The term Arsenious _acid_ was first bestowed upon this substance by _Fourcroy_, since it was found to possess many of the essential habitudes of an acid; as for instance, that of combining with the pure alkalies to saturation. It dissolves in water; but, according to _Klaproth_, although it requires for its solution 400 parts of that fluid, at the temperature of 60° _Fah._ it requires not more than 13, at 212°; and it moreover appears that if 100 parts of water be boiled on the arsenious acid, and suffered to cool, it will retain 3 grains in solution, and deposit the remainder in crystals. This fact shews the great importance of employing boiling water in every chemical examination of substances supposed to contain arsenic. It proves also that a fatal dose of the poisonous mineral may be very easily administered in any watery vehicle, a fact which was denied on the trial of _Ogilvy_ and _Nairne_[221] by _Dr. James Scott_, who deposed that “Arsenic would not dissolve in warm water, but almost instantly subside to the bottom of the vessel,” although, at the same time, he acknowledged that “if it were put into tea with milk and sugar, and stirred about, it _might_ be suspended long enough to kill those who should drink the potion.” It is soluble in alcohol, and in fixed oils, the former taking up two per cent. By the addition of an alkali, an _arsenite_ of great solubility will result, and a solution of extreme virulence may be thus effected. With _lime-water_ arsenious acid produces a white precipitate of _arsenite of lime_, but which is soluble in an excess of the acid. With _magnesia_ it also forms a very soluble, and extremely active, _arsenite_.
_Symptoms of Poisoning by the Arsenious Acid._
_Hahnemann_, in his work on Arsenic, proposes a classification of its effects founded on their relative duration and violence, and which it is our intention to adopt on the present occasion, without any other alteration than that of reversing the order of the classes.
Poisoning by Arsenic may accordingly be considered as admitting of three degrees of intensity, viz. 1st. Where the case, although attended with dangerous symptoms, does not terminate fatally. 2d. Where death does not follow until after a lapse of twenty-four hours. 3d. Where death takes place within twenty-four hours after the exhibition of the poison.