Hydrocyanic Acid, Scheele’s

Syn. Acidum Hydro cyan i cum Scheelii . The original proce of Scheele does not yield an acid of uniform strength, and is probably never followed. It is therefore impo ible to state precisely what is intended when Scheele’s acid is prescribed, or to understand why it should be preferred by certain physicians to the British Pharma copœia preparation, which is of a known and definite strength. As prepared by different makers it has been found to contain from three to five per cent. of anhydrous acid. The following is Scheele’s proce :— Mix two ounces of Pru ian blue, with six ounces of red precipitate of mercury, and add six ounces of water. Boil for some minutes, constantly agitating; pour the whole on a filter and wash the residuum on the filter with two ounces of hot water, which is to be added to the filtered liquor. Add to this an ounce and a half of clean iron filings, and three drachms of sulphuric acid; shake well and let it settle; then pour the clear liquor into a retort, and distil a fourth part into a receiver well luted and kept cold.