F. W. F., of C. 'V.— \Vi1sen's process of Hrender_ ing" lard consists in subjecting it to the action of steam in a strong iron boiler containing perforated iron shelves. The pressure of the steam is maintained at 50 pounds on the square inch for some hours. 'rhe water of the condensed steam is run off at the bottom, and the rendered lard is obtained floating on the top. The steam is carried by a pipe from the steam uoiler into the trying cylinder or kettle. C. E. S., of Minn.—The best paint for steam boilers with which we arc acqnainted, is compodcd of equal parts of black lead and red oxyd of iron, mixed with boiled linseed oil. E. W., of Conn.—Kerosene, or coal oil, is not generally understood to bo explosive. All explosive burning fluids contain alcohol. Such fluids must be vaporized, and mixed with eight volumes of air before they will explode when ignited. Some burning fluids sold under the name of kerosene oil may contain alcohol, but they arc a frand upon the community. J. J. 0'8., of Tenn.—Some perdons who have bee"n rendered insensible by u weak stroke of lightning hav\ recovered by a plentiful application of cold water; but a powerful stroke of lightning uestroys life. 'Vc have never known a case of poisoning by prussic acid iii which the acetate of potash and comlllon salt in solution proved a perfect antidote. L. A. 0., of N. Y.--Xot a particle of proof has ever been adduced to show tha.t nitric acid produced by lightning during thunder storms id the Callse of sweet milk becoming sour. B. N. B., of Pa.—Cast iron is bronzed with a variiisli and common bronze powder, which yon can purchase at nny llaint store. W. D. B., of Pa. —To describe to you the whole process of treating catechu, from tile time it leaves the forest till manufactured into all kinds of articles for which it is used, would require too much Hpnce for our con'espondence column. Articles on Ihis suhject }wxc been Ilubl hed in the Scr. AM. from time to time f o the last ten years. \Ve would refer you to back volumes. L. 'V. N., of Mu83.—The government fee for nn extension of a patent is $40. J. A., of ^Iasd.— \Ye have examined the dra,yings and specification of your cable-laying apparatug in Newton's Journd, and find that it differs e83entially from Mr. Bcrdau'a or the apparatus on board the Agamemnon and Niagara, inasmuch as your paying-out rollers and thdr carriage move altogether with an increased strain, which seems to make it less simple and eilective. H. C., of N. Y.—You can procure i\ mill udapted to grinding bones from James BogarduE, tllis city. E. II., of Mass—If you. 8tecl1 yonr hoops in a liquor of the sulphate of copper, made by dissolving 1 pound of the sulphate to every 30 gallous of water, they will be protected against dry rot, aud from the attack of worlDS. H. P. M., of N. Y.—Your communication i6 receivcd , and wIll appear in our next numuer. J. G., of M.- We shall be glad 10 examine the model of your proposed improvement in plows. We quite agree with you that perfection has not been reached even in the old familiar subject of plows. H. W. D., of M",..—We do not believe any of the railroad companies in this city have ever offered a prize for a brake to be used on their small cars. B. C. Morrison, of St. Anthony, Minn., wishes to pnrchase a machine for turning aud pointing common pickets for fences. B. S, of N. Y.—You in'lllire if h a coil spring used for the purpose of straining snw* cnn be patented." 'Ye reply, it cannot; such springs have been used for this purpose. J. R, of Ill.—For auch information as you want in reference to the tl1nnage of American and Britidh yes-scls, address editors of Hunt's Merchants' Magazine. We cannot furnish it. B. C. M., of Minn.—Some nssert thut the rcaoon why a bar of cold pig iron is kept afloat in the molten metal id in consequence of an electric repulsion between the molten and solid mctal. Others asaert that this occurs because the metal id heavier in R fluid than in a solid state. It is difficult to determine which of these tw:o theories is con-ect. J. B. L., of Pa.—Making the knobs for fastening carriage curtains of wood, instead of silver, or other metal, i8 not new. If SUGII a change of material ,vere'sels.-new it would not be patentt\ble, as its adoption does not either involve iuvEntion, or produce the new and beneficial result required in tile few cases where the simple change of material justifies the issue or a pateut. H. W., of Pa.—The application of a known device to accomplish a well-known result, in the form you tmggest, is not, of course, patentable. Money recei,ed at the Scientific Amcrican Office on account of Patcnt Office business, for the weekending Saturday, June 19,1858 :— J. H. W., of Wis., $30 ; B. Du F., of Wis., $25; S. G., of N. Y., $28; J. D. F., of Mass., $30; P. D., of N. Y., $30 ; J. D. T., of Ohio, $25 ; 1'. B., of Vt., $55; H. K., of Ind., $30 ; J. H., of Mass., $25; P. T. tt, of IlI., $30; G. II., of N. Y.,$3u; A. J. C., of Tenn., $25 ; W. R. W., of Mass., $30; O. R. B., of N. Y., $10; J. N. L., of N. Y.,$30; A. A., of Vt., $30 ; L. A. G., of Mass., $27 ; F. B., of Wis., $30 ; C. II. R., of Me., $20; P. P. T.,of Vt.,$25; L. W.,ofMich., $30; F. G., of L. 1., $30; H. C. W., of Mass., $25; W. J. B., ofL. I., $30; A.M. H.,of N. Y.,$30; J. J. S., of Mass., $30; E. S., Jr., of N. Y., $25; J. A., of Pa., $22; W. H. R, of Flu., $150; J. P. K., of L. I., $25. Specifications and drs wings belonging to parties with the folIowing initials have been forwarded to the Patent Office during the week ending Saturday, June 1858:— * f,. A. G.,of M:lss. ; A. J. C., of Tenn. G. H., of N. Y. ; P. T. B., of III. ; E. S., Jr., of N. Y. ; A. A., of Vt. ; J. D. T., of Ohio; B. Du F., of Wia. ; A._C R., of R- I.; J. A-, of Pa.; H. K., of Ind. ; J. p, K, of L. I. ; H. C. W., of Ma,s.; S. G., of N. Y. ; J. H.theoutlay, of Mass.; P. P. T., of Vt.
This article was originally published with the title "Correspondents" in Scientific American 13, 42, 335 (June 1858)