CHEMICAL SCIENCE. 



231 



into contact with the outer layer, already in a more advanced state of decom- 

 position, and at a much higher temperature, and hence new reactions take 

 place and new products are formed. Thus, the vapor of water in contact 

 with red-hot charcoal is decomposed, and forms carbonic acid and hydrogen; 

 a part of the carbonic acid is again decomposed by the red-hot carbon to 

 form some carbonic oxide; a part of the nascent hydrogen combines with 

 carbon to form various hydro-carbons; one part of the acetic acid is decom- 

 posed by the high temperature to form acetone and carbonic acid; another 

 part reacts on the wood-spirit and forms methylic acetate; a fraction of the 

 wood-spirit and acetone are also decomposed, producing tarry matters, 

 pyroxanthine, oxyphenic acid, dumasine, etc. To these must be added the 

 influence of ceriain nitrogenized bodies, and we can understand how all these 

 compounds, successively formed under the most favorable circumstances for 

 acting on one another, since they are in the nascent state, and exposed to a 

 high temperature, may give rise to the formation of a great variety of very 

 different compounds, which will be set free either in the stale of a permanent 

 gas or a condensable vapor, and leave fixed carbon as a residue. The same 

 takes place whether wood, coal, bituminous schists, boghead coal, asphalte, 

 peat, resin, oils, or animal matters be distilled; but it is evident that the 

 original composition of the material submitted to dry distillation must pow- 

 erfully influence the nature and composition of the products. In those which, 

 like wood, are rich in oxygen and poor in nitrogen, the pyrogenous products 

 contain much acetic acid and but little ammonia, and consequently have an 

 acid reaction; on the contrary, the matters containing much nitrogen and 

 but little oxygen, like coal and animal matters, give rise to the formation of 

 much ammonia, and the products have an alkaline reaction. 



The following table exhibits the great variety of products which are 

 obtainable from the ordinary coal-tar of gas-works, by distillation and recti- 

 fication : 



Table of the Products obtained by the Distillation and Rectification of Coal-Tar. 



ON THE VALUE OF COAL-TAR AXD ITS PRODUCTS. 



It is interesting, since coal-tar has acquired so important a position in the 

 arts, to trace how its various products successively rise in value. The prices 

 in Paris are given by M. Parisel in a recent paper as follows : 



