Another objection to the use of alum is that it is frequently employed for the purpose of disguising the bad quality of damaged and inferior grades of flour. The presence of copper salts in bread is of rare occurrence. Their detection is accomplished by treating a portion of the crumb with a dilute solution of potassium ferrocyanide acidulated with acetic acid, which, in presence of copper, will impart a reddish-brown colour to the bread. If contained in any appreciable proportion, it can be extracted from the ash obtained by the incineration of the bread, and deposited upon the interior of a weighed platinum capsule by the electrolytic method. _Starch_ (C_{6}H_{10}O_{5}).--Starch, which enters so largely into the composition of cereals, is a carbo-hydrate, _i. e._ hydrogen and oxygen are contained in the proportions necessary to form water. In this respect, it is identical with woody fibre, cellulose, and dextrine. The well-known dark-blue colour produced upon the addition of a solution of iodine to starch-paste forms the usual qualitative test for its presence. This coloration is discharged by alkalies and by a solution of sulphurous acid. The quantitative estimation of starch in mixtures is best effected by heating the dry substance in a closed tube for 24 hours, together with a dilute hot alcoholic solution of potassium hydroxide. The hot liquid is next filtered, the residue washed with alcohol, and the filtrate heated with 2 per cent. solution of hydrochloric acid until it ceases to show the blue coloration when tested with iodine. It is then rendered alkaline, and the proportion of starch originally present, calculated from the amount of sugar formed, as determined by Fehling’s solution. Although identical in chemical composition, the various forms of starch met with in the vegetable kingdom vary in size and exhibit characteristic differences in the appearance of the granules. The following are measurements of several varieties of starch granules:-- Millimetre. Wheat ·0500 Rye ·0310 Rice ·0220 Corn ·0300 Bean ·0631 Potato ·1850 The larger granules of potato starch, when suspended in water, subside more rapidly than those of wheat starch; they are also far more readily ruptured.