vious to its introduction into the test-case; moreover, this method is calculated to show rather the quality of the gluten than its quantity.

The corn-chandlers and bakers, to determine the quality of their flour, make a sample into a paste with a little water, and draw it into a thread, or spread it out into a thin sheet with the thumb and index finger, and they judge of the quality of the dough from the length to which it may be drawn or spread out.

The chemical composition of flour of the same kind may vary between certain limits, so that a slight increase or diminution of its constituents is not an indication of its being adulterated. Thus, Payne found the amount of gluten to vary in four varieties of wheat from nine to twentytwo per cent., and, what is of interest in reference to the bran, a diminution of gluten towards the internal part of the seed, so that the proportion of flour which remains in the bran is richest in gluten. Analogous results were obtained from Fürstemberg in wheat bran.

According to Dumas, the composition of wheat flour is as follows:

The following is the mean between two analyses of the

same flour which I performed in my laboratory:

100 parts of the dry flour contained

The average composition of bran is represented as follows, by Johnstone:

From the large quantity of gluten known to exist in bran, it may be concluded that, in the present system of grinding, the most nutritious portion of the grain is not contained in the flour. The husk in good wheat amounts on an average to fourteen or sixteen per cent. of the entire weight, though the quantity separated at the mill is often not more than one-ninth or eleven per cent.

Microscopical characters of flour.-The microscope affords means of detecting readily any kind of flour from the form of its starch corpuscles. Wheaten flour is often adulterated with an inferior farina, so that it is of the greatest importance that the analyst should be acquainted with its microscopical character. The accompanying woodcuts show the forms of the starch of wheat flour, potato flour, barley flour, rye flour, Indian corn flour, rice flour, arrowroot, sago, bean, oat, and pea.

To obtain the starch for examination, let the flour be kneaded into a thin paste with water, and then squeezed through calico. To extract potato starch, pound the raw potato in a mortar, and then strain the pulp through a cloth; in every case the starch will fall to the bottom of the fluid, in a state fit for microscopical examination. If the observer should wish to see the starch granules in the vegetable cells, he must prepare a very thin section of the grain with a sharp knife or a razor; place the section on the

microscope glass, moisten it with a drop of water, and cover it with a piece of thin glass, when, if the section is sufficiently thin, the structure will, under a low magnifying power, be beautifully displayed. Starch corpuscles, boiled in water, swell, and finally burst, losing their original structure, so that, when intended for microscopical examination, it is important not to extract them with hot water. A glance with the microscope will therefore enable the observer to ascertain at once whether a sample of any kind of flour be pure, or mixed with other farinæ.

3. ADULTERATIONS OF WHEAT FLOUR.-The substances principally employed for the purpose of adulterating genuine wheat flour are potato starch, bean flour, Indian corn flour, rye flour, rice flour, alum, chalk, carbonate of magnesia, silica, clay, bone dust, and plaster of Paris (sulphate of lime). I have already given the reader illustrations of the microscopical characters of the various kinds of starches (see p. 15), and shall add no more to this subject at present.

To determine the nature of the mineral substances with which wheaten flour may be admixed, the analyst must have recourse to chemical methods; still, in many cases, he will also obtain much valuable information from the microscope.

Mineral Adulterations.-1. Carbonate of magnesia and carbonate of lime.-When added, together or individually to new or inferior flours, these substances improve the colour and increase the yield; the adulteration may be carried to the extent of from ten to forty grains of carbonate of magnesia, being mixed with one pound of flour. This practice must be injurious to health. The microscope will aid in this case, by revealing the presence of small specks mixed with the starch corpuscles,