As it is not always possible to determine accurately without the aid of chemistry and a microscope whether flour is genuine, the only safe way is to purchase the product of reliable mills. It is always best to obtain a small quantity of flour first, and put it to the test of bread-making; then, if satisfactory, purchase that brand so long as it proves good. It is true economy to buy a flour known to be good even though it may cost more than some others. It is not wise to purchase too large a quantity at once unless one has exceptionally good facilities for storage, as flour is subject to many deteriorating influences. It is estimated that a barrel of good flour contains sufficient bread material to last one person one year; and from this standard it can be easily estimated in what proportion it is best to purchase. TO KEEP FLOUR.--Flour should always be kept in a tight receptacle, and in a cool, dry, well-ventilated place. It should not be allowed to remain in close proximity to any substances of strong odor, as it very readily absorbs odors and gaseous impurities. A damp atmosphere will cause it to absorb moisture, and as a result the gluten will lose some of its tenacity and become sticky, and bread made from the flour will be coarser and inferior in quality. Flour which has absorbed dampness from any cause should be sifted into a large tray, spread out thin and exposed to the hot sun, or placed in a warming oven for a few hours. DELETERIOUS ADULTERATIONS OF FLOUR.--Besides the fraud frequently practiced of compounding whole-wheat flour from inferior mill products, white flour is sometimes adulterated--more commonly, however, in European countries that in this--with such substances as alum, ground rice, plaster of Paris, and whiting. Alum is doubtless the most commonly used of all these substances, for the reason that it gives the bread a whiter color and causes the flour to absorb and retain a larger amount of water than it would otherwise hold. This enables the user to make, from an inferior brand of flour, bread which resembles that made from a better quality. Such adulteration is exceedingly injurious, as are other mineral substances used for a similar purpose. The presence of alum in flour or bread may be detected in the following way: Macerate a half slice of bread in three or four tablespoonfuls of water; strain off the water, and add to it twenty drops of a strong solution of logwood, made either from the fresh chips or the extract. Then add a large teaspoonful of a strong solution of carbonate of ammonium. If alum is present, the mixture will change from pink to lavender blue.