322 Chronicles of Science. [April, 



combination of the separated elements ; this can only be effected by 

 causing these elements to come in contact with a relatively very cold 

 atmosphere. By a modification of his apparatus, M. Deville has suc- 

 ceeded in effecting the dissociation of carbonic oxide, sulphurous, 

 hydrochloric, and carbonic acids, and ammonia. He passes through a 

 furnace a porcelain tube, with corks at each end, through which is 

 introduced a small brass tube. In the space between the porcelain and 

 the brass tube, a current of the gas under experiment is allowed to 

 flow by means of glass tubes passing through the corks. A rapid 

 current of water is constantly passing through the brass tube, which is 

 thereby kept cold, whilst the porcelain tube can be raised to a white 

 heat. The apparatus being thus arranged, a current of pure dry car- 

 bonic oxide is passed through the porcelain tube, and as it issues out 

 it is conducted into baryta water, by means of which the presence of 

 carbonic acid may be shown. As soon as the porcelain tube attains a 

 red heat, the carbonic oxide is decomposed into oxygen (which burns 

 a further quantity of carbonic oxide into carbonic acid), and carbon, 

 which attaches itself in the form of lamp-black to the brass tube tra- 

 versing the porcelain tube. 



We have thus in a very small space a greatly heated cylindrical 

 porcelain surface, and a very cold brass surface. The molecules of 

 carbonic oxide heated in the porcelain tube, after having been par- 

 tially decomposed into oxygen and carbon, encounter the cold side of 

 the brass tube, when the particles of carbon mechanically attach them- 

 selves to it. Here being cooled by the water circulating in the metal 

 tube, the carbon escapes the action of the oxygen or carbonic acid. 

 The brass tube is, in fact, found to be blackened by the carbon when 

 the apparatus is carefully taken to pieces, and its quantity is in pro- 

 portion to the quantity of carbonic acid contained in the escaping gas. 

 In the experiment with sulphurous acid, the inner metallic tube 

 which carries the stream of cold water was silvered on its external 

 surface. After the current of sulphurous acid had continued for some 

 hours, the silver surface was found to be blackened or sulphuretted, 

 and at the same time covered with a layer of anhydrous sulphuric 

 acid, showing that sulphurous acid had been dissociated or completely 

 decomposed into sulphur, which was deposited on to the silver and 

 oxygen which combined with the excess of the acid to form sulphuric 

 acid. Until now sulphurous acid has been considered completely un- 

 decomposable by heat. In the experiment with hydrochloric acid, 

 the author amalgamated the silvered surface of the cold tube with a 

 very small amount of mercury, and so obtained a very brilliant sur- 

 face. After pure hydrochloric acid gas had passed for some hours, 

 this surface was found covered with chloride, and by a peculiar ar- 

 rangement M. Deville was able to collect some hydrogen. Carbonic 

 acid and ammonia were decomposed with the induction spark. 



A very ingenious maximum thermometer has been described by 

 Mr. Twining.* It is a spirit thermometer, having about one-third of 

 the way up the tube a small bulbous enlargement, in which is lodged 



* 'Chemical News,' vol. xi. p. 20. 



