CORRESPONDENTS who expect to receive attention must give their proper names We always throw away all letters sent to us not accompanied with, the writer's name J S C, of Wis—Send sketch and description of your improvement, and write to us so that we shall know how to address you by letter D N, of 111—You inquire if a person would be infringing a patent, if he should make a machine so patented and use it only for his own family, such as a water filter or a sewing machine ? We answer certainly he would No one has a right to either make or use a patented machine in any manner whatsoever without acquiring a privilege so to do from the owner of the patent N C Y, of Mass—You can procure tailor's shears, trimmers and scissors of the very finest quality from Wendt amp; Seymour, No 29 Gold street, this city We have examined their samples, and can recommend them unqualifiedly E W, of Iowa—There are a number of doubl seaming machines now in successful use for tin working You can patent any improvement which you may have made in such machines If you will send us a sketch and description ot your plan we will examine il with pleasure H P T,, of Mass—We nave noticed with muct pleasure your success in the discovery of comets Whal has become of that monstrous one which was to pay his respects this way sometime last summer, and didn11 'i If you discover at any future time that he peregrinates towards the Scientific American office, please telegrapt us, so that we may standf rom under J C C, of Conn—We suppose every needed alteration in your case has been made, and that the letters patent will be issued at any time you may order Y oui inquiry is very blindly put, and it may be that we hav failed to understand you, and knowing nothing of the particulars of your case, we may have misapprehended what you are driving at A R McL, of N Y—Violin strings are prepared from twisted intestines of sheep, which is cleaned and twisted while wet, and then dried in a proper frame The best are made in Milan, and are sold under the name of Roman strings J F K, of Ohio—You state tbat you have been informed that a patent cannot be Bold on a writ ot" execution, and wish to know if this is the law ? A patent, like other property, passes to assignees in cases of bankruptcy Curtis says on pages 2256 :—u The interest in a patent may be assigned by operation of law, in case of the bankruptcy of the patentee" A H, of Mass—The hydrate of alumina is not a fluid, but a gelatinous mass, and it is prepared by M Meul by making a solution of common alum, and adding to it a solution of carbonate of soda until a gelatinous mass is formed This precipitate is then washed with pure water on the filter, and you have the desired compound Its formula is Al 2 O 3, 4 3 H O B F McC, of Ga—The common method of silverplating articles now practised is by the electrotype process, and requires much practice to perform it skillfully If you purchase "Smee'a ElectroMetallurgy," it will give you the information desired This work tepublished by Wiley amp; Halsted, Broadway, this city A recipe could not furnish you with all the desired knowledge W H Chester, 104 Center street, this city, furnishes electrotyping apparatus K R, of Kansas—Your discovery that lead loses its weight when immersed in quicksilver is old, and we have no doubt that the model you made operated, but there is this objection that your leaden wheel would be so quickly dissolved or amalgamated by the mercury that after a few turns there would be no wheel at all W H W, of Ind—You ask us to answer a question to which you have already received a reply, and that reply is quite correct, as you state the question to us P G R, of Va—We do not know of any printing press that would answer your purpose, neither can we inform you of the cost of cutting brass cog wheels We do not know where you can obtain such information We think we can use our columns to better advantage than to publish "perpetual motions11 G W S, of Ohio—We received your letter regarding the repointing of gold pens, but thought you were mistaken We have had demonstrative evidence of the successful repointing at a moderate cost of such pens Thos M Scott, of La, Grange, Ga, wishes to correspond with some one who will undertake to manufacture his