These consist of vegetable colours in combination with alumina. Alum is usually added to an infusion or decoction of the colouring ingredient, and afterwards potash added, which throws down the colouring matter combined with alumina. Some of the lakes are noticed under Pigments.
Dissolve 4 oz. of citric acid in 3 pints of water, with 8 drops of essence of lemon, rubbed with the acid, or dissolved in a little spirit. After standing ing a few days, filter it, and preserve it in well-closed bottles.
Procure a piece of thin platinum wire, and twine it once or twice round a pin's point, so as to form a minute ring with a handle to it. Break up a piece of flint glass into fragments a little larger than a mustard seed; place one of these pieces on the ring of wire, and hold it in the point of the flame of a candle or gas-light. The glass will melt and assume a complete lens-like or globular form. Let it cool gradually, and keep it for mounting. Others are to be made in the same manner; and if the operation be carefully conducted, but very few will be imperfect. The smaller the drop melted, the higher in general will be its magnifying power. It may be mounted by placing it between two pieces of brass which have corresponding circular holes cut in them of such a size as to hold the edge of the lens. They are then to be cemented together. - Francis.
- Heat in a copper boiler 50 gallons of linseed oil to 280° F.; add 2 1/2 lbs. of calcined white vitriol, and keep the oil at the above temperature for half an hour; then remove it from the fire, and in 24 hours decant the clear oil, which should stand for a few weeks before it is used, for varnish.
(Wiles' Patent.) In 236 gallons of oil pour 6 lbs. of oil of vitriol, and stir them together for 3 hours; then add 6 lbs. of fullers' earth, well mixed with 14 lbs. of hot lime, and stir for 3 hours. Put the oil into a copper boiler, with an equal quantity of water, and boil for 3 hours; then extinguish the fire, and when the materials are cold draw off the water, and let the oil stand to settle for a few weeks before using.
See Anti-Attrition. The French compound term Liard is thus made: - Into 50 parts of finest rape oil put 1 part of caoutchouc cut small, and apply heat until it is nearly all dissolved.
Mankettrtck's; Lubricating Compound consists of caoutchouc (dissolved in spirit of turpentine) 4 lbs. common soda 10 lbs., glue 1 lb., oil 10 gallons, water 10 gallons. Dissolve the soda and glue in the water by heat, then add the oil, and lastly the caoutchouc, stirring them until perfectly incorporated.
See Matches, further on.
Nearly fill a bottle with olive or almond oil, and heat it in a water-bath. Drop into it small slices of phosphorus so long as it is dissolved. Let the solution cool, and pour off the oil from the undissolved phosphorus into clean dry phials, which should not be quite filled. When uncorked they emit light.