It has recently been stated that in flour which has been kept for a long time in sacks, a transformation of the gluten sometimes occurs, resulting in the production of a poisonous alkaloid. This body may be separated by evaporating the ethereal extract of the flour to dryness, and treating the residue with water. The presence of the alkaloid in the filtered aqueous solution is recognised by means of potassium ferrocyanide. The presence of an excessive proportion of moisture is doubtless instrumental in the formation of toxic alkaloids or fungi in old flour and bread. Pure wheaten flour is coloured yellow when treated with ammonium hydroxide, whereas corn meal assumes a pale brown colour, and the meals prepared from peas, beans, etc., become dark brown in colour when tested in this way. Nitric acid imparts an orange-yellow colour to wheaten flour, but fails to change the colour of potato-starch, with which it forms a stiff and tenacious paste. Potato-starch is readily detected by examining a thin layer of the sample on a slide under the microscope, and adding a dilute solution of potassium hydroxide, which, while not affecting the wheaten starch, causes the potato-starch granules to swell up very considerably. Leguminous starches, such as peas, etc., contain approximately 2·5 per cent. of mineral matter; in pure flour, the average proportion of ash is only about 0·7 per cent., and this difference is sometimes useful in the detection of an admixture of the former. The external envelope of the granules of potato-starch offers far less resistance when triturated in a mortar than that of wheat, and upon this fact a simple test for their detection is founded. It is executed by rubbing up a mixture consisting of equal parts of the sample and sand with water, diluting and filtering the paste formed, and then adding to it a solution of 1 part of iodine in 20 parts of water. In the absence of potato-starch, an evanescent pink colour is produced; in case it is present, the colour obtained is dark purple, which in time also disappears. Among the methods which have been suggested for the detection of such accidental impurities as darnel, ergot, and mildew, are the following:--If pure flour is digested for some time with dilute alcohol, the latter either remains quite clear or it acquires a very light straw-colour; with flour contaminated with darnel, the alcohol shows a decided greenish tint, and possesses an acrid and disagreeable taste. In case the alcohol used is acidulated with about 5 per cent. of hydrochloric acid, the extract obtained exhibits a purple-red colour with flour containing mildew, and a blood-red colour with flour containing ergot. When flour contaminated with ergot or other moulds, is treated with a dilute solution of aniline violet, the dye is almost wholly absorbed by the damaged granules, which are thus rendered more noticeable in the microscopic examination.