The average of the results obtained by Dr. Edward G. Love, New York State Board of Health, from the examination of the crumb of ten samples of the cheaper varieties of wheaten bread were as follows:—
| Per cent. | |
| Water | 42·80 |
| Total ash | 1·0066 |
| Silica and sand | 0·0056 |
| Aluminium (and ferric) phosphates | 0·0053 |
That the addition of alum to bread is prevalent seems to admit of little doubt. The British Public Analysts, in 1879, tested 1287 samples of bread, of which 95 (or 7·3 per cent.) contained alum. Of 18 samples examined, in 1880, in the city of Washington, 8 were adulterated with the salt. The question of the sanitary effects produced by the use of alumed bread is one which has given rise to very extended discussion. According to some authorities, the conversion of alum into an insoluble salt by the fermentation process, which takes place in bread-making, is regarded as a proof that it remains inert, and is consequently harmless in its effects. Others contend that its action as a preventive of excessive fermentation is at the expense of valuable nutritious constituents of the flour, and that its combination with the phosphates present in the grain results in the formation of an insoluble salt which tends to retard digestion. Experiments have been made by J. West Knights, on the comparative action of artificial gastric juice upon pure and alumed bread, which apparently support this latter view.
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 (C6H10O5).—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.
The identification of the various starches is accomplished by means of the microscope. Starch possesses an organised structure which, fortunately, differs in different plants. Besides varying in size, the granules develope in a different manner and form from centres of growth, and therefore exhibit characteristic conditions and positions. These distinctions, together with their effect upon polarised light, are of great utility in the determination of the source of any particular starch. For this purpose, it is necessary to become familiar with the distinctive microscopical appearance of each individual starch. A collection of those most usually met with should be made, and, after careful study, preserved in a dried state for comparative purposes. Polarised light is a very useful adjunct in the examination of starch granules. In the microscopical investigation, a minute portion of the sample is placed upon the glass slide and well moistened with a solution of 1 part glycerine in 2 parts of water; it is then protected by a thin glass cover, which is put on with gentle pressure. The appearance of various starches, under polarised light, is seen in Plate IX., where the cross lies at the hilum or nucleus of the granule and the form and relative size is visible in outline. This plate, and Plates VII. and XII. are copied, with permission, from Bulletin No. 11 of the Chemical Division of the U.S. Department of Agriculture. The original negatives (made by Clifford Richardson) were used, but the auto-types are presented in a somewhat modified form.
PLATE IX.