This salt occurs in masses, consisting of crystals which are four-sided
prisms, terminated by four-sided pyramids. Their taste is styptic,
metallic, and slightly acidulous. They are soluble in 2·5 times their
weight of water at 60°, and in less than their own weight of boiling
water, but they are quite insoluble in alcohol. Thus dissolved they
redden the tincture of tournesol.
_Symptoms of Poisoning by Sulphate of Zinc._
This salt, like tartarized antimony, from the high degree of emetic
virtue which it possesses, generally proves its own antidote; still,
however, it must be considered as a poison; for several cases are on
record, where the most alarming symptoms, and indeed death itself, have
been the effect of its ingestion. _Metzger_[317] mentions the case of a
woman, who accidentally ate a trifling quantity of a cake, into which
_White Vitriol_ had been introduced for the purpose of shortening the
days of an old man. The woman died; but the intended victim escaped,
after severe vomiting. _M. Orfila_ has also related several cases of
poisoning by this salt. The symptoms which presented themselves on these
occasions were, an astringent metalline taste, a sense of constriction
in the fauces, so distressing as even to excite in the patient a fear of
suffocation; frequent vomitings; copious stools; pains in the epigastric
region, extending afterwards over the whole abdomen; difficulty of
breathing; frequency of pulse; paleness of the countenance, and coldness
of the extremities.
We have lately heard of a case in which a noble lord swallowed a
solution of white vitriol, which had been sent to him by mistake, for
Epsom salts, to which it bears some analogy. Fortunately, however, the
violent emetic effect which followed removed the poison from the
stomach, and obviated any farther injury.
_Organic lesions discovered on Dissection._
We have no well authenticated dissection of a human being who had died
from the ingestion of this poison. The examination of animals[318] who
have been so killed has shewn nothing more than an inflammation, not
very severe, of the membrane with which it had come in contact;
sometimes dark blood is observed to be extravasated upon the muscular
coat of the stomach and intestines.
_Chemical processes for the detection of Sulphate of Zinc._
The chemist must remember that the _White Vitriol_ of commerce always
contains sulphate of iron, and sometimes sulphate of copper. When
dissolved in distilled water it may be identified by the following
re-agents; _viz._
_a._ _Potass_, and _Ammonia_, precipitate an oxide of a greenish white
colour, easily soluble in an excess of the latter of these alkalies. The
oxide obtained by potass, being washed and dried, and calcined with
charcoal, is revived, provided the temperature be very much elevated. It
should be known, that if the salt has been previously purified, the
above tests will occasion a _white_ precipitate.
_b._ _Prussiate of Potass_ produces a precipitate of a rather deep blue
colour; which, consists of a mixture of the prussiates of zinc and iron.
If the salt has been divested of all impurity, the precipitate will be
white.
_c._ _The Hydro-sulphurets_ instantly occasion a blackish precipitate,
which, like the former, will be found to be a mixture of zinc and iron,
in the state of an hydro-sulphuret. If the salt, however, is pure, its
colour will be white with a tinge of yellow.