CHAPTER XXI. 



CARBON COMPOUNDS (conHnwed)— PRODUCTS OF THE AROMATIC 

 SERIES— BENZOL— COAL TAR— WOOD TAR— NAPHTHALENE. 



125. Benzene, C,;H,;. —Preparation. — Benzeae or benzol is ex- 

 tracted froiB the tar from the distillation of coal. The products of the 

 distillation are separated by fractional distillation. 



Properties. — Benzene is a colourless, mobile liquid with a peculiar 

 odour, boiling at 80° C. ; its density is 0-880 at 20^ C. Benzene is 

 soluble in alcohol and carbon disulphide ; it is insoluble in water. 

 It dissolves fats and various resins. Absorbed by man, it produces a 

 rather dangerous drunkenness. As an injection it produces rapid 

 anesthesia followed by cramp. 



Action on Plants. — Pure benzene has a corrosive action on 

 plants ; a drop placed on a cabbage leaf makes a hole there in a few 

 days. Blazek examined the action of benzene vapours on the living 

 vegetable cell and found an abnormal division of the nucleus, generally 

 into four without membranous separations. Nemec found the satpe 

 degeneration of the cells of Vicia fabia by a 1 per cent solution of 

 blue vitriol. When cells so modified by the vapour of benzene are 

 placed in a pure atmosphere, the division disappears and the cell be- 

 com'js normal. The action of benzene would thus appear to be 

 unfavourable to the normal evolution of the plant, but this action is 

 only fleetmg and disappears with the cause which produced it. Ben- 

 zene as a proposed substitute for carbon disulphide has the great 

 advantage over the latter of being less injurious to the plant and its 

 roots. The maximum dose borne by a vine in a 4-litre pot is 20 cubic 

 centimetres emulsified with 20 cubic centimetres water. Trials on 

 haricots and weeds show that benzene does not kill plants except in 

 comparatively large doses. Beans stand, as a maximum dose, up to 

 10 cubic centimetres per 2 litres of earth (10 in 2000) ; weeds only 

 have the edges of their leaves dried when -^ gramme of benzene is in- 

 corporated per litre of earth in the soil. 



Action on Insects, — Benzene kills insects by contact and by its 

 vapours. Mouillefert examined its action on phylloxera and found 

 that dipped in benzene the phylloxera and its eggs wei'e killed in five 

 minutes. 



Use. — It has been proposed to substitute benzene for carbon di- 

 sulphide ai^ainst the larva; of the lamellicorns, although the experi- 

 ments of Mouillefert, in 1876, had shown that it was incapable of 

 fulfilling this role against the phylloxera. It has, compai-ed with 

 carbon disulphide, the triple advantage of (1) cheapness ; (2) diffus- 

 ing more slowly in the soil when it is used with the pal injector ; (3) of 

 being much less injurious to the roots of plants. In spite of its 

 (334) 



