757. _To detect Copper in Liquids._--Spirit of hartshorn mixed with them, turns them blue. Therefore tea is not dried on copper, as an infusion of it is not turned blue by this mixture. Cider, being passed through brass pots, is detected by this experiment.--_Dr. Moyes' Lectures._ 758. _To detect the Mixture of Arsenic._--A solution of blue vitriol dropped into any liquid in which arsenic has been put, will turn it green. 759. _To test Mushrooms._--Rub the upper skin with a gold ring or any piece of gold: the part rubbed will turn yellow if it is a _poisonous fungus_. 760. _To prepare Salt._--Set a lump of salt in a plate before the fire, and when dry, pound it in a mortar, or rub two pieces of salt together; it will then be free from lumps, and in very fine powder. 761. _To make Cheap and Good Vinegar._--To eight gallons of clear rain water, add three quarts of molasses; turn the mixture into a clean tight cask, shake it well two or three times, and add three spoonsful of good yeast, or two yeast cakes. Place the cask in a warm place, and in ten or fifteen days, add a sheet of common wrapping-paper, smeared with molasses, and torn into narrow strips, and you will have good vinegar. The paper is necessary to form the "mother," or life of the liquor. 762. _To prevent Mouldiness._--The best preventive is any of the essential oils, as the oil of lavender, cloves, peppermint, &c. Russia leather, which is scented with the tar of the birch-tree, is not subject to mouldiness, and books bound in it will even prevent mouldiness in other books bound in calf, near which they happen to lie. Aromatic seeds are not subject to mould, and gingerbread, or cakes containing caraway seeds are far less liable to mouldiness than plain bread. Children have been poisoned by eating mouldy bread. 763. _To keep Fruits._--To preserve fruits, you must keep them in a room rather above the ground floor, sheltered alike from the sun and damp; it is even prudent, in order to avoid opening the windows, to let out the humid exhalations of the fruit, to have a stove in the room, and light a fire in it now and then. The decaying fruit should be carefully removed. Cherries, grapes, &c., are kept sound by hanging them to threads, and then inclosing them in new boxes or barrels; these are closed as tightly as possible, and deposited in a dry place. Some preserve them by laying them in sawdust or bran. 764. _To preserve Apples._--Dry a glazed jar perfectly well, put a few pebbles in the bottom; fill the jar with apples, and cover it with a bit of wood made to fit exactly; and over that, put a little fresh mortar. The pebbles attract the damp of the apples. The mortar draws the air from the jar, and leaves the apples free from its pressure, which, together with the principle of putrefaction which the air contains, are the causes of decay. Apples, kept thus, have been found quite sound, fair, and juicy, in July.