298 Apparatus for Solidifying Carbonic Acid. 
The generator A is made of a common mercury flask, several 
of which I have tested and find sufficiently strong. They may 
be purchased in New York for a dollar a piece, or even less. The 
aperture at the neck may be a little enlarged, so as to make it an 
inch or an inch and a quarter in diameter, and the thread of the 
screw re-cut. A plug of cast-steel Bis made of a bar two inches 
in diameter, and turned with a wide and smooth shoulder, so as 
to fit accurately upon a collar of block-tin when screwed into its 
place, as represented in the figure. This collar should be sol- 
dered to the iron ; which is easily accomplished by filing the iron 
bright and tinning it in the ordinary manner, and then melting 
the block-tin and pouring it on, having first screwed a cork into 
the aperture and formed a wall of putty or clay at a sufficient dis- 
tance around it. ‘The shoulder of the plug is readily made to fit 
the collar accurately by screwing it a few times into its place, 
and then removing with a coarse file the parts of the collar upon 
which it touches. In this manner an accurate joint may be made 
without the use of a lathe ; and if the plug does not correspond 
precisely with the axis of the flask it is just as well. 
The faucets or stop-cocks are the most difficult part to con- 
struct, and occasion full half the expense. These in our appara- 
tus are supposed to be essentially the same as are used by others 
for this purpose, but it may not be amiss to insert a description, 
since none has to my knowledge been given. There is this pe- 
culiarity about ours, however; they are inserted in the cast-steel 
plugs, which indeed make a part of them. D is designed to rep- 
resent the plug removed from the generator ; at the upper end of 
it a hole F one inch in diameter is drilled about an inch deep, 
terminating ina hollow cone into which the point G 1s accu- 
rately ground. A small hole éxtends quite througy the plug: 
Around the aperture F a collar of block-tin is fitted to receivé 
the shoulder of the part E, as seen at I, and prevents any pas 
sage around the threads of the screw. Through the axis of the 
part E a hole three eighths of an inch in diameter is drilled, and 
receives the part G which is screwed in from below, the handle 
H being removed. The handle H should be afterwards riveted on. 
Now suppose H E G to be inserted in its place in the cast 
steel plug, as represented at BI, the plug itself being screwed 
into the generator. If H’ be screwed down, the aperture from 
the generator is firmly closed by the conical point G; and by g!¥- 
