length, with a base of about ± inch, and walls f inch in 
thickness. Being constantly immersed in solid carbonic acid, 
the whole surface of the tube is brought to a temperature 
of —140° C. ( — 220° F.). The tube is slightly inclined, to 
allow of liquid collecting at the lower end. The upper end of the 
tube is curved, and screwed into the howitzer shell (b). The 
sides of this shell are more than 2 inches in thickness ; its 
height is 18 inches, and its diameter 10 inches. 
When oxygen is to be liquefied this shell contains 1^ bs. of 
NEW SERIES, VOL. II. — NO. VI. M 
