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 deg. Fah., would be raised, by compressing the air to one fourth its original volume, to 317 deg. 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 21/2 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 petitioned for an extension of the above patent. Day of hearing, May 17, 1871.