PRUSSIC ACID. Hydrocyanic or prussic acid, which consists of 1 atom of cyanogen=26,1-1 at. of hydrogen = 1, is prepared by distilling the mercurial bi cyanide in a glass retort with the saturat ing quantity of dilute rnuriatie acid. Prussic acid may also be obtained by precipitating the, mercury by sulphureted hydrogen gas from the solution of its cy anide ; se also by distilling the ferrocya nide of potassium along with dilute sul phuric acid. Prussic acid is a very vola tile light fluid, eminently poisonous, and is spontaneously decomposed by keeping, especially when somewhat concentrated. Prussic acid is also obtained by expos ing the horns, hoofs, and dried blood of animals, with fixed alkali to a red heat. United with iron it is Prussian blue, and for experiments may be abstracted from that pigment. A dog's palate being touched with a glass rod dipped in it, the animal falls dead instantly, and such are its usual effects on animal life.
Prussic acid exists in the skin of the kernel of the seeds which produce it as bitter almonds, the cherry-laurel, &e., &c. It is a compound of carbon and ni trogen, mulled cyanogen, with hydrogen, and hence called hydro-cyanic acid. It operates in medicine in very small closes, on the principle of allaying irritability without disturbing respiration.
The tests commonly employed for the detection of prussic acid, are, the swan, the taste, and the reaction of the suspect ed substance on the addition of certain saline solutions—viz. the solution of ni trate of silver, sulphate of copper, and of any salt of iron containing the black ox ide of that metal. Of these tests the most delicate, but perhaps least certain, is the sense of smell : while the ferruginous so lution, one of the least delicate, is, per haps, the most certain of all.