[R] 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._ _g. Sulphate of copper._--About 200 grammes of the bread under examination are incinerated; the ash treated with nitric acid; the mixture evaporated until it acquires a sticky consistence, and the mass then taken up with water. The aqueous solution is next filtered; an excess of ammonia and several drops of solution of carbonate of ammonia added; the fluid again filtered, the filtrate slightly acidulated with nitric acid, and divided into two parts. It is then ascertained if sulphuretted hydrogen produces in one portion of the solution a brown precipitate of sulphide of copper, and if solution of ferrocyanide of potassium produces in the other a reddish-brown precipitate of ferrocyanide of copper.[S] [S] According to Wagner, if the ash, obtained by incinerating the adulterated bread, is washed with water, shining spangles of metallic copper are separated.--_Trans._ FIXED OILS. Olive oil designed for table use is frequently adulterated with the oils of poppy, sesamé, cotton-seed, pea-nuts, and other nuts; olive oil, intended for manufacturing purposes, is often mixed with colza and nut oils. The tests used are of a rather unsatisfactory character. In all instances, when the chemist is called upon to pronounce as to the adulteration of an oil, it is necessary to execute comparative experiments with the pure oil, and with admixtures arbitrarily prepared: it is only when this is done that the indications obtained are of value. EXAMINATION OF OLIVE OIL INTENDED FOR TABLE USE.