Drying Oils and Dryers. All the fixed oils have an attraction more or less powerful for oxygen; and, by exposure to the air, they either become hard and resinous or sour and rancid. Those which exhibit the first property in a marked degree, as the oils of linseed, poppy, rape, and walnut, are called drying oils, and are used as vehicles for colors in painting. The drying property of oils is greatly increased by boiling them, either alone or with litharge, sugar of lead, etc., when the product forms the boiled oil or drying oil of commerce. The litharge and sulphate of lead employed for this purpose, may be again used, after washing them in hot water, to remove adhering mucilage. "When paints are mixed with raw oil, as is frequently the case in house painting, the drying quality is obtained by the addition of compositions called dryers. These are generally made from Japan varnish, sugar of lead, litharge, etc., and are necessary in such paints as are preferably prepared without boiled oil.

2727. Dark Colored Boiled Oil

2727.    Dark Colored Boiled Oil. Simmer with frequent stirring, 1 gallon of linseed oil, with 3/4 pound powdered litharge, until a skin begins to form; then remove the scum, and when it has become cold and has settled, decant the clear portions. This is for house painters' use.

2728. Pale Boiled Oil

2728.     Pale Boiled Oil. Boil 1 quart linseed oil, and 2 ounces powdered white vitriol (sulphate of zinc), with 1 quart water, until the water has all evaporated; settle and decant as in the last receipt.

2729. Very Pale Drying Oil

2729.    Very Pale Drying Oil. Mix 2 ounces finely powdered litharge, or dry sulphate of lead, with 1 pint pale linseed or nut oil; agitate frequently for 10 days, then set the bottle in the sun or in a warm place to settle. When clear, decant it.

2730. Colorless Drying Oil for Paint

2730.    Colorless Drying Oil for Paint. Take 5 gallons water, heat it to the boiling point in a vessel holding 15 gallons; when about to boil add 5 gallons linseed oil and 1 pound red lead. Keep it constantly boiling and stirred up for 2 hours over a slow fire. If not constantly stirred the lead will sink to the bottom and cause the oil to spatter. It is then taken from the fire and left to settle, when it will be found that the oil is clear and colorless.

2731. Mulder's Colorless Drying Oil

2731.    Mulder's Colorless Drying Oil. Boil linseed oil for two hours with 3 per cent, of red lead; filter it, and expose it to the sunshine in large shallow vessels, with a glass covering, frequently removing the cover to renew the air.

2732. To Make Boiled Oil Clear and Bright

2732.    To Make Boiled Oil Clear and Bright. There is often a difficulty in obtaining the oils bright after boiling or heating them with the lead solutions. The best way on a small scale is either to filter the boiled oil through coarse woolen filtering paper, or to expose it in a bottle for some time to the sun or in a warm place. In larger quantities, the oil may be filtered through Canton flannel bags.