S. N., of N. Y.—You should communicate with the Illinois Board of Agriculture in relation to the Bteam engine for agricultural purposes. We have no personal interest in the matter. J. T., of N. Y.—The cost of small knitting machines is about $100. Address Geo. Whipple, No. 23 William street, this city, regarding the purchase of them. E. W., of N. Y.—The constructing of a railroad break in the form of a shoe to be dropped in front of the wheel, for the purpose of taking the wheel from the track and resting the weight of the car upon the shoe, ia not new, nor has it proved practicable in operation. C. T. H., of N. Y.—You cannot prevent the magnetic current influencing a piece of soft iron when passing around it on a proper wire. Why do you ask such a question, when you can in an instant Btop the magnetic action by breaking the circuit between the magnet and the battery? J. B. M., of Me.—When you get your perpetual motion to work, we will get you a patent upon it, pay all the expenses of the application, and allow you to have the entire benefit which may be derived from the invention. We could not lay your matter before Congress, but perhaps the M. C. from your district might favor you, A. G., of La.—Carbureted hydrogen gas for illumination canbe made from wood in the same manner as it is made from coal; but it is not so good in quality an when the retorts are so made that the gas, after it is generated, is directedovera highly heated snrface before it goes into the cooler. You can make verygood gas from pine wood, however, by simply roasting the wood in a tight iron retort, and passing the gas therefrom through milk of lime and a water cooler, thence into a tight receiver for use. The apparatus is very simple. T. M., of N. Y., inquires how far a pound of lead will sink dropped into the Bea ? Ans.—It will Bink until it reaches thebottom, and that distance will depend of course upon the depth of the water. Wm. Cann, formerly of BlackRock, N. Y., is requested to give his present address to John M. Hartnett, of Wauconda, 111. J. V. Jenkins, of Detroit, Mich., the inventor of the sheep-shearing machine, illustrated on page 129 of the present volume of the Soi. AM., wishes to correspond with persons who would manufacture the machine or vend territorial rights. G. T., of —.Yonrfire alarm for hotels and houseB, consisting of an inflammable cord to be easily consumed by fire to detach the spring, so aB to set the alarm bell ringing, is not new. The same kind of an alarm was in operation some yeara ago in our office. S. B., of Pa.—Vulcanized india-rubber is verygood lor packing steam joints, but no oil must come in con. tact with it. If you use oil in your pipes you muat employ gasket and white lead packing. Pasteboard and white lead packing for joints also answer very well. C. C. S,, of Vt.—A heavy balance wheel placed in a frame upon platform scales will weigh as much while in motion as when at rest, and it will also bear as heavily upon its journal boxes when in motion as when at rest. E. S. A., of 111.—On page 357, Vol. 7, Soi. AM., you will find a very complete article on lithography. II. M., of Conn.—We are unacquainted with any reliable recipe-book relating to two such different arts as mixing paints and making soldera. In "Ure's Dictionary of the Arts," you will find considerable information, such as it is, on both subjects. H. H. P., of N. Y.—It will not affect the legality of your patent to sell machines before the patent is issued. II. C, of Mass.—We thank you for the nameB you send us, and will mail copieB of our paper to each. We are always pleased when subscribers can so strongly testify to the benefit gained from our paper. We thank you for your high testimonial. A. T. S., of Iowa.—Write to McAllister &Bro,, No. 728 Chestnut street, Philadelphia, regarding " dissolving vifwa" for exhibitions. J. A. B., of 111.—Your hoggish system of feeding hogs may be very profitable, but you must possess a stomach of infinite endurance, if you consider it palatable or possible. J. R., of La.—The Chinese sugarcane is cultivated in the same manner as Indian corn, and alcohol is distilled from its juice or sirup in the same manner and by the same processes as it is distilled from common molasses. J. R. S., ofN. Y.—We have examined your sketch of a hot air engine, and think it will operate, and run with considerable power, if you use plenty of fuel. Ericsson is now building some portable hot air engines for pumping water, at Delameter's works, this city, which are the most manageable and convenient engines for the purpose ever examined, You are mistaken in supposing that you can gain power by contracting the hot air in your engi UP as described in your letter. There is a gain obtained from expansion, but not contraction. G. II.,of Hiss.—Your communication is very interesting, but does not throw any light upon the subject of Berpcut charming. The suggestions you make on the strength of the anecdote are good, although we think tht.Te isa bit of the "hunter" in the story. M- R. A., of La.—There are engravings of gasworks that would suit you in the present number of our paper, and as to the roofing we have not any opinion for or against it, not being practically acquainted with its qualities. J. F. B., of Ohio.—-'Musical triangles"—those which we suppose, you mean,—are forged out of bar steel into the proper triangular form, and the three legB filed I round, then polished and tempered like any other piece ) of steel. F. DM of N. Y.—We are not acquainted with any HUD-'A stance which could be used m a Rubstitute for a hair brush that cannot be acted upon by sulphuric acid. What do you mean by " sheet links?" Money received at the Scientific American Office on account of Patent Office business, for the week ending Saturday, March 6,1868 :— L. P., of Del., $30; A. F. It, of N. Y., $30; C. W. H., of Mass., $25 ; A. H. G., of Ind., $25; B. C. V., of Ohio, $30; W. H. C, of 111, $30; F. N., of N. Y., $31; N. H. S., of 111., $10; J. A. B.,of La., $50; O. L. C, of 111., $25; I. B. J., of CaL, $10; L. R, of Mass., $5; A. E. L.,of Pa., $30; J. McN., of L. I., $30; W. B. D., of Conn., $25; W. B. Jr., of Mass., $20; C. W. &W. W. M., of-----,$20; J. C, of Ohio, $100; J. B.,ofN. Y., $30; J. L. R, ofS. C., $25; O. P. S., of Maine, $25; C. F., of N. J., $30; O. S., of N. Y., $25; C. M. L., of O., $30; J. B. McC, of Ky., $30; F. B., of N. Y, $15; S. D. C., of Wis., $100; M. E., of Ohio, $25; W. Z., of Pa., $25; B. &F, OfN. J., $10; B. R M., of Fla., $30; G, &G., of Pa., $30 ; J.V.S., of Mass., $35; J. F. E., of Conn., $25; A. &Bro., of Conn., $25; J. H., ofN. Y., $25; B. K., of Pa., $25 ; W. H. M., of Iowa, $30; F. S., of Pa., $25; A. A., of L. I., $25; A. H.,of N. J.,$25; T. W., of L. I, $25; J. Mol, ofN. Y, $25. Specifications and dra wings belonging to parties with the following initials ha ve been forwarded to the Patent Office during the week ending Saturday, March 6,1858 :— A. H. G., of Ind.; C. W. H., of Mass.; J. B. J., of Cal.; A. A.,of N. Y.; A. H.,of N. J.; W. R D., of Conn. ; A. E. L., of Pa.; T. W., of L. L ; G. T., of N. Y. ; F. N., of L. L ; I. L. E., of S. C.; J. Mel., of N. Y.; R B., of Ohio; M. E., of Ohio; W. Z., of Pa.; J. F. E., of Conn.; S. &J., of Ky.; J. F. A., of N. Y. ; A. &Bro's. of Conn.; F. S.. of Pa.; W. C, of Ind. Terms of Advertising Twenty-five cents per line each insertion. We re-pectfully request that our patrons will make their advertisements as short as possible. Engravings oanEE* be admitted into the advertising columns. *#* All advertisements must be paid for before inserting.