Put a small quantity of the suspected liquid into a test-tube, and add to it, drop by drop, strong sulphuric acid till it becomes warm, taking care not to raise the temperature above 122° Fabr. Then add from 2 to 5 drops of syrup, made with 5 parts of sugar to 4 of water, and shake the mixture. If the liquid contain bile, a violet coloration is observed. Acetic acid, and those substances which are converted into sugar by sulphuric acid, may be substituted for sugar. [Another test consists in placing a little of the suspected urine in a test-tube, and adding to it a few drops of tincture of iodine, when, if bile be present, the fluid becomes distinctly green].
Lead Tree. Dissolve 1 oz. of sugar of lead in a quart of distilled or filtered rain-water, adding a few drops of acetic acid. Filter, and put the clear solution into a decanter or bottle. Suspend in it a piece of zinc, and set it aside.
Tin Tree, Dissolve 3 drs, of chloride of tin in a pint and a half of water, with 10 or 15 drops of nitric acid; and suspend in it a rod of zinc.
It is usually made by dissolving black resin in oil of turpentine. Dr. Pereira states the proportion to he 5 fluid oz. of the oil to 16 oz. of resin; hut some makers put as much as 8, 10, or even 12 oz. of oil of turpentine to each pound of resin. [We have introduced this factitious preparation, because no genuine Venice (or larch) turpentine is rarely, if ever, to be obtained.]
Common turpentine, chiefly American, is distilled with water; the oil comes over with the water and is found floating on it. It is rectified by distilling it again with water. See Camphine and Solvents for India Rubber, for further modifications of this oil.
Oxide of iron, crocus, or jeweller's rouge.
A crystalline substance obtained from pine juice by Messrs. Tiemann and Harmann. It has been shown to be identical with the aromatic principle of vanilla.
These constitute a distinct branch of manufacture, and many of them can be advantageously or safely made only on the large scale on premises adapted for the purpose. A few of the most easily prepared and useful varnishes have been selected for insertion. For fuller information, see Dr. Ure's ' Dictionary of Arts, Dumas' 'Chimie appliquee aux Arts, etc.' Some practical information on this subject will be found in Mr. Red-wood's edition of Gray's ' Supplement,'and in the 49th vol. of the ' Transactions of the Society of Arts.'
Copal, fused and pulverized, 3 oz., sandarach 6 oz., mastic 8 oz., Venice turpentine, 2 1/2oz., methylated spirit a quart, powdered glass 3 oz. Mix the powdered glass and resins, and sift them; introduce them into a matrass with the spirit, and heat to boiling, constantly agitating till the gums are dissolved; then add the turpentine. Heat the varnish for half an hour, and when removed from the fire, agitate till cold.