Sulphuric Acid
In order to detect this acid, the solution obtained by treating the organs with water is not distilled but is concentrated to one-sixth of its original volume, and then agitated with ether for about ten minutes. By this treatment the ether takes up the free sulphuric acid, but not the acid sulphates present. After ten minutes contact, the ether is decanted and allowed to spontaneously evaporate. Upon treating the residue, which contains the free sulphuric acid and fatty substances, with water, a solution containing only the sulphuric acid is obtained. Nitrate of baryta is then added to a portion of the fluid: in presence of sulphuric acid, a white precipitate, insoluble in acids, is produced. If this is heated on charcoal before the blow-pipe, a mass is formed, which, when moistened with hydrochloric acid and placed upon a clean silver coin, produces a black spot on the metal. Another portion of the solution is mixed with copper and the mixture evaporated in a tube closed at one end: sulphurous acid is evolved towards the end of the operation. This gas is detected by allowing it to pass over paper saturated with a mixture of iodic acid and starch; a blue coloration is produced which, owing to the transformation of the iodine set free into hydriodic acid, subsequently disappears. (We have never been able to effect the disengagement of sulphurous acid spoken of above when an exceedingly dilute sulphuric acid was used, even upon evaporating the mixture to dryness, notwithstanding Orfila’s statement that the reaction occurs very readily.)