Skip to main content

Full text of "Medical Jurisprudence And Toxicology"

THALLIUM                                                         547

The liver is congested and shows fatty degeneration. The kidneys are con-
gested, the glomeruli are swollen, and cloudy swelling and necrosis of the
cells are seen in the convoluted tubules. The trachea and bronchi are
congested. The lungs are congested with subpleural haemorrhages. The
heart shows fatty degeneration.20

Chemical Analysis.—The detection of thallium in viscera or urine is
carried out as follows 21 : —

A weighed quantity of the material is broken up with hydrochloric acid
and potassium chlorate by Fresenius and Babo method and, when solution of
all the material except fat has been achieved, the liquid is filtered (well
washing the precipitate), and the filtrate boiled until practically all the
excess of chlorine has been driven off or removed by the sulphur dioxide
method. If necessary, it is filtered again, discarding the precipitate. To the
filtrate ammonium chloride and ammonia are added and it is then boiled.
The precipitate which consists of iron, calcium and magnesium chiefly in the
form of phosphates, is filtered off and discarded. It may be advisable to add
a small amount of calcium chloride solution to the liquid before the
ammonia to ensure complete removal of phosphate.

The filtrate is then saturated with sulphuretted hydrogen or an excess
of freshly prepared ammonium sulphide is added; a black precipitate is then,
formed. The precipitate is filtered off, well washed with dilute ammonium
sulphide, and finally with distilled water. It consists of thallium sulphide
together with traces of other metals which precipitate with sulphuretted
hydrogen in an alkaline solution but so far as toxicological analyses are con-
cerned, the only likely metal to be present—and then only in traces—is
copper. When the precipitate is completely washed it is dissolved off the
paper with hot dilute hydrochloric acid. The thallium is converted into
thallous chloride and any trace of the copper which was present as the
sulphide remains behind, for this sulphide is insoluble in dilute hydrochloric
acid. To the solution ammonia is added in slight excess and the liquid is
boilefi. If the process of separation has been completed no precipitate
should occur at this stage. Any precipitate should be filtered off and
discarded. This filtrate is then made very faintly acid, and excess of potas-
sium iodide solution is added. An immediate yellow precipitate of thallous
iodide forms. As there is some tendency for thallous iodide to come down
in colloidal form, the liquid should be boiled and allowed to stand for
twelve hours.

The precipitate is then collected in a weighed Goodh, crucible and is
well washed, first with potassium iodide solution and subsequently with
alcohol, until the washings give no reaction for an iodide. The crucible is
then dried at 120°C. until constant weight is obtained. Although thallous
iodide is very slightly soluble in water (1 : 17,000), it is almost completely
insoluble in potassium iodide solution and in alcohol, so that filtration in the
cold and washing with these reagents will give an accurate estimate of the
amount present. The iodide after weighing may be confirmed as thallium
by dissolving it in a solution of sodium thiosulphate, in which it is only
dissolved with difficulty, whereas lead iodide is readily soluble.

Finally, some of the iodide may be heated in a Bunsen flame on a plati-
num wire and the characteristic green line in the spectrum obtained.

Medico-Legal Points.—Poisoning by thallium is rare as contrasted with
that by lead or mercury, owing probably to the relatively infrequent use of
the former in medicine and industry. A few accidental cases of poisoning
have occurred from the internal administration of thallium acetate or from

20.    Roche Lynch and Scovell, Lancet, Dec. 20, 1930, p. 1342.

21,    Ibid., p. 1342.