418 TRANSACTIONS OF THE AMERICAN INSTITUTE. 



the coal will combine with the hydrogen, one atom of nitrogen to 

 three of hydrogen, forming ammonia, and some of the oxygen will 

 combine with the hydrogen, one atom of each, forming water, &c. 

 In making gas, we also make all these different substances, and 

 it is necessary to separate, as far as possible, those which are 

 not useful for illumination. Some of them have not yet been 

 successfully separated, as sulphur, for instance, which gives the 

 gas an offensive odor in burning. There is free ammonia in all 

 gas, and it is carefully separated. The water, as it condenses, 

 will separate from the oily products. After the latter are 

 removed, the coal tar is left. The substance which this coal tar 

 contains, probably in the greatest quantity, is kreosote, which has 

 an antiseptic property. The several substances may be entirely 

 separated by chemical reagents ; but it is found most easy to 

 separate them by distillation. The most volatile substance rises 

 first, and thus you obtain one substance after another until you 

 have distilled away perhaps one-half of the original tar. In the 

 actual manufacture, the first twentieth is reserved for a special 

 purpose, and called "light oil." Then about one-fifth is a thick- 

 ish, dark colored and very offensive oil, which is called " dead 

 oil." This is used as an antiseptic in preserving railroad timber. 

 It is of about the consistency and color of molasses. The light 

 oil comprises various substances, boiling at a temperature vary- 

 ing from the boiling point of alcohol to the boiling point of water. 

 When distilled once, naptha is produced, which is used in Eng- 

 land for burning. By treating this naptha with sulphuric acid 

 most of the color is taken out, and also most of the disagreeable 

 emell, and it is then used for burning and for manufacturing var- 

 nishes. About five per cent, of the light oil is what is properly 

 known as benzole. What are called benzole and benzine in 

 America, have generaOy no benzole in them. The benzole which 

 is separated from coal tar is the basis of all the colors which have 

 been spoken of. In composition it is simply a hydrocarbon, C12, 

 He. 



The general method of producing the colors is as follows : 

 One atom of hydrogen is taken away and replaced by an atom 

 of nitrous oxyde, NO*, which forms a substance called artificial 

 bitter almond oil. The oxygen is then entirely taken out, and 

 one or two atoms of hydrogen is put in its place, so that the 

 formula becomes C12, H7, N. In that shape it is called " a?jt. 

 /tne," which is a thick oily substance, of spicy odor and taste 



