The analysis and adulteration of foods / by James Bell.

  • Bell, James, 1824-1908.
Date:
1881-1883
Catalogue details

Licence: Public Domain Mark

Credit: The analysis and adulteration of foods / by James Bell. Source: Wellcome Collection.

    153/210 (page 139)
    it is found its presence should be dealt with as a clear case of adulteration. Alum is not added to bread to improve its fitness as food, but simply to lead the public to infer from its whiteness and general appearance that the bread has been made from a better description of flour than has really been the case. The principal methods for the detection and estimation of alum have been given under the head of Flour; but the logwood test, when applied to bread, is varied as follows : To about a wine- glassful of water in a porcelain capsule, 5 cubic centimetres of freshly prepared tincture of logwood, and the same quantity of the carbonate of ammonia solution are added. A piece of the crumb of the bread, say about 10 grams, is then soaked therein for about five minutes, after which the liquid is poured away, and the bread is dried at a gentle heat. If alum be present, the bread will acquire a lavender colour or more or less approaching dark blue, according to the quantity of alum which has been added; whereas if the colour be a dirty brown, the bread may be regarded as pure, and, unless under special circumstances, the quantitative estimation of the alumina need not, as already mentioned, be undertaken. As stated on page in, the test is rather negative than positive, and should a lavender or blue colour be produced, a quantitative estimation of the total alumina and silica will be necessary. Although the reliability of the logwood test was for a time doubted by some analysts it has since grown in favour, and is now generally regarded with confidence. This has in great part arisen from the importance attaching to any test which will act as an indicator of the presence of soluble salts of alumina, as it is now well known that both flour and bread often contain a considerable quantity of aluminic compounds without any alum having been added. Earthy salts—such as carbonate of lime or chalk, carbonate of magnesia, sulphate of lime or gypsum, and silicate of magnesia or soapstone—would only be added to give weight. Their presence