H. R., of Iowa.—Ths oreide of gold is described on page '508, of our last volume. The hands of watches are colored red by a simple lac varnish tinged with carmine. II. W., ofVt—The increased quantity of hydrotfra given off at the negative pole of a battery under Avjittr, by attaching a piece of zinc to it, is duo, we think, to the decomposition of the zinc itself by the water ; IV. ?? oxygen of the water unites with the zinc, and the hydrogen escape?. C. C, Jr., of Mass.—If you write on paper with a solution of the muriate of cobalt it, it will become invisible until it is exposed to heat before a fire. II. E. O., of N. Y.—The subject " In what part of the earth is attraction greatest ?" is more speculative than instructive. We do not question the correctness of your views. R. A. R., of Maine.—We are happy to answer your question, and hope that all who are " too poor to buy knowledge in bound volumes " will apply to us, and they shall have it gratis. Shellac is procured from a tree in the East Indies, out of which it exudes as a resinous gum. It is collected and heated in linen bags, through which it drops on to flat plates, and these are broken up as we import them. Its chief use is in the manufacture of sealing wax. D., of N. Y—A paint of boiled linseed oil and litharge is used tor protecting wire rope and the hulls of iron ships. It is the best coating, we understand, that has yet been applied for this purpose. G. II.. of Ohio.—If you wish your engraving sent to you by mail, please remit fifty cents in- stamps?, to prepay the postage. W. L., of Md.—A patent cannot be secured for making chimney flues of enameled or glazed earthenware. Flues of this character have been used. L. II., of Mass.—It is not new to secure hubs to axles by means of a plate screwed to the back end of the hub, with flanges on the axle running in a recess. There are models of the same thing now in the Patent Office. E. W. C, of Mich—It has been held that a contract may be legally made to convey a future invention, as well as a part of one, or for any improvement or a part of one; and a bill in equity will compel the performance of a contract made under these conditions. C. D., of C. W.—We are of opinion that you can procure a machine for making drain tiles of Emery Brother, Albany, N. Y. C. L., of Conn.—You must start right in your calculations, else they will all end in confusion and disap-lK)intment. There is no power gained by a lever—it is only a means of transmitting power; a lever in itse has no more power than a cobble-stone. In regard to a water wheel, we should prefer a 40-foot wheel, with 12-foot buckets, to a 20-foot wheel with 21-foot buckets, so as to obtain a more free reception and discharge of the water, but not on account of any gain in leverage. K. P., of K. I.—We cannot undertake to give opinions upon questions of infringement. You must consult some attorney in your own place. A. R., of Cal.—We have entered your name with Mr. Locke, in our subscription book's, for five years each, and mailed to both a bound volume (XII) to balance your account. D. P. F.,of Conn.—In No. 32, Vol. I, Scientific American, you will find an engraving of an apparatus for ky-anizing timber, F. P. N., of Cal.—You have got our old friend Porters plan for extending telegraph wires across rivers, and from mountain to mountain across valleys, by means of small balloons inflated with hydrogen gas. The plan is very good in theory, but in practice you would have tv,ror more difficulties to encounter ; first, you could not retain the gas in the bags; and secondly, the wind would play the mischief with the bags if they could be made to hold the gas. G. W. C, of Ohio, say* .-—"There has been quite a controversy here* among some of the knowing ones, and to settle the matter, they have concluded to leave it to your decision. The circumstances are these .'—Suppose A receives a patent for a certain machine, and sells the undivided one-half of his said patent to C ; then the said A (the patentee) makes an improvement on his patent, and gets it patented. Now the question is, whether the said C has an equal interest In said improvement with the patentee?" Answer.—Unless the original assignment of one-half of the patent to C particularly specified that he should be entitled to an equal interest in any improvement which A might subsequently make in the machine, C would have no interest in it whatever. Condit Vaughan, of Exchangevillc, Pa,., wish to purchase the best machine knovm for turning carriage spokes. D. R., of Wis.—To enable us to get up a nice engraving of you saw-mill, it will be necessary for you to furnish us with a model to take the views from. The expense would be $15. We cannot recommend to you any agency for the selling of your patent that we know of. Our observation has taught us that an inventor can sell his own invention better than a second party, unless the agent he may appoint makes it his sole business to operate with one patent only. Most agencies who make it a business to sell patents take so many inventions in hand to dispose of, that their attention is divided among a dozen or more different interests, and thus they seldom accomplish anything. L. L., of Pa.