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H. G. F., of Ill.The most convenient substance that yon can use for deafening floors is dry sawdust. You should heat it to about 2120 Fah., in drying, so as to desti'oy the eggs of insects which may be in it. Graphite paint, made of blacklead and linseed oil, is perh.ips the very best to use for tin roofs from which rain water is conducted for domestkpurposea. Lead paints if absorbed by the water, are poisonous ; but graphite paint is quite innocuous. If a tin roof is perfectly tight, there no necessity for painting it on the inside, in your region. FAIR PLAY.Your article reviewing the position taken by us in reference to the Revisionary Board at the Patent Oftke is accepted, and will appear in our next number. S. F. M., of S. C.Either iron or cedar wood will make a pipe for a pump not injurious to health. Lead is dangerous. J. C. S., of Mo.The plan of generatmg steam oy dropping water on hot iron has received a great deal of attention. So far, it has not been practically successful. J. l\IcN., of'Iowa.Several hundred feet of the Atlin-tic telegraph cable have been raised, and the cause of its failure ia known. The coating n-as imperfect, and the salt water found its way through and rusted the conductmg wire. B. F. B., of Mass.Your letter is interestmg, but too long. As you say, it is one of the plainest problems in the philosophy of mechanism that the water by Giffard's Injecter is carried into the boiler by the momentum of the condensed steam. J. F. A., of N. Y.The construction of carpenters' rules so that they may be easily converted into a square is not now. G. B. and S. D., of N. Y.Your communications are received, but they are not exactly adapted to our paper. A. F. 0., of N. Y.White crayons are made of refined pipe clay. A piece of hard chalk is about as good for writing on blackboards as a crayon. A. G. W., of lud.There is no method known to US of furnishing a sufficient suppU'of nil' to a diviiig bell but by a force pump. S. 'V. R., of Wis.Wc have not seen any chair in use with movable rockers. The metal pbtcs of thermometers nwy be laid off ill the common *^ measuring machines" which are manufactured by J. Gould, ofNewnrk, N. J. We do not know their price. J. A. B., of Va.Wc arc nf)t aware of any patent having been issued for a device to measure distances accurately in the manner you propose ' but we iiave seen it stated in some of the English publications that "slights" of this character were used on some of the English prize rifles. N. P. C., of Conn.'Ve have in press an edition of Patent Laws, which will also contain much other information relative to the best. mode of obtaining patents, tht^ nature of caveats, re-issues, &c., aad much other information of practical use to the inventor, patentee and purchaser of patents. Also, a digest of the Patent L,iw3 of foreign countries. As soon as the work is out yon will find it advertised- in the columns of this paper. The H supplement" to our regular issne, which we published sometime since, contains all the information we think yon require concerning the stamping of iiatrnted machines with the date, and the penalty for neglecting to do so. Sen! two three cent stamps, and we will mail you a copj'. H. G. D., of S. C.You will find a full description or the " Drummond Light," with an engraving illustrating the mode of constrncting an apparatus, on page 161, Vol. II. (1847), of the SCJENTIF1C AMERICAN. In the same volume is an engraving ofthe celebrated speaking machine of Professor Faber, on which it is said he spent twenty-five years of incessant labor. The invention at^ctf'{l mucti attention at tlut time, hut we have never heard of it since. We sn.w it a niKober of times, and considered it theiiiost wonderful piece of m('ch;mif-:m we ever .saw. S. of C. E.We have received yom sknteh of the burglar al.arm, by which the gas light is m.ade to flume up wwhen a \,--mdow or door is I'aieedor opened by a burglar, \Vti have secii se.vera! similar devices. The burglars in this part of the civilized world are so crafty that they take care to become acquainted with the whole details of a house before they make an attempt to enter and rob it. F. N. B., of '^^i.s.It woild hp, very 0xx:pemi\'e to gal-vsinize the large plates of iron that nr:- used in making common steam boilers. For light boilers, such as the one you intend to employ, which will have to stand hUe freqnen 1 y, we think it will be advantageous to galvanize, the metal, in order to protect it from rapid corrosion. H. G. L., of N. Y.Regarding hydrodynamics and iiitnia. Cr'G think \-OH nrvv find t^ho mfurmatjoB ^Mre-^ in Ha-^ Jn I ) i kj-i f une. it b jlUh;i S. T., of l'a.After cast iron has been hardened from the liquid to the solid state, it is atUl at a. temperature 2492 ; and in cooling down from this temperature it shrinks. But in the process of hardening it expands, as is shown by the abseIl ce of hollows in any part of the casting. A. S. Y., of Md.The idea of your friend that he can arrange machinery to carry back his water upon his wheel after he has once Uf'!ed it, and thus gain power, is a fallacy. It belongs to that class of delusions which are grouped under the general term of "perpetual motion." H. N. B., of N. Y.The best way to clean a meerschaum pipe is to boil it for a few seconds in a dihlte solution of salsodaor the ley of wood ashes. This will convert the essential oil of the tobacco into soap, which may be washed away in '"arm water afterward.
