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CORRESPONDENTS who expect to receive answers to their letters must, in all cases, sign their names. We have a right to know those who seek information from us; beside, as sometimes happens, we may prefer toad' dress correspondents by mail. SPECIAL NO TE. This column is designed for the general interest and instruction of our readers, not foraratuitous replies to questions of a purely business or personal nature, we will publish such inquiries, however* when paid for as advertisemets at $1*00 a line, under the head of "Business and Personal J* $WAll reference to back numbers should be by volume and vage. GL J., of Me., says, " a combined steel and ironrail of excellent quality is manufactured in Portland, Me." This in commenting on an article in the Scientific American published on page 213 current volume copied from the London Engineer. We do not hold ourselves responsible for statements made by other journals and copied into our columns. C. M. B., of Conn. We propose in our series of articles on " Shafting Pulleys and Belts," now in course of publication, to give some directions in relation to pulleys and belts, relative diameters, etc., which will better meet your case than any reply we can make in this column. P. J. P., of Mass. To turn a true taper on the lathe, the cutting point of the tool should be exactly at the center of the piece which is to be turned. In ordinary turning it is better to keep the point above the center. J. H. W., of Pa. The reason why your cold chisels break is to be found in your hammering them when nearly cold, to " smooth finish* them, as you say. It is certain that this extra finish produced by hammer-ing refines the steel compacts its fibers and thus changes its texture, and consequently its before ascertained quality. It will not stand so high a temper. All the hammering required is that necessary to bring the chisel into shape while hot, changing the texture of the metal as little as may be. H. O. B. of Mich. You are mistaken in supposing that a very great distance is necessary between shafts connected by a quarter turned belt. We have seen them run at"only three diameters apart; that is, two six-inch pulleys only six inches between their perimeters, the centers of the shafts only twelve inches apart. Width of belt is an obstacle in the way of extending the principles of runn ing turned or twist belts. In ouf answer to " W, H. of Pa.", on page 251, the " 15 feet " should have been 30 feet. This matter of belts will receive further attention in a subse quent article, one of a series on " Shafting, Pulleys, and Belts " now being published in these columns. H. McD. of N. Y., will see his critical note embodied in an article on the same subject to appear soon. His suggestions are worthy the subject and will receive due attention. J. I. G., of Pa. You can brown your gun barrel by coating it with oil (sweet oil) and heating it over a fire. We prefer, however, the use of acid as giving a darker and more even color. If the surface is properly cleaned before applying the acid there will be no difficulty i n getting an even shade. B. R., of Iowa says, in relation to prevention of limy incrus tations in boilers, mentioned on page 219 current volume, Scientific American, that the use of oak saplings therein mentioned is really ad vantageous, as he has used it successfully for twelve years and neve knew it to fail. Or put half a bushel of common (Irish) potatoes in the boiler and no more trouble will be experienced. As to patent powders he has never tried them, E. H., of Masseln Shafiher's Telegraph Manual, page 605 and those succeeding,you will see sections of just such cables as you describe , containing more than one insulated conduc ng wire. M. and Sons, of 111., have a boiler 14 feet long, 30 inches diameter with 18 three-inch tubes, which become clogged with " soot" from the bituminous coal. The stack, of plate iron, rises 40 feet. The night of Btack is ample, unless adjacent structures, or natural obstacles, as hills, etc., obstruct the draft. If the boiler is horizontal there is no reason why the flues or tubes cannot be cleaned with a brush or scraper. If upright, the stack might be placed near the boiler, but not directly over it, and the elbow have an opening, or cover, for introducing the brush. Bat, after all, the truly scientific and correct way to remedy the evil is to consume the soot, which is only unconsumed fuel, and is in this case worse than wasted. We refer our correspondents to No. 9, Vol. XVII, Scientific American, first page, which contains an article on boiler-setting that may be suited to their case. N. G. P. of Del. So-called liquid glue is made by dissolving shellac in wood naphtha. A quarter of a pound, apothecaries' weight, of the gum to 3 ounces of naphtha.
