70 EIGHTH REPORT — 1838. 



zinc ; the formation of sulphate of zinc, which is greatly facilitated by 

 the presence of seven atoms of water in union with each atom of acid 

 (that being the number of atoms of water of crystallization contained 

 in it); and, lastly, the proper action of the voltaic circle, which tends 

 to diminish the solution of the zinc. In dilute acid, the first circum- 

 stance retards the action on the zinc alone, and the second facilitate^ 

 its solution ; then the platina surface enables the hydrogen to escape. 

 But in the stronger acid, the voltaic association impedes the solution 

 of the zinc, partly from the evolution of gas being transferred to the 

 platina, and thus the saturated liquid being allowed to accumulate 

 around the zinc plate, and partly from the real effect of the galvanic 

 combination. That the proper tejidency of a voltaic circle is, to dimi- 

 nish the chemical action of the solution on the electro-positive metal, 

 the author endeavoured to show, from the consideration, that in or- 

 dinary solution the electricities thus developed have only an indefi- 

 nitely small portion of liquid to traverse, while in voltaic solution their 

 reunion can only be effected by passing across a column of variable ex- 

 tent, and composed of an imperfectly conducting substance. And, as 

 the action is greater the nearer the plates are to each other, that action 

 ought to attain a maximum when the distance between the plates 

 vanishes, provided this condition could actually be realized. 



On the Construction of Apparatus for solidifying Carbonic Acid, and 

 on the Elastic Force of Carbonic Acid Gas in contact loith the liquid 

 form of the Acid, at different Temperatures. By Robert Addams. 



Mr. Addams prefaced the communication by adverting to the ori- 

 ginal production of liquid carbonic acid by Dr. Faraday, in 1823, and 

 also to the solidification of the acid by M. Thilorier, and then exhibited 

 three kinds of instruments which he (Mr. Addams) had employed for 

 the reduction of the gas into the liquid and solid forms. The first 

 mode was mechanical, in which powerful hydraulic pumps were used 

 to force gas from one vessel into a second, by filling the first with 

 water, saline solutions, oil, or mercury ; and in this apparatus a 

 " gauge of observation" was attached, in order to see when the vessel 

 was filled. The second kind of apparatus is a modification of that in- 

 vented and used by Thilorier. The third includes the mechanical and 

 the chemical methods, and by which, as stated, a saving of a large 

 quantity of acid formed in the generator is effected ; whereas by the 

 arrangements of Thilorier's plan, two parts in three are suffered to rush 

 into the atmosphere, and are lost. With this set of instruments are 

 used two gauges of observation, — one to show when the generator is 

 filled with water by the pumps, and consequently all the free carbonic 

 acid forced into the receiver ; and the other to determine the quantity 

 of li(|uid acid in the receiver. Mr. Addams likewise exhibited other in- 

 struments for drawing off and distilling liquid carbonic acid from one 

 vessel into another, and mentioned some experiments which were in 

 progress, and especially the action of potassium on liquid carbonic 



