J. P. D. will find directions for colored whitewash on pp. 235, 236, vol. 36.--A. M. will find directions for electroplating on p. 59, vol. 36.--H. P. can recover silver from photographers' waste by the process detailed on p. 250, vol. 27.--A. W. A.'s difficulty as to 64 and 65 squares in the puzzle can be solved by an inspection of the diagrams on p. 323, No. 21, SCIENTIFIC AMERICAN SUPPLEMENT.--I. A. will find a description of a magneto-electric machine on p. 195, vol. 34. A clock thus would go for 12 hours, and wind itself at the same time for 12 hours more, if such a machine could exist, would be a perpetual motion. As to tempering small drills, see p. 186, vol. 26.--R. B. can prevent rust on iron or steel by the means described on p. 26, vol. 25. For a recipe for a depilatory, see p. 186, vol. 34.--A. T. R. is informed that the hydrocarbon engine is reversible.--T. W. will find directions for making sand belts on p. 235, vol. 36.--M. G. should address a manufacturer of oxygen cylinders.--J. S. C., who inquires as to a water fountain, sizes of pipes, etc., should send us a sketch with dimensions.--O. L. is informed that the proper way to ascertain the relative strengths of corrugated and plain sheet metal is by experiment.--G. H. B. will find directions for making colored printing inks on p. 90, vol. 36.--P. M. will find on p. 250, vol. 36, directions for making a polishing starch.--C. H. B. can braze the ends of his brass plate to make a cylinder of it. See p. 219, vol. 36.--W. H. C. is informed that his method of fluting reamers is not new.--C. C. G. will find his method of raising coal or other weights impracticable.--E. S. G. had better test so simple an experiment and satisfy himself.--W. H. C. is informed that the most satisfactory plan would be to get his tools nickel-plated. (1) J. H. N., of Christ Church, New Zealand, asks: Is the stearin from which the olein has been extracted by Dr. Mott's process fit to be made at once into good stearin candles, without any further treatment? A. Yes. (2) B. B. says: I wish to express the strongest coloring matter from certain herbs, sage leaves, for instance. How can it best be done cheaply and quickly? Evaporation during several days, after boiling and simmering, has the effect; but it is inconveniently slow. The color produced is a medium brown. A. Dry the leaves, etc., thoroughly, and grind to a fine powder. Digest this for several days in enough warm water to thoroughly moisten it throughout. Then add enough wood naphtha to make a stiff paste, and after standing an hour transfer to a fine linen bag and express the thick liquid in a screw press. 2. Is there anything that will set the color? A. Try a strong hot solution of alum.