Ste.-Claire Deville on Dissociation. 253 



admit a gas, and at the other to allow its exit. A thin brass tube 

 three-tenths of an inch in diameter passes through the entire 

 length of the tube and through the other hole in each of the 

 corks ; through this tube a rapid current of cold water constantly 

 passes. Two small screens of unglazed porcelain in the interior 

 of the tube separate those parts which are to be heated from 

 those which, projecting from the furnace, remain quite cold. 



A current of pure and dry carbonic oxide was admitted into 

 the tube, and the issuing gas passed into baryta-water. When 

 the temperature attained a bright redness, the baryta- water indi- 

 cated that some carbonic acid was formed. The carbonic oxide 

 had thus been decomposed into carbonic oxide and carbon; the 

 latter was found deposited as fine lampblack in the brass tube, 

 whose temperature even in the hottest part of the apparatus 

 never exceeds 10°. The mass of the water was so great that its 

 temperature was not perceptibly raised by passing through the 

 tube. 



In this experiment there is a strongly heated cylindrical por- 

 celain surface, and a very cold concentric brass one. The par- 

 ticles of carbonic oxide heated in the lower part of the tube 

 ascend, after partial decomposition into carbon and oxygen ; but 

 this current meets the cold and rough side of the brass tube, and 

 the carbon particles are deposited on it mechanically, and, being- 

 kept cold, escape the influence of the oxygen. In all cases 

 the carbon was actually found deposited on the lower surface 

 of the tube. 



If through the above apparatus, which may be spoken of as 

 that of the hot and cold tube, a current of pure dry sulphu- 

 rous acid be passed while the tube is at a temperature of about 

 1200° C, the gas is partially decomposed into sulphur and 

 anhydrous sulphuric acid. The metal tube was made of galvano- 

 plastic copper thickly coated with silver. Silver, it is known, 

 has no action on sulphurous acid at 300°, and far less therefore 

 at 10°. At the close of the experiment the silver tube was 

 found coated with sulphide of silver and with a layer of anhy- 

 drous sulphuric acid. 



Sulphurous acid can also be decomposed by the electric spark 

 of a RuhmkorfFs coil. Two small graduated eudiometers arc 

 filled with pure sulphurous acid gas ; into one of them some solu- 

 tion of chloride of barium in saturated aqueous sulphurous acid is 

 introduced ; into the other some hydrated sulphuric acid. After 

 continuing the action of the spark for some days, the gas entirely 

 disappears and the mercury rises in its place. Much sulphur 

 is deposited, and the tube in which is the barium solution shows 

 a precipitate of sulphate of baryta; while in the other some 

 fuming sulphuric acid is contained. 



