These are the alkaline arsenites and arseniates, arsenic acid, arsenious acid, the black oxide or fly-powder, and arseniuretted-hydrogen. With regard to arsenic acid, and the alkaline arseniates and arsenites, it is probable, from their effects in medicinal doses, that they are as active as the white oxide, if not more so. But they have not been particularly examined, as they are not objects of great interest to the medical jurist. The fly-powder or black oxide is very active. Renault found that four grains killed a middle-sized dog in ten hours.[583] It has been likewise known to prove quickly fatal to man. In a French journal there is a case related which ended fatally in sixteen hours;[584] and in the Acta Germanica is an account of four persons, who died in consequence of eating a dish of stewed pears poisoned with it, and of whom three died within eighteen hours.[585] The dose is not mentioned; but it is probable from the collateral circumstances that it was not considerable. Arseniuretted-hydrogen is probably the most active of all arsenical compounds. The celebrated German chemist Gehlen, having accidentally inhaled a small portion of it, died in nine days with the usual symptoms of arsenical poisoning. In Dr. O’Reilly’s case, which proved fatal in seven days, it was computed that the equivalent of twelve grains of oxide had been inhaled. And Dr. Schlinder’s patient had inhaled a quantity of gas corresponding with only an eighth of a grain of sesquioxide; yet he appears to have made a narrow escape.[586] It is of some consequence to settle with precision the power of the white oxide. Witnesses are often asked on trials how small a quantity will occasion death? It is obvious that this question admits only of a vague answer: It can be answered at all only in reference to concomitant circumstances, and even then but presumptively. Nevertheless, it is right to be aware what facts are known on the subject.