patent fly trap upon reasonable terms L S P, of Texas—J W Nystrom, of Philadelphia, ia Ihe inventor of a neat calculating machine, but it is not of the capacity of Babbage's to which yon refer We are not aware of its price We are unacquainted with the French calculating machine which, you mention J de Y, of Texas—The work on engineering to which you refer, containing information on cements, must be "Mahan's Civil Engineering" It ia published by Wiley amp; Halsted, this city Wo arc not acquainted with any other E S W, of Ind—The best work on gasmaking and the various allied processes is Ronalds and Richardsou' s Technology, vol I, part 2 It can be obtained of H Bailliere, 298 Broadway, New York F W S, of N Y—A patented machine bought by you, without any reservation as to its use, by the person who has the legal power of sale, can be loaned or hired by you to accomodate any of your neighbors Were the law otherwise in its spirit, the farmer or manufacturer who purchased patented implements, would be obliged to work them all himself—a preposterous idea, fe*J B, of Md—You ask: ''How many revolutions per minute must a burr stone of 4)4 feet perform, to require the same power only of a 4 feet stone, running 150 revolutions per minute, each grinding the Bame quantity of wheat in the same time ?" We cannot answer this question according as it is put, because it is not a fair one It will require the same power to give the 4)4 feet stones 130 revolutions per minute as the 4 feet stone?, making 150 revolutions ; but the larger stones will not grind the same quantity of wheat as the small ones, because, although they have as great a circumferential velocity, yet they have not an equal central velocity To grind the same quantity of wheat in the same time, the 4H feet stones should require to revolve about as often aa the 4 feet stones, at least it appears so to us K M Q, of Mass—The substitution of malleableiron for wrought iron, in axes and chiaels, would allow of their being manufactured at less coet for material, but their quality would be very inferior A F O, of N Y__The best cement known to us to resist the action of alcohol, is composed of melted glue, into which some ground chalk is stirred B F B, of Pa—You can color tobacco any shade darker than its natural color, with logwood; you mnst proportion the strength of the logwood liquor to the depth of shade required The common machines for cutting tobacco are not working under a patent, they are public property R S P, of Pa—Optical glasses are first ground with fine emery to the exact form on proper tools, und afterwards polished with fine rouge powder W B G, of Ohio—Printing ink jQftn be taken out of paper by caustic soda ; but thie alkali renders the paper yellow in color Money received at the Scientific American Office on account of Patent Office business, for the week ending Saturday, March 27,1858 :— A T R of N Y, $25; L P, of Me, $20; H M, of N Y, $25; F D L, of S C, $105 ; E V S, of Miss, $55 ; C amp; W, of Pa, $30 ; H D, of Pa, $25 ; L R, of HL, $25; C B B, of 111, $10; J B, of Ind, $30 ; A B J F, of Ind, $30; R G S, of 111, $30; K C, of MaS3,$25O; S W W, of N Y, $30; GVG,ofO, $20 ; G I C, of El, $15 ; B F S, of Pa, $30 ; E B W, ofN O, $50; G Y,of N Y, $10; K F, of Wis, $30 ; J C S, ef Mass, $30; R H F, of N H, $80 ; O T W, of Pa, $30 ; S R H, of N Y, $150 ; W R L, of Conn, $85; Z N M, of Texas, $30; T J R, of Ohio, $30 ; J W G, of Vt, $5 ; M G F, of N Y, $55; J L R, of Iowa, $30 ; T K W, of*Conn, $25; J T, of Mass, $30; C L C, of 111,, $30; R amp;S, of Ohio, $30 ; J W H, of R I, $57 ; N F E, of Vt, $20 ; W DeG, of N Y, $25 ; L amp; G, of Conn, $30 ; P R, of 111, $25 ; W W, of N Y, $30 ; B J, of L I, $25 , J McN, of L I, $35; J W C, of N, Y, $25; J H W, of N Y, $12 ; J R, of N Y, $25 Speci cations and dra wings belonging to parties with the following initials have been f orwarded to the Patent Office during the week ending Saturday, March 27,1858 : I C, of Vt ; J W G, of Vt ; R J, f L I ; W R L, of Conn ; R H F, of N II, (2 cases) ; J McN, of L I ; J H W, ofN Y G V G of Ohio; J W C of N Y ; J B "of N Y; D amp; M, of Pa ; L R, of 111 ; H M, ofN Y ; A T R, ofN Y ; W Il L, of Pa; T K W, of Conn : W DeG, of N Y ; N F E, of Vt ; P B, of 111 ; W W, of N Y