COAL AXB THE COAL-TAB COLORS. 211 



heavy oils of coal-tar. It forms a part of the deposit of solids which 

 forms when the heavy oils are left standing in the cold, from which 

 are obtained the crystals of naphthaline. When this deposit is raised 

 to a temperature of 250° C. (482° Fahr.), the naphthaline and the in- 

 definite oily substances are distilled away, and there is left anthracene, 

 with some impurities. The impurities may be removed by means of 

 the very light oils of petroleum, which dissolve them and leave the 

 anthracene ; or by the light oils of coal-tar, which dissolve the anthra- 

 cene and leave them. When anthracene has been sufficiently purified 

 it is submitted to the action of oxidizing agents, and anthraquinone is 

 obtained by precipitation as a resultant. By this direct process we 

 have made a ternary body of our hydrocarbon, and have combined it 

 with a proportion of oxygen which we can not increase by any further 

 process of a direct character ; but the alizarine which we are seeking 

 to get is richer in oxygen than anthraquinone. The second degree of 

 oxidation has to be attained by an indirect process ; we bring it about 

 by withdrawing some atoms of hydrogen from the molecule and sub- 

 stituting for them molecules containing oxygen. The authors of the 

 synthesis accomplished it in a process of two steps, by putting bromine 

 in place of hydrogen and the elements of water in place of the bromine. 

 But bromine is expensive, and so the manufacturers now make alizarine, 

 not from a bromized but from a sulphureted anthraquinone. Of all 

 the coloring substances derived from coal-tar, alizarine is the one which 

 is now made in the greatest quantity. According to the report of M. 

 Wiirtz, made in 1878, eight factories, two of which were very exten- 

 sive, were then in full activity in Germany, two in Switzerland, one in 

 England, and one in France, which last the proprietors had had the 

 courage to establish in the very center of the madder-raising district. 

 The quantity of alizarine then produced was estimated at 3,500 kilo- 

 grammes, or nearly 9,000 pounds daily, and it has doubtless been since 

 considerably increased. 



Anthracene, the basis of the manufacture of alizarine, is relatively 

 abundant in coal-tar, forming sometimes from seven to eight per cent 

 of its mass. It has been observed that coal-tar is rich in anthracene in 

 proportion as it is poor in toluene, and M. Berthelot has explained the 

 fact by showing that toluene, decomposed by heat, produces anthra- 

 cene ; hence the relative amount obtained of either is likely to vary 

 according to the temperature-conditions of the distillation. The dif- 

 ferences may also probably depend upon the character of the coal and 

 of the matter first employed at the point of departure of all the opera- 

 tions. But, as we have said, this point of departure is essentially un- 

 known. All of our products have been obtained from a vegetable or 

 organic, not from the primary mineral, carbon ; not from carbon either, 

 but from compounds of carbon and hydrogen of a character which we 

 have not yet been able to produce by synthesis of the primary min- 

 eral elements, but which the sun stored up for us ages ago, working 



