These prints should be washed and kept dry for future use. A variety of figures may be produced with the same print, by varying the colours. 115. TO MAKE ELASTIC BLACKING FOR LEATHER.--Dilute one ounce of gum-asphaltum with a pint of spirits of turpentine, in the manner described at 51;--put this into a flask, and add one ounce of gum-elastic cut into very small pieces, and half an ounce of gum-shellac previously reduced to powder. Suspend the flask unstopped over a fire of charcoal, or set it in a sand bath where it may boil gently till the quantity is reduced to a gill; then strain it through a flannel, and when nearly cold, bottle and cork it. The leather should be thoroughly blackened with some liquid blacking and waxed over slightly with bees-wax before the elastic blacking is applied. If the blacking should be too thick, it may again be diluted with spirits of turpentine. It should be warmed when applied, and the work may require several coats, and a considerable time for each to dry. Any of the above mentioned gums may also be dissolved in sulphuric ether, and thus produce a fine drying varnish, but the preparation is much more difficult as the volatile nature of the ether will not admit of much heat, whereby to facilitate the solution. 116. SUNDRY EXPERIMENTS.--Rub together a little dry powdered alum, and acetate of lead; both will become fluid. To a saturated solution of muriate of lime, add a saturated solution of sub-carbonate of potass, (both transparent liquids,) the mixture will be nearly solid. Rub together a little pure white calomel (sublimed mercury) and pure white ammonia (being moistened;) both will become intensely black. Fill a flask nearly half full of water, and apply heat till it boils; take it from the fire and (when it has done boiling) cork it; pour cold water upon the flask, and the water inside will re-commence boiling. Fill a glass with water, and lay a piece of paper upon the top of it; place your hand upon the paper, and invert the glass; the hand may be removed and the glass may be suspended in that position by a thread, and the water will not be spilled. Expose a piece of ice to the action of (cold) muriatic gas; the ice will be instantly melted. Drop a piece of phosphuret of lime, into a glass of water; bubbles will soon rise, and on reaching the surface of the water will spontaneously explode. Apply the end of a roll of brimstone to a hot bar of iron; a part of the iron will be instantly melted, and will fall. Write with diluted sulphuric acid, on paper that has been coloured brown by a mixture of sulphate of iron, and infusion of galls; the writing will be white. Moisten the under lip, and lay upon it a piece of silver money, (not less than a twenty cent piece) with the edge of it beneath the tongue; lay a piece of zinc, of nearly an equal size, upon the tongue, and bring the edges of the pieces of metal into contact; you will instantly drop the money. _Appendix._