PROCEEDINGS OP THE POLYTECHNIC ASSOCIATION. 419 



If exposed to the air long enough, it becomes a dye by oxydation. 

 The oxydation is usually hastened artificially. Besides aniline, 

 there are about a dozen other substances of similar nature, which 

 will produce colors, though generally not quite so brilliant. 

 Many of these substances were already known to the chemist. 

 They are allied to indigo, and many of them can be produced 

 from indigo, from the Spanish name of which aniline derives its 

 name. Aniline may be obtained from dead oil, but it is preferred 

 to obtain it from benzole. Some of these substances are solid. 

 One of them, napthaline, is white, crystalizable and more' vola- 

 tile than camphor. It has a very disagreeable, penetrating odor, 

 and it is to napthaline that coal tar owes, to a considerable 

 extent, its offensive odor. If we had a ready means of separating 

 the napthaline from dead oil, it would produce a very valuable 

 burning oil. Another substance obtained from coal tar is picric 

 acid, derived from the kerosote. The picric acid used in dying was 

 formerly obtained by treating indigo with sulphuric acid, and 

 was sold for a dollar or two per ounce, whereas this is sold for 

 thirty or forty cents per pound. They have not yet succeeded in 

 producing an indigo blue. The oxydable indigo, which is so 

 much in demand for army clothing, has recently doubled in price. 

 A color quite as brilliant as the purples from aniline may be 

 produced from guano. 



The Chairman. — A gentleman stated to me that he had derived 

 from the distillation of oak, hickory and chesnut wood nearly 

 all the substances found in coal tar. 



Prof. Seely. — That is quite true. Most of these substances 

 were first separated from wood tar. In wood there is a large 

 quantity of oxygen, and in coat there is very little. The distil- 

 lates from wood contain more of the compounds of oxygen. The 

 coals contain more nitrogen than the woods, so that a large quan- 

 tity of ammonia is or has been one of the products of the distilla- 

 tion of the former. The fact that coals contain so much nitrogen, 

 seems to point to an animal origin, for nitrogen is not commonly 

 found in plants. 



Mr. Nash gave various reasons for supposing mineral coal to be 

 of animal origin. He stated that the two best dyes were animal 

 productions, the Cochineal and the Tyrian dye, which was an 

 oyster. 



Mr. Yeeder suggested that the Trinidad lake of Asphaltum, 