—You can stain a blackboard with a strong solution of logwood and copperas, applied hot with a sponge. After it is dry, give it a coat of paint made of boiled linseed oil and lampblack, which you must allow to dry perfectly before it is used. In this manner you will make an excellent blackboard. If you wish to make one on which to write with a light-colored I slate pencil, mix some fine emery or ground giasa with v-Aiir mint. W. R, of Ohio, inquires :—"If, in case a patentee assigns a portion of territory to A, and another portion to B, and A takes out a re-issue, can B, on suing for infringement, have the benefit of said re-issue ?" The object of the re-issue of a patent is to correct some mistake or error which has arisen trom inadvertence. It is done by surrendering the old patent and obtaining a new or amended ono. The assignee has a perfect right to his interest under the re-issued patent, and his right ceases only when the patent expires. The assignee would have no legal interest in the patent if extended beyond its oi'iginal date. 15. F., of Ind.—We are not acquainted with any other proccsri for preserving eggs than that of immersing them in lime water in tubs. The slacked lime should be ;?! iq-ccl in the water until it is nearly as thick as cream, and the eggs then laid gently in it, and covered entirely with the water. We have seen eggs preserved fresh in this manner for six months; but while they are suitable for frying with ham, or for making pastry, they have a lime taste when simply boiled. Z. E. C, of Conn.—There is no simple process for coloring furs black or brown. They are colored in the same manner, and with the very same substances, as wool and skins, but they require several dips, and the temperature of the liquors must be low. Logwood, sumac, and the sulphate of iron will color black; camwood, fustic and logwood will color brown. W. G., of Mass.—Oil will dissolve gum shellac, which ia not suitable to use for cement in an oil lamp. If you use some dissolved glue and litharge with the plaster of Paris, we think you will obtain a cement suitable for your purpose. W. W. McC, of Ala.—Bourne's Catechism of the Steam Engine can be had for $1, of Appleton Co., of this city. The American Engineer is defunct. A. C K, of Mass.—Your case will be brought up in a few days, for examination by one of our firm, who is in Washington, and a report upon the prospect of success sent to you. Your remittance of $4 pays for the advertisement in full. R. S., of-----.—The divining rod is an exhausted subject. You state that a straight rod held between the fingers is just as good as a crooked branch held between the hands for pointing to water underneath the surface. We agree with you; the one, we think, is just as good as the other. But that either of them is reliable, or will twitch the hand when passing over a subterranean stream of water, we do not believe. E. P., of Ohio.—There is no existing patent on the counting-house ruler, having a parallel roller which extends its whole length, and revolves on pins in metal plates at each end. This patent was granted in 1832 to James Carrington, of Conn., and is now public property. This ruler, as originally patented, had two rollers ; they are now usually made with but one. You can make as many as you please. C. C. II., of N. Y.—Any kind of oak wood used in steam boilers tends to prevent incrustations. You can stop your hands from sweating, to enable you to play on the violin, by washing them in a solution of alum, and allow them t dry without wiping off. But we advise you not tod hism order to be skillful on the instrument, because it is not safe to stop the pores of any part of the body from throwing off their natural perspiration. W F. D., of Va.—Your method of rapid multiplication appears to bo similar to that practiced by Peter Deshong, a great calculator, who lived in this city about nine years ago. So much has been done in the way of making arithmetical rules for rapid multiplication, that it is difficult to say what is new and what is old. G. C, of N. Y.—A strong solution of fine isinglasa, in which a very little French chalk has been intimately mixed, will, if placed between two pieces of mother-of-pearl, and allowed to dry, form an artificial mother-of-pearl, possessed of a surface displaying all the varying hues of the natural substance. The artificial mother-of-pearl manufactured in Paris, is formed of a paste, the principal ingredient ot which is a solution of fiahes1 scales, but we are not acquainted with the minutae of the process. J. M., of Pa.—We do not think that the governments of either the United States or Great Britain have ever offered a reward for the discovery of the cause and prevention of the potato rot; neither can we believe that you have made this discovery, though we certainly hope you have. The United States Agricultural Society is the proper medium for you to look for compensation— not to Congress. E. R., of Mass.