204 POISONS : THEIR EFFECTS AND DETECTION. [§§ 255 , 256 . 
even the conjunctiva) have been of a marked blue colour, giving the 
sufferer a strange livid appearance. In other cases there has been 
jaundice, the conjunctive and the skin generally being yellow, the lips 
blue. Occasionally gastric symptoms are present. Sleeplessness is 
common, and not infrequently there is some want of muscular co¬ 
ordination, and the man staggers as if drunk. In more than one case 
there has been noticed sudden delirium. There is in chronic cases always 
more or less anaemia, and the urine is remarkable in its colour, which 
ranges from a slightly dark hue up to positive blackness. In a large 
proportion of cases there is ophthalmic trouble, the characteristics of 
which (according to Mr Snell) are “ failure of sight, often to a consider¬ 
able degree, in a more or less equal extent on the two sides ; concentric 
contraction of visual field with, in many cases, a central colour scotoma ; 
enlargement of retinal vessels, especially the veins ; some blurring, 
never extensive, of edges of disc, and a varying degree of pallor of its 
surface—the condition of retinal vessels spoken of being observed in 
workers with the dinitro-benzol, independently of complaints of defective 
sight. Cessation of work leads to recovery.” 
§ 255. Detection of Dinitro-benzol. —Dinitro-benzol may be detected 
in urine, in blood, and in fluids generally by the following process :— 
Place tinfoil in the fluid, and add hydrochloric acid to strong acidity ; 
after allowing the hydrogen to be developed for at least an hour, make 
the fluid alkaline by caustic soda, and extract with ether in a separating 
tube ; any metaphenylene - diamine will be contained in the ether ; 
remove the ether into a flask, and distil it off ; dissolve the residue in 
a little water. 
Acidify a solution of sodium nitrite with dilute sulphuric acid ; on 
adding the solution, if it contains metaphenylene-diamine, a yellow to 
red colour will be produced, from the formation of Bismarck brown 
(triamido-phenol), 
XII.—Hydrocyanic Acid. 
§ 256. Hydrocyanic Acid (hydric cyanide) —specific gravity of liquid 
0-7058 at 18° C., boiling-point 26-5° (80° F.), HCy = 27.—The anhy¬ 
drous acid is not an article of commerce, and is only met with in the 
laboratory. It is a colourless, transparent liquid, and so extremely vola¬ 
tile that, if a drop fall on a glass plate, a portion of it freezes. It has 
a very peculiar peach-blossom odour, and is intensely poisonous. It 
reddens litmus freely and transiently, dissolves red oxide of mercury 
freely, forms a white precipitate of argentic cyanide when treated 
with silver nitrate, and responds to the other tests described 
hereafter. 
