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, stra.s.s 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 ma.s.s 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 coa.r.s.eness 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.

W. H. B., of Va.--Ice can be made by compressing air, and, after it has radiated its heat, allowing it to extract the heat of water with which it is brought into contact. The temperature of air at 59 Fah., would be raised, by compressing the air to one fourth its original volume, to 317 Fah; and the air would radiate and absorb again, in expanding, about 190 units of heat.

E. T. H., of Ga.--The friable sandstone, a specimen of which you send us, may, we think, be rendered firmer by soaking it in a solution of silicate of soda, and allowing it to stand till dry.

J. A. V., of Ohio.--The use of steam expansively, by means of cut-off appliances, enables the expansive force of the steam to be utilized, which cannot be done when the pressure is maintained at one standard, and steam admitted through the fall stroke. It takes no more power to do a given amount of work in one case than in the other, but more boiler capacity, and more fuel, as the working power of the steam is more economically applied when the cut-off is used.

Geo. F. R., of Ohio.--Type metal is composed of 3 parts lead and 1 part antimony for smallest, hardest, and most brittle types; 4 of lead and 1 of antimony for next grade; 5 of lead and 1 of antimony for medium sizes; 6 of lead and 1 of antimony for larger types; and 7 of lead and 1 of antimony for the largest.

E. J. M., of Texas.--The term "power of a boiler" means its evaporating power, and in that sense is proper. If its evaporative power be sufficient to perform a given amount of work, it is proper to estimate that work in horse power. Water can not be pumped out of a pipe from which atmospheric air is excluded. A pipe driven into a soil impervious to air, can never yield water unless the water is forced up by hydraulic power, as in the artesian system.

A. P. Y., of N. Y.--You will find descriptions of iron enamelling processes, on pages 297 and 408, Vol. XII. of this journal. It can be done in colors. See Ure's "Dictionary of Arts and Manufactures."

H. C., of Pa.--We do not think increasing the size of the journals of your car axles from 2 inches to 6 inches diameter, would make them run lighter.

H. H. A., of N. Y.--The lining up of a beam engine, in a vessel, is a process for which no definite mode of procedure is exclusively applicable. It is an operation to which common sense and judgment must be brought, and for which each engineer must be a law unto himself.

J. S., of Va.--The use of horizontal propellers to force balloons up or down is not a new suggestion. It has been tried, but, we believe, without much practical success.

J. T .S., of N. Y.--You will find further information on the subject of transmitting power by compressed air, in our editorial columns of last week.

APPLICATIONS FOR EXTENSION OF PATENTS.

HARVESTERS.--William T. B. Read, Chicago, Ill., has pet.i.tioned for an extension of the above patent. Day of hearing, May 17, 1871.

MODE OF FASTENING SHEET METAL ON ROOFS, ETC.--Asa Johnson, Brooklyn, N. Y., has pet.i.tioned for an extension of the above patent. Day of hearing, May 3, 1871.

METHOD OF PRINTING IN COLORS.--Rosalie Croome, Brooklyn, N. Y., has pet.i.tioned for an extension of the above patent. Day of hearing, May 3, 1871.

MACHINERY FOR COMPRESSING GASEOUS BODIES.--William A. Royce, Newburgh, N. Y., has pet.i.tioned for an extension of the above patent. Day of hearing, May 10, 1871.

PLOWS.--John S. Hall, Pittsburgh, Pa., has pet.i.tioned for an extension of the above patent. Day of hearing, May 17, 1871.

CARRIAGE WHEELS.--James D. Sarven, New Haven, Conn., has pet.i.tioned for an extension of the above patent. Day of hearing May 24, 1871.

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