G. P., of N. B.Hollow grate bars are now being employed in several locomotives, and no difficulty is experienced, we have been told, in maintaining the circulation in them. You will find the illustration of hollow grate bars for furnaces on page 204, Vol. III. (old series), of the SCIENTIFIC AMERICAN. P. B. C, of Va." Morfitt on the Art of Tanning" was published by H. C. Baird, of Philadelphia, in 1852. It does not contain the latest American patents. J. B., of 111.Parchment requires to have all the grease extracted from it, for the purpose of writing. It is there, fore steeped in milk of lime during its preparation, to effect this object. The bright red color on morocco is dyed with cochineal, a little muriate of tin and cream of tartar. Carmine dissolved in aqua ammonia makes a beautiful red on leather, when applied with a sponge. Bed Russia morocco is imported. O. C. S., of N. Y.If B knows that A was a previous purchaser, then B has no claim upon A'a territory. In view of such knowledge, the fact of the non-recording of A's assignments gives B no right to A's territory. The papers have been forwarded to W. D. H. B. M., of N. Y.Tho pressure on the bottom of a vertical pipe one inch in diameter and 23 feet long, filled with water, will be 8.5 lbs. A 2-inch column of water will exert precisely four times the pressure of a 1-inch column, both being of the same hight. The pressure of the atmosphere on the surface of a 1-inch circle is 11.78 Iba, which, added to the pressure of the wator in the 1-inch pipe, makes 20.28 Iba. A brick wall will be preserved from the effects of the heat of a fire, when the fame is kept well wet all the time during the fire. J. H. N., of Tenu.You are correct in stating that the cause of difficulty in telegraphing during wet weather is owing to the absorption of electricity by the moisture ; but insulated wires (those coated with gutta-percha) are not patentable as a preventive of the evil, because such conductors have been frequently used already. You are mistaken in supposing water to be the best conductor of electricity. Pure rain water is a very poor conductor ; it is to copper wire as 1 to 40,653,000, according to Mr. Farmer, o^ Botton, who has made many experiments on the resistance Of Bubstanccs to the electric fluid. S. & Co., of Conn.You can obtain nil kinds of steel from Sanderson, No. 16 Cliff-street, this citya Sheffield house. F. A. W., of Ky.There will be no difference in the quality of corn for feeding hogs, whether it be first ground and then boiled, er whether it is first boiled and then crushed between rollers. The employment of a tank with a false bottom, placed above a steaming kettle, for cooking food for animals, is an old and useful arrangement, and should be more generally used by farmers. You cannot obtain a patent for your arrangement of boilers and crushing rollers, as the system is old. G. H., of N. Y.The best varnish known to us for coating bright iron, to prevent it from rusting, is clear copal ; it contains oil and is not liable to crack. The metal cadmium is rare but may be obtained in this city. Sheet copper cannot be welded into a maes, like iron. We are much obliged to you for your kind, ness in sending us a club of subscribers. D. N. T., of Ga.Instead of "awaiting the turn of events," as you term it, we think your apprehension should stimulate you to make an application for a patent immediately, while you are required to pay only $30 for government fee. You ueed not fear but that the rights of a patentee will be ever respected, let the inventor reside where be will. The rights of French and English citizens and all other foreigners who have taken patents In this country are just ns much protected under our In.we aa the rights of the patentee who resides in Washington city. To be eure, the right to this protection has coBt the Englishman and Frenchman more than it has the resident of Washington city (the government fee being, in the first case, $500, in the next, $300, and in the last, only $30), but the law that protects the one in the peaceable enjoyment of his propertypatentprotects all, and after the patent is granted, all are on au equal footing. H. C, of N. 0.Our new volume will commence intwo weeks. We are glad tokaow that you are forming a club in your town. In a few days we ehall issue an edition of the Patent laws and information upon all subjects connected therewith. Inventors, patentees and assignes will und it an indispensable work for their use. S. H., of Gii.You can procure such brass castings as you want, of George Pollock, of this city. We can recommend S. C. Hills, No. 12 Platt street, this city, aa a reliable dealer in machinery. A. T., of N. Y.The plan of steaming wood to season it has been long practiced in this country. By calling at this office, you will be able to learn all you want to know about our patent laws anil about the patentability of your inventions. H., of Pa.You ask:"Would a shaft support a greater weight, hung on the middle, when rapidly than when slowly revolving ? " Answer.""It would not." N. T., of N. J.There is no single work known to us whick contains illustrations of all kinds of machinery. Ure's Dictionary of Arts and Manufactura will, perhaps, come nearest the kind of book which you want. J. L., of Pa.Your article on Pittsburgh and its steel manufactures has been received and will meet with attention. P. J. K., of Wis.It is well known, according to the discovery of Sir Humphrey Davy, that a piece of zinc soldered to a piece of iron prevents the latter from rusting. The zinc corrodes, and in doing so establishes an electric action which protects the iron, as you have described. You could not obtain a patent for such a discovery. tulj C. C, of Ohio.We do not think there is any chance for a patent on your grain separator. The same device is covered by Sander* patent. We advise you to make a model of your grain dryer and send it to us, as we think it contains patentable features. Snead's patent does not embrace the same elements. D. F., of N. Y.We arc afraid that india-rubber balls would not answer for the valves of pumps in tanneries. The tanning liquors would be liable to affect the india-rubber by coating it? Eui'face. Some of the rubber companies, however, might agree to make suitable valves for you. W. O. H., of Pa.We do not know of any better mode of pulverizing rosin than to pound it in a mortar and icreenlt through a eieve. The blows should be light, so as not to make the rosin stick to the crusher. In grinding it between stones, the etonesshould be light and have a. rapid rotation.