§ 247. =Dinitro-benzol=, C₆H₄(NO₂)₂ (ortho-, meta-, para-).--The ortho-compound is produced by the action of nitric acid on benzol, aided by heat in the absence of strong sulphuric acid to fix water. Some of the para-dinitro-benzol is at the same time produced. The meta-compound is obtained by the action of fuming nitric acid on nitro-benzol at a boiling temperature. The physical properties of the three dinitro-benzols are briefly as follows:-- Ortho-d. is in the form of needles; m.p. 118°. Meta-d. crystallises in plates; m.p. 90°. Para-d. crystallises, like the ortho-compound, in needles, but the melting-point is much higher, 171° to 172°. Just as nitro-benzol by reduction yields aniline, so do the nitro-benzols on reduction yield ortho-, meta-, or para-phenylene diamines. Meta-phenylene diamine is an excellent test for nitrites; and, since the commercial varieties of dinitro-benzol either consist mainly or in part of meta-dinitro-benzol, the toxicological detection is fairly simple, and is based upon the conversion of the dinitro-benzol into meta-phenylene-diamine. Dinitro-benzol is at present largely employed in the manufacture of explosives, such as roburite, sicherheit, and others. It has produced much illness among the workpeople in the manufactures, and amongst miners whose duty it has been to handle such explosives. § 248. =Effects of Dinitro-benzol.=--Huber[227] finds that if dinitro-benzol is given to frogs by the mouth in doses of from 100 to 200 mgrms., death takes place in a few hours. Doses of from 2·5 to 5 mgrms. cause general dulness and ultimately complete paralysis, and death in from one to six days. [227] “_Beiträge zur Giftwirkung des Dinitrobenzols_,” A. Huber, Virchow’s _Archiv_, 1891, Bd. 126, S. 240. Rabbits are killed by doses of 400 mgrms., in time varying from twenty-two hours to four days. In a single experiment on a small dog, the weight of which was 5525 grms., the dog died in six hours after a dose of 600 mgrms. It is therefore probable that a dose of 100 mgrms. per kilo would kill most warm-blooded animals. A transient exposure to dinitro-benzol vapours in man causes serious symptoms; for instance, in one of Huber’s cases, a student of chemistry had been engaged for one hour and a half only in preparing dinitro-benzol, and soon afterwards his comrades remarked that his face was of a deep blue colour. On admission to hospital, on the evening of the same day, he complained of slight headache and sleeplessness; both cheeks, the lips, the muscles of the ear, the mucous membrane of the lips and cheeks, and even the tongue, were all of a more or less intense blue-grey colour. The pulse was dicrotic, 124; T. 37·2°. The next morning the pulse was slower, and by the third day the patient had recovered.