264. _Diamond Cement._--Diamond Cement, for glass or china, is made by dissolving a quarter of an ounce of isinglass in water, by boiling it to the consistence of cream. Add a table-spoonful of spirits of wine. Use warm. 265. _Cement for attaching Metal to Glass or Porcelain._--Take two ounces of a thick solution of glue, and mix with one ounce of linseed oil varnish, or three-quarters of an ounce of Venice turpentine. Boil together, agitating them until thoroughly mixed. The pieces to be cemented should be left untouched, after having been united, for forty-eight or sixty hours. 266. _To mend Tortoise-Shell._--To mend tortoise-shell, bring the edges of the pieces to fit each other, observing to give the same inclination of grain to each; then secure them in a piece of paper, and place them between hot irons or pincers; apply pressure, and let them cool. Take care that the heat is not too great, or it will burn the shell. 267. _To clean Gold Chains, &c._--Make a lather of soap and water; boil the chain in it for a few minutes, and immediately on taking it out, lay it in magnesia powder which has been heated by the fire; when dry, rub it with flannel; if embossed, use a brush. _Or:_--Wash it well in soap and water, and put it while wet into a bag with some fresh, clean bran; shake it well, and in a few minutes it will be found perfectly clean. 268. _To restore Pearls._--Soak them in hot water in which bran has been boiled, with a little salt of tartar and alum, and rub them gently between the hands; rinse them in lukewarm water, and lay them out to dry. To preserve the color of pearls, keep them in dry common magnesia, instead of the cotton-wool used in jewel-cases, and they will never lose their brilliance. 269. _To clean Gold or Silver Lace._--Rub it gently with cotton wool, or a soft brush dipped in spirits of wine, taking care not to injure the silk beneath. 270. _To clean Gold and Silver Lace._--Sew the lace in linen cloth, and boil it in a pint of water, and two ounces of soap; and then wash the lace in water. 271. _To improve Gilding._--Mix one gill of water, two ounces of purified nitre, one ounce of alum and one ounce of common salt. Lay this over gilt articles with a brush, and their color will be much improved. 272. _Incombustible Varnish for Wood._--Equal parts of alum and isinglass, dissolved and mixed, applied to wood, prevents it from burning. Liquids can be boiled in a wooden vessel on a common fire, if this varnish be applied to it. The wood chars sometimes, but does not flame. 273. _Cement for Iron Flues._--Common salt and sifted wood-ashes in equal parts, made into a paste with water, is a very good cement for iron flues, and may be applied when the flue is hot or cold. Iron filings and vinegar will do almost as well, or rather iron filings moistened with diluted muriatic acid. These are generally used for filling up the space between cylinders.