CORRESPONDENTS who expect to receive answers to their letters must, m all cases, Han their names. We have a right to know those who seelc information from us ,? beside, as sometimes happens, we may prefer to address correspondents by mail, SPECIAL NOTBi-This column is designed for the general interest and instruction of our reaaers.not for gratuitovsreplies to question.* of a purely business or personal nature. We will publish such inquiries, however-when paid for as advertisernets at $H)0 a line, under the head of "Mum-ness and Personal." q&~All reference to back numbers should be by volume andpage. C. B. F., of Mo., says : " 1st, I am about to build a house and wish you to inform me if it is good to build the basement wall of concrete ? Is it practicable, durable, and cheap, and how made? and. I think of building my cistern aboveground, a wood tank four feet from the ground, and run the water to any part of the house through pipes,f or drinking purposes, the pipe to be large enough to hold, say two pails of water, laid four feet deep under ground to basement. Will it be as cool as the water in an under-ground cistern?" Aus.—1st. It is common in this part of the country to build foundations of concrete, composed of lime, sand, water, gravel, and round or broken stones. A trench of boards is first made of the width of the desired foundation. Fill the trench with the concrete to the depth of a foot and let it stand for a day or two, or until sufllciently hard ; then put on another foot of concrete, and so go on, adding concrete and raising your trench boards as the wall rises. 3d. If the water had to passthrougha considerable extent of pipes underground it would be measurably cooled. But in your case you will get little or no benefit in the way of cooling. A. R, of N. Y.—Wo are informed by parties who are authorities on the subject, that the life of oak ties will scarcely exceed in the average, eight years for white oak and five years for red oak.although the best white oak will sometimes last twelve years in exceptional cases. They could scarcely be bought for less than from forty-five to fifty cents each f or 7Xfeet, 6 inchus, face and 6 inches in depth. The objections you name to stone ties are sufficient to condemn them but they have been obviated by the interposition of an elastic substance between the rail and tlie stone block, and this has been accomplished at an expense that perhaps does not render the scheme impracticable, taking into account the greater durability of a permanent way made of such material. But the great, and as yet nnsurmounted obstacle to the use of stone, is the proper confi ning of rails to the stone blocks. Nothing yet devised has met this requirement. C. D. M., of N. J.—A plumb lino does not always hang in a perpendicular to the earth's surface. It has been observed to deviate from this line in the vicinity of large mountains, being attracted by their masses, anil the Director oi'thelmperial Observatory, at Moscow, in Russia, has found in the immediate neighborhood of that city a deviation of nineteen seconds, decreasing in different places to eight seconds, from the sph eroidal perpendicular. These deviations are not caused by proximity to mountains, but are attributed to subterraneous cavities in the earth under the city, either filled with air or water. Very slight deflections in the plummet have also been traced to the attractions of the sun and moon. C. H. P., of 111.—A good iiquid blueing, free from acids, is the soluble, or basic Prussian blue, otherwise the ferrocyanide of potassium and iron. This substance is perfectly soluble in pure water, and may be made by adding to a solution of pure protosulphate of iron, a solution of ferrocyanide of potassium. A white precipitate will be formed which may be separated by filtration and washed. It becomes blue by exposure to the air, and may be dissolved in pure water as required. S. C. L., of Mich.—Capillary attraction does not exist between all liquids and solids. It is one of the manifestations of the attraction of adhesion, and as this attraction does not exist between certain liquids and solids, there can, insuchcasos, be no such thing as capillary attraction. Youcan raise alcohol through a glass wick composed of tubes having a very line bore. The heat of the flame will, however, be apt to fuse and close the upper ends of the tubes. B. W., of Ohio.—Any kind of glass properly annealed can be easily drilled, but it cannot be made so tough by any process now known tluit it can be riveted. Perhaps, however, you mean to ask whether glass can he joined by metal rivets; if so,yes. E. S.—A method of casting by compression is one of the new things of the age. Potters' clay is used for the molds, and the metal is forced in at the bottom by a cylinder and piston. The fineness of this kind of casting excels every other method known. By it the finest engravings can be accurately copied. N. B., of Del.—If any one sends us a letterthat contains sixteen distinct inquiries, we promise in advance that we will not answer them. There is a reasonable limit to which our timo and patience can be taxed, "out beyond that we are as likely to get oross as other good men. S. T. M.—If you have an instrument, as you say, that will quickly and accurately divide a circle into any given number of equal parts, without the trouble of spacing with dividers, and is at the same time cheap and portable, it is something that is wanted and will sell readily. D. E. F., of Ala.—There is no solvent that will reduce carbon to a liquid state without combining with it chemically. The bisulphide of carbon is a chemical compound, not a solution. T. D., of Ohio.—You are right in your opinion. The quacks you allude to will never help your eyes. The only thing you can do is to use the best spectacles you can procure. E. J., of Ky.—You will not succeed well in your attempt to grind brass cocks tight with emery. A ranch better material is molders' Bflixfl or pounded glass, R. C. Y., of Miss.—Salt exists in the form of minute dust in the atmosphere, near bodies of salt water, being carried up in the form of salt spray by the winds. D. P., of Vt.—A ball rolling down an inclined plane does not press against the surface of the plane with a force equal to its weight. A reference to some good text book on physics will set you right on this point.
This article was originally published with the title "Answers to Correspondents" in Scientific American 21, 9, 140 (August 1869)