Public health laboratory work / by W. Watson Cheyne, W.H. Corfield and Charles E. Cassal.

  • Watson Cheyne
Date:
1884
Catalogue details

Licence: Public Domain Mark

Credit: Public health laboratory work / by W. Watson Cheyne, W.H. Corfield and Charles E. Cassal. Source: Wellcome Collection.

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    appearances of the different starches under the microscope enables this to be done with ease in the case of flour; but with bread, inasmuch as the process of manufacture alters these appearances, the starch granules swelling and burst- ing, the problem is much more difficult. The chemical examination of flour resolves itself chiefly into determining the percentages of Water, Gluten, Ash, and the presence of Alum, and its quantity, if present. The amount of water in flour is ascertained by drying one gramme in a dish, and the amount of ash by burning two or three grammes. For bread larger quantities are necessary. The more water the less is the value of the article ; flour should be rejected if it contains more than i8 per cent. If the ash be more than 2 per cent, mineral adulteration or impurity is present. An easy method of detecting large quantities of mineral impurity is to shake up the flour with chloroform, when the flour floats, and the foreign mineral impurities fall to the bottom of the vessel. Gluten is esti- mated in flour by washing away the starch from a weighed quantity : good flour contains from 8 to 12 per cent. Alum in Flour and Bread,—The presence of alum is most easily detected by treatment with a tincture of logwood and carbonate of ammonia. If alum is present, a blue or green colouration is obtained ; the flour should previously be well mixed with water and the bread should be allowed to dry. If a blue colour be obtained a further examination is necessary, and the exact amount of alumina present must be separated out from a weighed quantity of the flour or bread and weighed. The process is a somewhat long one, and it will hardly be necessary to describe it here. There have been rare cases of poisoning which have occurred through the presence of lead in flour, which has been introduced through the repairing of mill stones with lead. Arsenic has also been found in flour, having been introduced accidentally, and plaster of Paris (sulphate of lime) has been fraudulently sold with flour. Teay Coffee, Cocoa and Chocolate.-—The examination of tea does not present much difficulty. The presence of foreign
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