The fats contained in flour are best separated by treating the meal with cold ether, and evaporating the ethereal extract to dryness. Finally, the inorganic salts or ashes are obtained by incinerating the flour in a platina capsule. The analyst having proceeded so far, and convinced himself of the presence or absence of the normal constituents of the flour under examination, is to continue his investigation with regard to the quantitative composition of the meal; he now requires a balance, but a very delicate instrument is not absolutely necessary. The process to be followed is much the same as that recommended for the qualitative analysis; a weighed sample of the flour, say two grammes (about 30 grs.), is dried in the water bath and re-weighed, the difference showing the quantity of water present. The same sample of flour, or another weighed quantity, if preferred, is now tied up in calico and expressed under distilled water with the thumb and index. finger until it does not yield any more starch. This operation must be performed very carefully, lest any of the fluid should be lost; it will be found necessary to wash the flour with small successive quantities of pure water, collecting the whole fluid into the same vessel. This part of the analysis will last about two hours; when finished, the analyst may throw a little pure water on his fingers with a pipette and add this fluid to the main solution. The string binding the calico bag being now unfastened, the gluten will be found comparatively pure, and by scraping the cloth carefully with a blunt knife it may be removed and conveyed to a watch glass to be dried on the water bath and weighed.1 1 The weight of fibrin obtained by this method is rather below the true estimate; the result would be somewhat more accurate by weighing the dried calico without and with the dry fibrin, and calculating the difference between the two weights, care being taken to wash the calico thoroughly before using it. The starch is determined as follows: ascertain the weight of the fluid obtained by the above process, and allow it to stand undisturbed for some hours in a beaker covered with a glass plate, to enable the starch to subside; then, let a certain amount of the clear liquid be decanted in a weighed capsule, and weigh the capsule again with the fluid; it is next to be evaporated to dryness on a water bath, the residue obtained thoroughly dried and then weighed, the quantity of water being thus determined. Whilst this operation is proceeding the analyst will evaporate also to dryness the remainder of the fluid containing the starch, whose weight has already been ascertained, and this residue, when dry, is also to be weighed. The amount of the starch may be calculated by the following proportion The weight which the clear fluid lost by evaporation is to that of the solid residue it contained, as the weight of the water lost by the evaporation of both fluids is to a or the weight of the whole residue soluble in water; by calculating this proportion, and subtracting the result from the sum of the weight of both residues, the amount of starch will be obtained. I have employed repeatedly this method, and believe it to give correct results. To determine the amount of sugar in the sample of flour examined, the dry residue from the clear fluid is boiled with alcohol, and the solution decanted; the residue being again dried, and weighed, and subtracted from the weight of the residue previous to the addition of alcohol, the difference between the two weights will represent the quantity of sugar. By calculating the following proportion the total amount of sugar is ascertained. The weight of the residue in the clear fluid is to the weight of the sugar obtained, as the weight of the residue of the whole clear fluid, the result of a previous calculation, is to æ. : The weight of the dextrine has been already determined it is the difference between that of the sugar and the weight of the residue left by the evaporation of the clear fluid; the total amount is to be calculated by a proportion similar to the above. The albumen of flour is usually weighed with the dextrine. The quantity of fatty matters contained in a given amount of flour can be ascertained by treating a weighed quantity of flour with ether, evaporating this extract to dryness, and weighing the residue. The weight of the inorganic salts is determined by burning a known quantity of the flour. For the determination of the quantity and quality of gluten, an ingenious contrivance has been invented by Mr. Hubart, and termed the aleurometer, which is described in Dr. Hassall's book. It consists of a hollow copper cylinder, about six inches long, and from three quarters of an inch to an inch in diameter. It has two principal parts, the one, about two inches long, is closed at one end, forming a kind of cup capable of containing about 200 grains of fresh gluten; it screws into the remainder of the cylinder. The cylinder being charged with gluten, is heated to about 420° in an oil bath; by this treatment the gluten swells more or less in the tube according to its quality; its increase or decrease in bulk may be measured with a graduated stem. Good flours furnish a gluten which augments to four or five times its original bulk; but bad flour gives a gluten which does not swell, becomes viscous and nearly fluid, adhering to the sides of the tube, and giving off occasionally a disagreeable odour, whilst that of good flour merely suggests the smell of hot bread. To this we may add, that the practical importance of the instrument is diminished by the necessity of separating the gluten from the flour pre The starch is determined as follows: ascertain the weight of the fluid obtained by the above process, and allow it to stand undisturbed for some hours in a beaker covered with a glass plate, to enable the starch to subside; then, let a certain amount of the clear liquid be decanted in a weighed capsule, and weigh the capsule again with the fluid; it is next to be evaporated to dryness on a water bath, the residue obtained thoroughly dried and then weighed, the quantity of water being thus determined. Whilst this operation is proceeding the analyst will evaporate also to dryness the remainder of the fluid containing the starch, whose weight has already been ascertained, and this residue, when dry, is also to be weighed. The amount of the starch may be calculated by the following proportion : The weight which the clear fluid lost by evaporation is to that of the solid residue it contained, as the weight of the water lost by the evaporation of both fluids is to a or the weight of the whole residue soluble in water; by calculating this proportion, and subtracting the result from the sum of the weight of both residues, the amount of starch will be obtained. I have employed repeatedly this method, and believe it to give correct results. To determine the amount of sugar in the sample of flour examined, the dry residue from the clear fluid is boiled with alcohol, and the solution decanted; the residue being again dried, and weighed, and subtracted from the weight of the residue previous to the addition of alcohol, the difference between the two weights will represent the quantity of sugar. By calculating the following proportion the total amount of sugar is ascertained. The weight of the residue in the clear fluid is to the weight of the sugar obtained, as the weight of the residue of the whole clear fluid, the result of a previous calculation, is to æ. : The weight of the dextrine has been already determined it is the difference between that of the sugar and the weight of the residue left by the evaporation of the clear fluid; the total amount is to be calculated by a proportion similar to the above. The albumen of flour is usually weighed with the dextrine. The quantity of fatty matters contained in a given amount of flour can be ascertained by treating a weighed quantity of flour with ether, evaporating this extract to dryness, and weighing the residue. The weight of the inorganic salts is determined by burning a known quantity of the flour. For the determination of the quantity and quality of gluten, an ingenious contrivance has been invented by Mr. Hubart, and termed the aleurometer, which is described in Dr. Hassall's book. It consists of a hollow copper cylinder, about six inches long, and from three quarters of an inch to an inch in diameter. It has two principal parts, the one, about two inches long, is closed at one end, forming a kind of cup capable of containing about 200 grains of fresh gluten; it screws into the remainder of the cylinder. The cylinder being charged with gluten, is heated to about 420° in an oil bath; by this treatment the gluten swells more or less in the tube according to its quality; its increase or decrease in bulk may be measured with a graduated stem. Good flours furnish a gluten which augments to four or five times its original bulk; but bad flour gives a gluten which does not swell, becomes viscous and nearly fluid, adhering to the sides of the tube, and giving off occasionally a disagreeable odour, whilst that of good flour merely suggests the smell of hot bread. To this we may add, that the practical importance of the instrument is diminished by the necessity of separating the gluten from the flour pre |