MIXING METALS.--All the hard gray American charcoal iron, of which car wheels and all such work are made, requires more heat and a longer time to melt than soft iron, especially Scotch pig, which is the most fluid and the easiest to melt of any iron. Consequently, unless the melter exercises good judgment in charging, the Scotch pig will melt and run off before the car-wheel iron is melted. If G. H. P. be particular in the quality and strength of his iron, he will make better results by using soft American charcoal pig, with old car-wheel iron. It will make stronger castings, mix better, and melt more uniformly; but he should always recollect in charging his furnace that soft iron will melt before hard in the same position, in the cupola. I also think he had better use a larger proportion of soft pig, as every time cast iron is melted it becomes harder, so much so that iron which can be filed and turned with ease, when re-cast will often be found too hard to work.--J. T., of N. Y. HARDENING TALLOW.--If E. H. H. will use one pound of alum for every five pounds of tallow, his candles will be as hard and white as wax. The alum must be dissolved in water, then put in the tallow, and stirred until they are both melted together, and run in molds.--F. O. H. L. L., of N. Y.--According to Ure, strass is made as follows: 8 ounces of pure rock crystal or flint, in powder, mixed with 4 ounces of salt of tartar, are to be baked and left to cool. The mixture is then poured into hot water, and treated with dilute nitric acid till it ceases to effervesce, and the "frit" is then washed in water till the water comes off tasteless. The frit is then dried, and mixed with 12 ounces of white lead, and this last mixture reduced to fine powder, and washed with distilled water; 1 ounce of calcined borax is now added to every 12 ounces of the mixture, the whole rubbed together in a porcelain mortar, melted in a clean crucible, and poured out into pure cold water. This melting and pouring into water must be done three times, using a clean, new crucible each time. The third frit is pulverized, five drachms of niter added, and then melted for the last time, when a clean, beautiful white crystal mass results. C. M. S., of Wis.--There are no precise proportions observed in making the coal-tar and gravel walks of which you speak. The aim is to saturate the gravel with the hot tar without surplus. The interstices of the gravel are simply to be filled, and the amount required to do this depends wholly upon the coarseness or fineness of the gravel employed. W. P. T., of Ohio.--Two teams of horses, of equal strength, pulling against each other, by means of a rope, would create the same tension in the rope, as one of the teams drawing against an immovable object.