Take of spirits of wine, 1 pint; divide it into four parts; mix one part with half an ounce of gum mastic, in a bottle by itself; one part of spirits and half an ounce of gum sandrac in another bottle; and one part of spirits and half an ounce of the whitest part of gum benjamin; mix and temper them to your mind; if too thick, add spirits; if too thin, some mastic; if too soft, some sandrac or benjamin. When you use it, warm the silvered plate before the fire, and with a flat camel-hair pencil stroke it over till no white streaks appear; which will preserve the silvering for many years. 543. VARNISH FOR BALLOONS Take some linseed oil, rendered drying by boiling it with 2 ozs. of sugar of lead and 3 ozs. of litharge for every pint of oil till they are dissolved, which may be in half an hour. Then put 1 lb. of birdlime and half a pint of the drying oil into an iron or copper vessel, whose capacity should equal about a gallon, and let it boil very gently over a slow charcoal fire, till the birdlime ceases to crackle, which will be in about half or three-quarters of an hour; then pour upon it 2-1/2 pints more of the drying oil, and let it boil about an hour longer, stirring it frequently with an iron or wooden spatula. As the varnish, whilst boiling, and especially when nearly ready, swells very much, care should be taken to remove, in those cases, the pot from the fire, and to replace it when the varnish subsides; otherwise, it will boil over. Whilst the stuff is boiling, the operator should occasionally examine whether it has boiled enough , which may be known by observing whether, when rubbed between two knives, which are then to be separated from one another, the varnish forms threads between them, as it must then be removed from the fire. When nearly cool, add about an equal quantity of oil of turpentine. In using the varnish, the stuff must be stretched, and the varnish applied lukewarm. In 24 hours it will dry. As the elastic resin, known by the name of Indian rubber, has been much extolled for a varnish for balloons, the following method of making it, as practiced by M. Blanchard, may not prove unacceptable: dissolve elastic resin cut small in five times its weight of rectified essential oil of turpentine, by keeping them some days together. Then pour 1 oz. of this solution in 8 ozs. of drying linseed oil for a few minutes; strain the solution, and use it warm. 544. TO PREPARE RENNET TO TURN MILK Take out the stomach of a calf as soon as killed, and scour it inside and out with salt; after it is cleared of the curd always found in it, let it drain a few hours, then sew it up with two good handsful of salt in it, or stretch it well salted on a stick, or keep it in the salt wet; and when wanted soak it a little in fresh water, and repeat the same when again required. 545. TO MAKE CHEESE