CORRESPONDENTS who expect to receive answers to their letters must, m all cases, sign their names. We have a right to know those who seek information from us; beside, as sometimes happens, we may prefer to address correspondents by mail. SPECIAL NOTE. This column is designed for the general interest and in struction of our reader synot for gratuitous replies to questions of a purely business or personal natzire* We will publish such inquiries, however when paid for as advertisenwts at $1*00 a line, under the head of "Business and Personal." %MT*All reference to back numbers should be by volume and vage. A. J. S., of La. Your inquiries relative to caloric engines will be found answered in our description of the Roper improved hot air en gine, to be illustrated in our next issue, No. 17 current volume. W. H., of Pa., is running a quarter-turn belt, 60 feet long and 16 inches wide,from a 48-inch pulley at the bottom to a 52-inch pulley above. It does not run well and binders are necessary. A12 inch belt ofthesame length ran wellf or a time but subsequently required binders. He asks if there are any cases known where quarter-twist belts of these lengths and widths have run well without binders. We know of no such cases. Iu our practice we never attempted to run a belt oi either 16 or even 12 inches wide on a quarter turn, and if compelled to do so would have insisted on a greater distance between shafts than that in this case less than 15 feet. Where the limit is between widths of belts and distances between points for the quarter turn we are unable to determine. The millwright usually relies much upon his own judgment. H. B., Jr., of Canada. If an invention has been patented abroad, that will not prevent the original inventor from patenting it here unless the invention has not gone into public use before the date of his application in this country; but the term of his grant here, in such case ? would be limited to the expiring of the term for which letters patent were first issued to him abroad for such invention. If a patent exists in a foreign country, that fact would debar the granting of a patent here to another inventor, unless he could show th t he xnade Hie invention before fche date of the foreign patent, H.W. P., of Vt. Carbolic acid will not remedy the odor arising from concrete walks, in which coal tar is an ingredient. R. B., of Conn. The knitting machine to which you refer is we believe more generally used than any other. L. F. M.,of Mass. The "Patent Claims " are now issued weekly, in pamphlet form, by the Patent Office, at $5 per annum. S. A. H., of Conn. Gumbridge Co., to whom you refer, have been dealt with according to law. They were humbugs, no doubt. H. H., of N. J. There is no particular degree or dividing line that marks the difference between hot and cold, warm and cool. It is a mere matter of sensation. H. C, of Pa. We cannot admit any further discussion of the subject inta our columns. The subject is stale, flat, and unprofitable. D. T. Jr., of Pa. We recommend you to get the " Silver Sunbeam " as the best work for you on photography. S. F. M., of 111. Small pieces of brass can be melted in a sand crucible with a coal fire, but the crucible must be kept covered. You would be likely also to lose a large portion of the zinc. The best way to use up scrap brass is to melt it in with new brass, putting it in with the zinc after the copper is melted. C. E. H., of Iowa. The researches referred to as more recent than those of Joule, Rumford, Tyndall, etc., in the article entitled, " Waste and Economy of Fuel," are those of Auguste Langel, Victor De-lacour, Hirn, Zeuner, Bede, Emile Martin, and Scholl, and other able engineers, including the author of the article in question.