CHEMICAL SCIENCE. 229 



creosote by the action of nitric acid, and it can be employed at once 

 for dyeing. If I take a skein of silk and agitate it for a little in 

 carbazotic acid, it -will take on the dye without any previous prepara- 

 tion, and assumes a beautiful yellow color. This material has also 

 been lately employed, as almost everything is employed, for various 

 other useful purposes. It is an excellent antiperiodic, like quinine, 

 only when employed it dyes the skin of the patients yellow, and they, 

 therefore, have a sort of artificial jaundice. But it has also been 

 suggested for another purpose. It may be mixed with arsenic and 

 other poisons for the purpose of rendering them more ready of detec- 

 tion. It imparts to the arsenic a bitter taste, and it also turns the 

 person to whom it is administered yellow, and in a case of slow poison- 

 ing this yellow appearance would be an indication that there was 

 something wrong. 



Cressylic acid, another of the compounds of crude tar-oil, is not 

 much employed in the separate state. 



I now pass to the neutral hydrocarbons. The neutral hydrocar- 

 bons are also various. They are called benzol, toluol, xylol, cumol, 

 cymol, and a great many other names with which I will not trouble 

 you. They are compounds of hydrogen and carbon, and possess 

 many degrees of volatility. For instance, benzol boils at 177. This 

 is one of the most useful of the substances. It is made from crude 

 naphtha by a simple operation, taking advantage of its low tempera- 

 ture of ebullition. Here is a benzol still. The crude naphtha is 

 placed in this still. It is a double still, into which steam is sent from 

 this steam-boiler in order to heat the crude naphtha. The top of the 

 still, you will observe, passes through a cistern of water. That cis- 

 tern of water is kept at the boiling point of benzol, 177, and the 

 vapor of the naphtha passes through the heated vessel, which is 

 heated to 177. Benzol distils over at 1 77 ; but toluol, cumol, cymol, 

 and the others, boil at a much higher temperature. Therefore they 

 are condensed at that temperature, and fall back into the still. The 

 separation is, therefore, effected simply by means of keeping the ben- 

 zol at its own boiling temperature, and cooling the others below 

 theirs. It is a very volatile substance. It, no doubt, adds much to 

 the illumination of our coal gas. 



Now, this body, when acted upon by nitric acid, produces nitro- 

 benzol. I must call your attention to nitro-benzol a little scientifi- 

 cally. Benzol has the formula C 12 H 6 that is, it contains twelve 

 equivalents of carbon, and six of hydrogen. In nitro-benzol one of 

 these equivalents of hydrogen goes out, and one equivalent of oxide 

 of nitrogen, NO 4 , goes in and substitutes it, and then forms nitro- 

 benzol, a substance which by itself possesses some peculiar characters. 

 It smells strongly of bitter almonds, and it is employed now instead of 

 bitter almonds, which is poisonous, for making common almond soap. 

 The common almond soap which we buy is now perfumed with nitro- 

 benzol. It is also employed in confectionery as a substitute for bitter 

 almonds. It is much better for that purpose, because the bitter 

 almonds contain prussic acid, and by the use of too large a quantity 

 by our cooks we may poison our friends. There is no chance of that 

 taking place when nitro-benzol is used. It is the basis from which we 

 derive our tar colors, and the mode in which it is used for this pur- 

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