ON THE SOLIDIFICATION OP CARBONIC ACID. 305 
shoulder of the screw. There is a hole in the head of the 
screw E for the reception of a long, strong, iron bar. 
The copper cup, N, 14 inches wide, and 9 inches long, 
holds about 12 fluid ounces. There is a little handle at the 
top, and a copper wire at the bottom, which make the whole 
length a little less than that of the cavity of the generator. 
This cup is used to introduce the sulphuric acid. 
The brass tube between the generator and receiver is divi- 
ded into two parts of equal length, which admit of being 
united by means of a conical juncture, kept tight by the stir- 
rup and screw, K, K. Each of these portions of the tube 
may be closed or opened at pleasure by a stop-cock. One is 
placed at I, another at J; so that when the receiver is being 
separated from the generator, 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 indis- 
pensable. 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 to I and J. L is a 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 T. 
The gauge for measuring the pressure is peculiar. Into a 
wrought iron box, S, are inserted, by screws, two sockets, 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 rise above the mercury. 
Two strong barometer tubes, R and M, are cemented* into 
♦The cement used was made of shell lac 3 or 4 parts, white or crude 
turpentine 1 part, melted at as low a temperature as possible so as not to 
