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which the temperature correction may be readily made without reference to tables.

The values of n25 for genuine butter lie between 1.4590 and 1.4620; for oleomargarine the values range from 1.4650 to 1.4700.

The correctness of the adjustment of the instrument may be tested by the "test-plate" which comes with it, using monobromnaphthalene, or by means of distilled water. The theoretical value for the refractive index of water at 18° C. is 1.3330.

Determination of Water.-Directions.-Weigh 2 grams of butter into a shallow metal dish having a flat bottom two inches in diameter and containing a slender stirring-rod two and a half inches long. Heat the butter in the oven at 100° C. for thirty minutes, cool in a desiccator, and weigh. Heat again for periods of fifteen minutes, until the weight remains constant within 2 or 3 milligrams. During the process of heating stir the butter frequently to hasten evaporation of the water.

Determination of Salt.--Directions.-Weigh ΙΟ grams of butter in a small beaker, add 30 c.c. of hot water, and when the fat is completely melted transfer the whole to a separatory funnel. Shake the mixture thoroughly, allow the fat to rise to the top, and draw off the water, taking care that none of the fat-globules pass the stopcock. Repeat the operation four times, using 30 c.c. of water each time. Make the washings up to 250 c.c., mix thoroughly, and titrate 25 c.c. in a six-inch porcelain dish, using silver nitrate with potassium chromate as an indicator.

N

20

Complete Analysis of Butter in One Sample.-Directions.-Weigh about 2 grams of butter into a platinum Gooch crucible, half-filled with ignited fibrous asbestos, and dry it at 100° C. to constant weight. The loss in weight is the amount of water. Then treat the crucible repeatedly

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with small portions of petroleum ether, using gentle suction, and again dry it to constant weight. The difference between this and the preceding weight will be the amount of fat. Now carefully heat the crucible over a small flame or in a muffle until a light grayish ash is obtained. The loss in weight is the amount of curd, and the residual increase in weight over that of the crucible and asbestos is the ash. If desired, the salt may be washed out of the ash and determined by titration with silver nitrate after neutralizing the solution with calcium carbonate.

FLOUR, PREPARED CEREALS, ETC.

This class of foodstuffs is usually in a dry form and not liable to rapid change by micro-organisms, and the examination consists in the determination of their "food value." This may require a simple analytical process, as in the case of the quantity of nitrogen in a sample of "gluten " sold for diabetic patients, or in the case of a brand of flour to be used in a hospital or State institution. It may also require an estimation of the available food-material, as in the case of two kinds of beans or corn. The results of chemical analysis will often put the statements made on packages of breakfast cereals in a different light.

Owing to the extensive use at present of various cereal breakfast foods, many of which are modified from their original composition by cooking or treatment with malt, the extent to which the starch has by this treatment been converted to soluble forms is also an important question for consideration. The actual determination of digestibility belongs to physiological chemistry and need not be taken into consideration here.

Moisture. Directions.-Spread about 2 grams of the finely ground material in a thin layer on a watch-glass and dry it in the oven at 100° C. for five hours. On account of the ready

absorption of moisture by the dried sample, the use of clipped watch-glasses will be found advantageous.

Note. With some substances drying in a current of hydrogen or some inert gas may be necessary, but for most cereals the method given will be found satisfactory.

Ash.-Directions.-Weigh about 2 grams into a platinum dish, such as is used for the determination of solids in milk, and char it carefully. Ignite at a very low red heat until the ash is white, preferably in a muffle.

Notes. If a white ash cannot be obtained in this manner, exhaust the charred mass with water, collect the insoluble residue on a filter, burn it, add this ash to the residue from the evaporation of the aqueous extract and heat the whole at a low red heat until the ash is white.

Some cereals, such as whole wheat and barley, will act destructively on platinum dishes, on account of the phosphates present but can be ignited safely in platinum in the muffle.

Ether Extracts: Fats and Oils.-Directions.-Place the residue from the determination of moisture, as described above, in an extraction-cone and extract it with pure anhydrous ether for sixteen hours. Evaporate off the ether and dry the residual fat at the temperature of boiling water to constant weight.

The ether extract of cereals is not pure fat but may contain more or less coloring matter or resins. Petroleum ether can be used for the extraction, giving results not essentially different from those obtained with anhydrous ethyl ether.

Total Proteids: Determination of Nitrogen by the Kjeldahl Process.*-Principle.-Oxidation of carbon and hydrogen, and conversion of organic nitrogen to ammonium sulphate by means of boiling sulphuric acid in presence of

*Ztschr. anal. Chem., 22 (1883), 366.

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