—By melting and cooling lead several times in succession it becomes somewhat harder. To form an alloy of lead and zinc they should be melted separately, then mixed together in a molten state, and carefully stirred for a few minutes. This operation must be conducted with great caution; the zinc should be poured very slowly among the molten lead, or it will be liable to spatter out. R. M., of C. W.—Water lime is hydraulic cement. It is the best thing you can use to form a concrete foundation lor a house in a damp sitution. It is employed for the lower stratum of foundations, and for the inside and outside plaster of brick walls under ground, in some localities, and answers an excellent purpose; but the interior roys of the bricks are united with common mortar. Gutta percha tubes answer very well for conveying water, if made strong, but they are liable to be eaten by rats ; therefore we do not recommend theii use in exposed situations. If you do not wish to use lead pipes, use cast iron or wood. M. C, of R. I.—A paper for covering buildings has been made by taking finely-ground coal and sulphur, and intimately mixing them with pulp. By passing the sheet between heated rollers, the sulphur is melted, and thus the paper is rendered impervious to water. We cannot advise you to use it; better get prepared canvas. A. F., of Oregon—Addison Everett, of Middlefield, Mass., secured a patent some years since for a lathe for turning hollpw woodenware. Since that time, we believe no patent has been taken on machines of this class. U. U. G., of Pa.—We do not know where you can obtain recipes for making six gallons of distilled spirits from one bushel of malt; the larger portion of such a production must be the water. J. H. P., of Me.—In the manufacture of potato-brandy, the crude spirit is found to be contaminated with an acid volatile oil, called "fusel oil," which is extremely difficult to separate in a complete manner. Towards the end of the distillation it, passes over in considerable quantity, when it may be collected by washing the spirit away with water. It is this substance that gives the peculiar pear-like flavor to many spirits; and it is much used by confectioners to flavor candies. It is a most deadly poison, and should be used with caution. When possible, it is better to re-distill the liquor than to let it remain in, as its effects, however slow, are very sure. Money received at the Scientific American Office on account of Patent Office business, for the weekending Saturday, December 5, 1857 :— H. F. B., of 111., $30 ? R. L., of Wis., $13 ; H. F. S., of Mich., $25; JK. B., of N. Y., $10; P. C. M., of 111., $37 ; G. S., ofVt., $25; V. R. D., of 111., $25; J. L., of Tenn., $30; W. W. D., of Cal.. $50; J. G., Jr., of R. I., $32 ; J. O., of Pa., $25 ; L. C. W., of N. C, $30 ; G. P. K, Jr., of Ind., $30 ; II. U., of N. Y., $45; E. E., of 111., $25 ; L. K, of N. Y., $30 : A. S.. of N. Y., $30 ; E. C, of Mass., $100; A. B., of N. Y., $55. Specifications and drawings belonging to parties with the following initials have been forwarded to the Patent Office during the week ending Saturday, December 5,1857:— J. V. J., of Mich.; D. E. of Ohio ; J. E. H., of N. Y.: D. W of L. I.; D. G., of Pa.; W. M., cfKy.; 8. C, of S. C.; B. II., of 111.; H. T. S., of R. I. ; II. T. S., of Mich.; G. S., of Vt. ; J. G. Jr., of R. I. ; A. S., of N. Y. ; D. B., of K. I., (2 cases)fc H. U., of N.Y.; E. E., of 111.; J. O.,of Pa. Literary Notices BLACXWOOD'B MAGAZINE—This favorite monthly, re-publislied by Messrs. Leonard Scott Co., 54 Gold st., this city, contains the conclusion of the interesting story, "Janet's Repentance,11 " Notes on the Isthmus of Panama," and several other excellent articles and stories. The number for this month is a good one. SOUTHERN AID SOCIETY RRPOKT—We have received the Fourth Annual Report of this excellent Christian Society. It has received and appropriated about $52,00C since its operations began, and judging from the Treasurer's Report, the Society is getting a warm hold on the Christian community. The object of the Society is to diffuse gospel truth in the southern and southwestern States. The Treasurer of the Society is Gerard Hallock, Esq., Editor of the Journal of Commerce, in this city. To Our Subscribers RECEIPTS—When money is paid at the office for subscriptions, a receipt for it will always be given ; but when subscribers remit their money by mail, they may consider the arrival of the first paper a bonajide acknowledgment of the receipt of their funds. The Post Office law does not allow publishers to enclose receipts in the paper. Terms of Advertising Twenty-five cents per line each insertion. We respectfully request that our patrons will make their advertisements as short as possible. Engravings cannot be admitted into the advertising columns. * All advertisements must be paid for before inserting.