SULPHATE OF ZINC.
677
Composition. —This salt has the following composition:-
Atoms.
OxWeofZinc................ 1 .
Sulphuric Aeid............... 1 .
Water ...................... 7 .
Eq. Wi... 40 .... 40 .... 03
Per Cent. Bcriütus.
... 28 ...... 32-585
... 28 ...... 30905
... 44 ...... 30-450
Mitscherüch.. . 55-24.. 44-70
CrystaMzed Sulphate of Zinc 1
143
100
100 000 ...... 10000
Purity. —Ammonia added to a Solution of sulphate of zinc throws down awhite preeipitate soluble in excess of ammonia. If any oxide of iron or magne-sia be present it remains undissolved; while any oxide of copper would form anazure blue Solution (cuprate of ammonia.') Ärsenic or cadmium may be de-tected by adding excess of sulphuric aeid to the Solution of the sulphate, and thenpassing a stream of hydrosulphuric aeid through it: the arsenicum and cadmiumare thrown down in the form of sulphurets. The impure sulphate called WhiteVitriol oceurs in irregulär masses; here and there stained yellow with the iron.
Totally dissolved by water. What is thrown down by ammonia is white, and when theammonia is added in excess it is again dissolved. Ün the addition of chloride of barium oracetate of lead they are decomposed.. Ph. Lond.
When a Solution in six waters is boiled with a little nitric aeid, and Solution of ammoniais then added tili the oxide of zinc first thrown down is all redissolved, no yellow preeipitateremains, or a trace only, and the Solution is colourless. PA. Ed.
Physiological Effects. —In small and repeated doses it acts as an astringenton the alimeutary canal, checks secretion, and promotes a constipated condhionof the bowels. It exercises a specific infiuence over the nervou System, mani-fested by its power of removing certain spasmodic affections: hence it is reputedantispasmodic. To the same infiuence is to be referred its power of preventingthe recurrence of intermittent maladies, from which it has principally derived itsdenomination of a tonic. Its astringent effect is not confmed to the bowels, butis manifested in the pulmonary and urethral mueous membranes, the secretionsfrom which it diminishes: hence the advantage of its use in catarrhal affections ofthese parts. It does not appear to possess any power of checking cutaneous ex-halation.
In füll medicinal doses it is a powerful but safe emetic; it excites speedy vo-miting without giving rise to that distressing nausea occasioned by emetic tartar,though this Statement is not in aecordance with the experience of Dr. Cullen,(Treat. of the Mut. Med.) who observes that " in order to render its effects cer-tain, the dose must generally be large; and if this is not thrown out again imme-diately it is apt to continue a disagreeable nausea, or even a vomiting, longer thanis necessary." But this Observation does not agree with the experience of otherpractitioners.
In excessive doses it acts as an irritant poison, causing vomiting, purging, cold-ness of the extremities, and fluttering pulse.
The local action of it is that of an astringent and desiccant, and in a concen-trated form it is a powerful irritant and caustic. Its external use is said to havebeen found fatal in one case, by causing vomiting, purging, and convulsions.(Ohristison, op. cit. p. 468.) Its causticity depends on its affinity for albumenand fibrin.
Uses. —As an emetic it is almost exclusively employed in poisoning, especiallyby narcotics. In these cases it is the best evacuant we can administer, on ac-count of its prompt action. As an internal astringent it is administered inchronic dysentery (Impey, Lond. Med. and Phys. Journ. ix. 55, 1803.) anddiarrhosci, in chronic bronchial affections attended with profuse secretion, and ingleet and leucorrhcea. In the latter cases it is usually associated with terebin-thinate medicines, and is sometimes decidedly beneficial. (See a paper on thissubjeet, by Mr. Graham, in the Edinb. Med. and Surg. Journ. vol. xxvi.)As an antispasmodic ithas been employed with occasional success in epilepsy,