Apparatus for Solidifying Carbonic Acid. 297 
quick, or may be kiln-dried. Tallow, or oil, &c. may be rubbed 
upon them, to make them drive more easily, if necessary. 
18th. Abutments are the two supports of a bridge or aqueduct, 
at the ends, and are erected against and connected with the banks, 
on each side of the stream or ravine. They may be constructed 
in various ways, the same as the piers, if any, with which they 
are connected. The abutment fora bridge, on this improvement, 
requires no other strength or solidity, than a pier of equal expo- 
sure, there being no lateral or horizontal pressure, to affect either 
the abutments or piers, and therefore a perpendicular support only 
is required, sufficient to bear up the weight of the bridge, and 
that which may pass over it. One or more draws, for the passage 
of shipping, &c., may consequently be any where placed or con- 
structed, without producing the least injury to this kind of bridge, 
as its strength and safety do not depend, in the least, on being 
connected throughout; except very partially, as respects the ac- 
tion of severe gales of wind, in which case, a structure in one 
entire connected mass, is of course somewhat less liable to be 
acted upon. 
_ 
Arr. XI.—Description of an Economical Apparatus for Solidi- 
Sying Carbonic Acid, recently constructed at the Wesleyan 
University, Middletown, Conn. ; by Joun Jounston, A. M., 
Professor of Natural Science. 
Tue solidification of carbonic acid has of late excited consid- 
erable interest both in Europe and in this country; but the cost 
of the necessary apparatus has been considerable, and many prob- 
ably have on this account, merely, been prevented from making 
any attempt to repeat the experiment. Most of our public lite- 
rary institutions, in which alone in this country such apparatus is 
ever used, are obliged to study economy, and they are therefore 
often liable to be prevented from availing themselves of the ben- 
efits of new discoveries like the present, merely on account of the 
€Xpense of apparatus. 
It is therefore thought a description of an economical apparatus 
for solidifying carbonic acid may be acceptable to the public, 
though we do not pretend to offer any thing new on the general 
Subject, 
Vol. xxxyi1, No. 2.—Jan.-March, 1840. 38 
