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.

    154/210 (page 140)
    will be readily indicated by an excessive percentage of ash, and their identification effected by the chemical tests applicable to each substance, and referred to under the head of Flour. The addition of such compounds to bread may properly be regarded as a question belonging to past years, for there is no instance on record of any of them having been recently discovered in bread. Sulphate of copper is said to have been occasionally used in this country and on the Continent to improve the colour of bread; and although there are no good grounds for believing that the practice exists at the present time, it may be well to point out a means by which so deleterious an adulterant may be detected and estimated. As a preliminary test, a portion of the crumb of the bread should be soaked in a dilute solution of ferrocyanide of potassium acidified with acetic acid, when, if sulphate of copper has been used, the bread will become of a reddish-brown colour according to the quantity of copper present. To estimate the copper 100 to 150 grams of the bread are moistened with dilute sulphuric acid, and charred over an Argand lamp or in a muffie. The charred mass is digested with water, the extract filtered off, and the residue, after the addition of a few drops of sulphuric acid, dried and thoroughly ignited. The ash, if much copper be present, will be found of a pale green colour. The first filtrate, made slightly acid, is now added to the ash, and after digestion for some time, the extract, which will contain all the copper, is separated by filtration. If any great excess of acid be present, the solution may be neutralised with ammonia, and again made faintly acid with sulphuric acid. The liquid is then introduced into a lipped platinum capsule, in which the copper salt is decomposed by an electric current from a single Grove cell, care being taken, however, to insulate the platinum capsule by placing it on a glass plate. The copper may either be precipitated on the