COAL AND THE COAL-TAR COLORS. 201 



ignorance, must now demonstrate the physical means and the exact 

 locality of the fatal impress — perhaps found as a heart-obstruction, or 

 a minute embolus deep in the labyrinth of the brain, to which some 

 physiological clew may have led. 



Aside from the inherent obscurity and difficulty connected with 

 the subject of medicine, there remains as a heritage of by-gone ages 

 an unwonted mystery associated with it, which should be more rapidly 

 dispelled ; and while the profession is making good progress in elabo- 

 rating and writing its more exact laws, it is the duty of the intelli- 

 gent laity to free themselves from the vestiges of mysticism, and seize 

 upon the more prominent and available facts and principles which 

 are their appropriate possession. 



COAL AKD THE COAL-TAE COLOES. 



By M. DENYS cochin. 



WITHIN thirty years, the agriculture of some countries has been 

 subjected to an unprecedented competition. Vegetable pro- 

 ductions identical with those they were accustomed to furnish have 

 been extracted from stone-coal. Coal was at first employed only as a 

 combustible ; then it gave us gas and illuminating oils. Now it fur- 

 nishes us perfumes and colors ; the flavors of bitter-almonds and of 

 vanilla, and the orange-red of madder, which is no longer cultivated 

 around Avignon. We derive from coal what we used to look for in 

 living plants, and the art of the chemist has fabricated vegetable sub- 

 stances. It would not, however, be correct to say that vegetable sub- 

 stances have been constituted from mineral elements, for coal is not a 

 mineral, but a decomposed vegetable product. It is not pure carbon, 

 but a mixture of hydrocarbons, of combinations which chemistry calls 

 organic, because they proceed from living organisms and preserve a 

 distinctive character peculiar to substances that have been endowed 

 with life. It is not, then, the mineral world that yields us the per- 

 fumes and colors that were furnished by plants and flowers, but an 

 intermediate world in which the remains of the vegetation of past 

 ages are preserved. 



If we heat bituminous coal in a close vessel communicating with 

 cooled receivers, we shall have carbon left in our retort, mixed with 

 a little sulphuret of iron. This is coke. The products of the distilla- 

 tion that pass over will be of two kinds ; a thick liquid, coal-tar, and 

 carbureted hydrogen gases. The gases are used for lighting. Thirty 

 years ago the coal-tar was not used for anything. We shall proceed 

 to inquire what profit is now derived from it. What is it precisely 

 that takes place in the retort ? Shall we believe that the light and 



