tartar bread may find its place as a recognized article of diet.

Acid phosphate of calcium is prepared from bones by treating them with sulphuric acid, setting free a portion of the phosphoric acid. It is supposed to be a useful ingredient of bread, since it restores some of the phosphate said to be lost in the bran.

Acid lactate of calcium has lately been used for a cream of tartar substitute, and in many respects it promises well. It contains the same acid as sour milk, and is prepared from starch by the action of the lactic ferment.

Baking Powders, prepared from soda and cream of tartar chiefly, are, when put up in tin cans, with the maker's name on the label, much more reliable than any other form of bread-raising preparation. About eighty per cent are found to be good; of cream of tartar only sixty per cent are genuine. Sometimes a very little bicarbonate of ammonia is added, to secure a complete neutralization of the acid without leaving an excess of soda. If this amount does not exceed one per cent, it can do no harm. As they are made in large quantities, they are of a more even composition than when cooks guess at the proportions by spoon

fuls. The chief adulterant used is starch or rice flour, sometimes to the extent of fifty per cent. There is not so much adulteration as has often been supposed, if the articles are purchased of the large firms and of reliable dealers. Alum is not infrequently found in powders sold in bulk. The following simple tests may be of use to those who have had a little practice in chemistry.

Good cream of tartar is soluble in eighteen parts of boiling water. Good baking powder is also soluble ; a small quantity of starch present will give a certain opacity to the solution, but if in excess a paste may be formed stiff enough for laundry use. If there is in either case much residue insoluble in water which dissolves in hydrochloric acid, phosphate or sulphate of calcium is to be suspected.

A few drops of barium chloride added to the hydrochloric acid solution will cause a white precipitate, if sulphates are present in the substance under examination. If the phosphates are to be tested for, the acid to be used for a solution is nitric, and to the solution a few cubic centimeters of molybdate of ammonia are added. A fine yellow color or precipitate indicates phosphates. Ammonia is sometimes found in baking

powders. If present, a small lump of potassium hydrate added to the strong aqueous solution will, on heating, cause the ammonia to be given off in the steam, which will then turn red litmus-paper blue.

To test for alum, prepare a fresh decoction of logwood; add a few drops to the solution or substance, and render it acid by acetic acid. A yellow color proves the absence of alum; a purplish red or a bluish color, more or less decided, means more or less alum. If the substance were not acidified, the test might be vitiated by the presence of an alkali, as in the case of a baking powder. Caution: use a new solution, or a new portion of an old one, for each test.

To judge of the quantity of any of the substances, it is necessary to have a standard article with which to compare the suspected one. If the same quantity of each is taken, and it is subjected to the same tests, a very correct judgment of its quality may be formed. Acids should be used in glass or china vessels only.

II

X.

PRINCIPLES OF DIET.

THE

HE food of savage and semi-civilized man has always been of the material most readily obtained; either the flesh of animals killed in the chase, or wild fruits native to his country, or the products of crude agriculture.1 The nations of Northern Europe, down to nearly the middle of the present century, ate rye and barley bread, as wheat could not be profitably grown in that region; and the Esquimaux to-day live upon the product of the seal fishery from necessity, and not from choice.

the

Now, the food products of the whole world are accessible to the people of the United States, through the use of improved methods of transportation, refrigerator car and steamship compartment, through improved methods of preservation, by cold storage, and by the canning process.

and

1 For the diet of ancient peoples, see “ Food and Dietetics,” Pavy, p. 475.

This very abundance brings its own danger; for the appetite is no longer a sufficient guide to the selection of food, as it was in the case of the early peoples who were not tempted by so great a variety.

Many diseases of modern civilization are doubtless due to errors of diet, which might easily be avoided. Many dietaries have been published, but nearly all are only of limited local application, so that, when applied elsewhere, they have failed, and brought discredit upon the whole plan. Only certain broad principles can be laid down, and much intelligent study must be brought to bear upon the question in each community.

The first general principle is suggested by Dr. Pavy, when he calls attention to the fact that the meat-eaters among animals, having to hunt for their food, pass long intervals without any, and when it is obtained gorge themselves with it, and then lie torpid for days. The herbivorous animals, having their food always near them, eat all the time, and are stupid all the time.

Man ought not to imitate either class. It is his privilege to choose such times of eating and such materials for food as will best develop his mental power. Many writers seem to forget this, and to plan