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Full text of "Medical Jurisprudence And Toxicology"

ZINC                                                   551

In the case of death occurring from zinc phosphide the post-mortem
appearances are the pale appearance of the mucous membrane of the stomach
and intestine and congested liver and kidneys. The heart is dilated and
flabby with clotted blood. The lungs are congested. The blood is usually
charry red in colour.

Chronic Poisoning.—This occurs among zinc smelters who inhale the
fumes. It has also resulted from drinking water or milk stored in zinc
vessels. Gimlette31 describes an epidemic of zinc poisoning through drink-
ing contaminated water among Sikh and Pathan soldiers stationed in Pahang
in the Malay States. The water-supply was obtained from the rainfall
collected from the galvanized iron roofs of the barracks by means of zinc
gutters and down spouts leading into galvanized iron tanks.

Symptoms.—Digestive disturbances ; dyspepsia; colic with constipation
but more often diarrhoea; aneemia; peripheral neuritis leading to paralysis.

Chemical Tests.—1. Hydrogen sulphide in the presence of ammonia and
ammonium chloride gives a white precipitate, soluble in mineral acids, but
insoluble in acetic acid and sodium acetate.

2.    Potassium ferrocyanide gives a white, gelatinous precipitate of zinc
ferrocyanide, insoluble in hydrochloric acid.    A few drops of bromine water
added to the precipitate produces a greenish-yellow or yellow colour which,
on boiling, forms a green or bluish-green precipitate.

3.    A drop of a neutral solution of a zinc salt is placed on a glass slide
and evaporated to dryness.    Characteristic feathery crystals of zinc sulpho-
cyanide and mercuric sulphocyanide will be seen under the microscope on
the addition of a drop of mercury thiocyanate solution.

Mercury thiocyanate solution isi prepared by dissolving 30 g. of mercuric
chloride and 33 g. of ammonium thiocyanate in 50 cc. of water at room
temperature.

In his annual report for the year 1951, the Chemical Examiner, Madras,
mentions the following procedure adopted by him for the quantitative deter-
mination of zinc phosphide in biological materials : —

As a preliminary test for the presence of phosphine in the material, the
strip test using mercuric bromide paper is performed. If this gives a posi-
tive reaction for phosphine, an aliquot portion of the well-sampled viscus
is placed in a suitable distilling flask of about 500 cc. capacity and the
phosphine in the viscus liberated with dilute hydrochloric acid. The
liberated phosphine is absorbed in a 1.5 per cent solution of potassium per-
manganate for evaluating phosphide phosphorus in zinc phosphide in baits.
The excess of potassium permanganate is destroyed by passing a current of
sulphur dioxide. The resultant solution is boiled down to a convenient
volume, incidentally driving off the sulphur dioxide. Finally, the solution
is made up to a known volume (250 cc. or 500 cc.). An aliquot
portion of the made-up solution is pipetted out in a boiling tube,
diluted to about 25 cc. and the phosphate contents of the solution estimated
by using ammonium molybdate and paramethyl-aminoplienol sulphate. The
intensity of the blue colour developed is compared with the colours developed
from known standard phosphate solutions using a photo electric colorimeter.
The value obtained for the phosphate (P2O5) is multiplied by the factor
1.818 for calculating the amount of zinc phosphide.

Medico-Legal Points.—Zinc is soluble in the weak acids of food; hence
acute poisoning may occur accidentally from eating food cooked in zinc-lined
vessels.

31.   Brit. Med. Jour., Sep. 7, 1901, p. 615.