Note R — IV. MISCELLANEOUS EXAMINATIONS.

If the detection of alum in bread is desired, a portion of the crumb is incinerated in a platinum dish, the ash is treated with concentrated hydrochloric acid, the filtered solution evaporated to dryness, and the residue treated with hydrochloric acid, which now leaves the silica present undissolved. The acid solution is then filtered, nearly neutralized with carbonate of soda, and an alcoholic solution of potassa added in excess. The earthy phosphates present are now precipitated, alumina remaining in solution. The use of aqueous potassa in this case—as well as in the case mentioned in the text—is not advisable, as it is seldom entirely free from alumina. Upon slightly acidulating the alkaline filtrate with hydrochloric acid, and adding carbonate of ammonia, the alumina present is precipitated, and may be dried and tested by means of the reaction with nitrate of cobalt before the blow-pipe. In the quantitative estimation of alumina, the phosphoric acid usually present in the precipitate should be removed. This is done by dissolving the precipitate in nitric acid and immersing a piece of metallic tin in the boiling solution: phosphoric acid is thrown down as a mixture of stannic oxide and phosphate, and the alumina is then precipitated as usual by carbonate of ammonia.—Trans.