Apparatus for Solidifying Carhoruc 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. 



ISth. 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 for a 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 ^e 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. 



Art. XI. — Description of an Economical Apparatus for Solidi- 

 fying Carbonic Acid, recently constructed at the Wesleyan 

 University, Middletown, Conn. ; by John Johnston, A. M., 

 Professor of Natural Science. 



The 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 

 expense 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 oflfer any thing new on the general 

 subject. 



Vol. XXXVIII, No. 2.— Jan. -March, 1840. 38 



