HINTS TO CORRESPONDENTS. Name and Address must accompany all letters, or no attention will be paid thereto. This is for our information alld not for publication. llel'rrciH'OK to former articles or answers should give date of paper and page or numer of questIO.n. InqnirioM not paperanswered m reasonable time should be repeated ; correspondents will bear in mind that some answers require not a little re.earch, and, though we endeavor to reply t all either by letter or in thie department, each must take his turn. ii y r r* wishing to purchase any article not advertised in our columns Will be furnished WIth addresses of houses manufacturing or carrying the same. Special Wriiit'ii Iiil'orniiilioii on matters of personal rather ,';than general interest cannot be expected without remuneration. Srienlilic i nil Siipplcmenle referred to may be had at the office. Price 10 cents each. Itook referred to prompe0cy suppcer.edcen on receipt of price. 'liiii'i-nl eentfor examination should be distinctly I marked or labeled. (6632) l ug en - for a formula for giving a PI'atmum finish on copper. A. The appearance of platinum may be given to copper by immersion in a bath composed of \% pint hydrochloric acid, 7H ounces arsenic acid, and V/\ ounces acetate of copper. The article must be cleaned before immersion, and left in the bath till it has the color of platinum. (6683) A. W. F. asks how to make lye on a small scale. A. Hickory ashes are the hest for making common washing soft soap (when it is not de.irable to use the potash lye), but those from sound beceh, maple. or almost any kind of hard wood except oak. willanswer well. A common barrel set npon an inclined platform makes a very good leac h, but one made of boards set in a trough in V .hape is to be preferred, for the strength of the ashes is bettEr obtained, and it may be taken to pieces when not in use and laid up. First, in the bottom of the leach put a few sticks; over them spread a piece of carpet or woolen cloth, which is much better than straw; put on a few inches of ashes and from 4 to 8 qt. lime; fill with ashes, moistened, and tamp down welltamp the firmest in the center. It is difficult to obtain the full strength of ashes in a barrel without removing them after a day's leaching, and mixing them up and replacing. The top should be first thrown off and new ashes added to make up the proper quantity. U.e boiling water for second leaching. This lye should be sufficiently strong to float a potato. (6684) T. 0'B. says : Can you give me a quick process for making vinegar ? A. In this proces6' dilute alcoholic liquor, to which one thousandth part ot honeey or extract 0f malt has bee n added, is caused t0 trickle down through a mass of beechwood shavings previously steeped in vinegar and contained ir. a vessel called a vinegar generator. It may con.ist of a large oak hogshead or barrel furnished with a loose lid or cover, a rew inche. below which is fitted a perforated shelf, having a number of small holes loosely filled with packthread about six incbes long, knotted at the upper end to prevent their falling through. Several small glass tubes. long enough to project slightly above and below the shelf, are also fitted in perforatIOns ID the shelf to serve as air vents. The vessel at the lower part is pierced with eight or ten holes equally distributed around the sides at about 6 inches above the bottom to admit of the entrance of air. A small siphon tube, the upper curve of which is an inch below the air holes. serves to carry off the liqUId as fast as It accumulates at the bottom. The .lcoholic liquid, at a temperature of 75 degrees to 83 degrees Fah., is run in on the shelf and slowly trickles down through the holes by means of the packthread. diffuses itself over the shavings, slowly collects at the bot tom. and run. off by the siphon exit. The air enters by thelowerholes, passes freely throngh the shavings. and escapes by the glass tube. The temperature within the apparatus soon rises to about 100 degrees Fah., and remams stationary at this point, while the action goes on favorably. The liquid generally requires to he passed three or four time. through the cask before its acetifica tion is complete. (6685) J. B. asks : How much mnre power, if any, would be required to propel a bicycle (safety) one mile, having a front sprocket wheel of !$ inches in diameter, 18 teeth, and with a rear sprocket wheel of 2) Inches in diameter, 9 teeth, than one having both the front and rear "procket wheels 5) inches in diameter, with 18 teeth each; large wheels, 88 inches in diameter, equal conditions prevailing. excepting as to time required ? A. As power is derived from both pressure and velocity, the condition named in the relative sizes of the wheels will make no difference in the actual power required to drive the bicycle. The large wheel sprocket must run faster, ancl with it the feet must make more treads with lighter pressure for a given distance, than in the ordinary form as first named. The only value of the last named combination is on eteep, rising grades.