Polytechnic Association. 971 



barrel. "When coal tar is subjected to distillation, the liquid portion 

 passes off, and there remains the heavy black pitch which is used for 

 roofing and for pavements. The liquid portion, which comprises 

 about one-fourth of the original coal tar, produces first a light fluid 

 called naphtha, and then a heavy liquid which is called dead oil. The 

 light liquid is a mixture of several hydro-carbons of which benzole is 

 the type. Benzole consists of seventy-two parts of carbon to six 

 parts of hydrogen, which is expressed in the new notation by C 6 H 6 . 

 Other substances found in naphtha are toluene C 7 H 8 ; xylene C 8 H 10 ; 

 cumene C 9 H 12 and cymene C 10 II 14 ; ordinary coal naptha also con- 

 tains traces of olefines. Until recently, only the first two of the ben- 

 zole series have had any practical importance in the arts. But lately 

 another, xylene, is claimed to be a specific for the small-pox. 



After the volatile portions have been removed, there remains this 

 dead oil, which is heavier than water. This was for a long time used 

 as sif fuel in glass-houses. It was then found that the carbolic acid it 

 contains was a most powerful disinfectant and antiseptic. It was found 

 that it would prevent the spread of the cattle disease, that cattle 

 having the disease in its worst form might be placed with others with 

 safety, if they were protected by this acid. It was found, too, that 

 the durability of timber was increased four or five fold by its appli- 

 cation. 



But I wish to-night to invite your special attention, to the beauti- 

 ful colors which have recently been obtained from refuse coal tar. 

 They are naturally subdivided into three groups, the aniline colors, 

 those derived from naphthaline, and the carbolic acid colors. I shall 

 confine my attention wholly to the chemical phase of the subject. 



Benzole is a hydro-carbon. Bringing that in contact with nitric 

 acid, an atom of oxygen carries off an atom of hydrogen, while 

 hyponitric acid takes its place in the benzole ; and we have nitro-ben- 

 zole, which is a very fragrant oil, an artificial oil of bitter almonds, 

 used instead of that substance in the manufacture of soaps. When 

 the nitro-benzole is made to give up its oxygen and take up hydrogen, 

 it becomes aniline. 



Nitrogen is a protean element, which gives rise to a great variety 

 of compounds. Ammonia, is N II 3 , and these three atoms of hydro- 

 gen can be replaced by a great variety of substances. Aniline, or 

 phenylamine, is a similar substance, composed of C 6 II 9 N\ It is 

 ammonia, replacing one atom of hydrogon by phenyl, which is C 6 II 5 . 

 There is no limit to the number of compounds that may be developed 

 on this type; and it opens one of the most important fields of chemi-. 



