240 ANNUAL OF SCIENTIFIC DISCOVERY. 



tanning matter which they contain becoming decomposed and transformed, 

 by a process of fermentation, into sugar and gallic acid : which acid, he has 

 ascertained, not only has no dyeing properties, but, on the contrary, that it is 

 injurious, from having a tendency to remove the mordants which are employed 

 to fix the colors on the cloth. It is also known that gallic acid possesses no 

 tanning properties. By adding a small quantity of carbolic acid to the ex- 

 tracts of tanning matter, they can in future be kept and employed by the dyer 

 as a substitute for the substance from which they are obtained, by which will 

 be gained the double advantage of saving labor and obtaining a better effect 

 from the tanning matters. The third substance which passes off in the distil- 

 lation of tar is called heavy oil of tar. This oil contains a singular organic 

 product, first discovered by Dr. Hofmann, of London, and called by him 

 "kyanol," or "aniline," which possesses the property of giving, with bleach- 

 ing-powder and other agents, a magnificent blue color. This fact led Mr. 

 Calvert to observe that this last-mentioned substance, as well as carboazotic 

 and indigotic acids, being produced as weE from indigo as from coal-tar, proves 

 the great similarity and chemical connection which exists between the pro- 

 ducts of these two substances, and induces him to believe it extremely prob- 

 able that these products will be employed within a few years as substitutes 

 for indigo and madder. Laurent has succeeded in obtaining two products 

 from naphthaline, which have a great analogy to the coloring principles of 

 madder. A substance, for instance, called chloronaphthalic acid, has the 

 same composition as the coloring matter of madder, and would be identical if 

 the hydrogen gas was substituted for the chlorine which the acid contains. 

 Hence the chloronaphthalic acid has the property of giving, with alkalies, a 

 most superior red color. "When the coloring principle of madder is treated 

 with nitric acid, a substance called alizaric acid is obtained, which is identical 

 with a substance also obtained from naphthaline, called naphthalic acid. 

 Naphthaline is a solid, white substance, which distills in large quantities 

 during the distillation of tar. It is an interesting fact, that if coals are distilled 

 at a low temperature, the products obtained differ from those which are pro- 

 duced when coals are distilled at a high temperature, as is the usual custom 

 in the manufacture of gas. Without entering into all the details on this point, 

 he mentioned one of the most striking differences of results, namely, that in 

 place of the naphthaline, a valuable lubricating agent, called paraffine, a solid 

 substance, and a large quantity of carburetted hydrogens are also distilled, 

 which, being free from smell, are valuable for commercial purposes, and have 

 received the general name of paraffine oil, or, as Dr. Lyon Playfair remarked 

 in his report of the Great Exhibition of 1851, it is "liquified coal gas." This 

 paraffine oil, when mixed with other oils, is now extensively used in cotton- 

 mills both in England and the United States. Solid paraffine is also obtained 

 in the distillation of peat, and is employed for manufacturing candles, there 

 being added to it about 20 per cent, of wax. These candles are remarkable 

 for their transparency and the pureness of their flame. 





