CORRESPONDENTS who expect to receive anawers to their letters must, tti all cases, sign their names. We have a right to know those who seek in formation from us; beside, as sometimes happens, we may prefer to ad dress corre-wondents by mail. SPECIAL NO TE.— This column is designed for the general interest and in struction of our reader,%not for gratuitous replies to qtiestions ofatmrely business or personal nature. We will publish such inquiries, howener-when paid for as advertisemets at $1*00 a line, under the head of ''Business and Personal." IW All reference to back numbers should he by volume and page. J. D. S., of Conn.—It is impossible for us to assign a cause for the spoiling of the water in the tube of your pump under the circumstances as described by you, although it would doubtless become apparent upon inspection. There is no reason why the outside of a tube should affect the water differently than the inside, if all other circumstances are similar. S. W. A., of Pittsburgh.—Nothing short of an. extended and abstruse article would give a satisfactory answer to your queries about modelling hulls of vessels. The peculiarities of the model you mention cannot be isolated from other considerations, which have an important, relation to the subject. T. R. M., of Ohio.—The idea of propelling vessels by ejecting water from the stern is old. R. S., of 111.—Rubber corks for chemical apparatus although somewhat expensive are for many purposes excellent. You can obtain them of any dealer in chemical apparatus. C. D. M., of Tenn.—The " watermark " is given to paper in the process of manufacture. Itismade by a figure woven upon the wire cloth upon which the pulp is deposited. These figures leave the paper thinner where they occur. A. H., of Conn.—The cables of the proposed East River Bridge will be made on the the position they will occupy when the bridge is completed. Their construction will require extensive preparation and machinery. Such cables could not be transported after they were completed. A. E. B., of Miss.—The washing of binoxide of lead, prepared by Fresenius' method,is a tedious process,and will require patient manipulation. E. P. W., of Wis.—Dampness in cellars is frequently caused by want of proper ventilation. From your description we judge this to be the difficulty with your cellar. G. R. M., of Mich.—A pair of pincers with platinum points will enable you to hold the substances named in a very hot fiame, without damage to the pincers. T. E. D., of Pa.—You can reduce the friction on your two wood surfaces without oil by blaCJjleading them; It will not need frequent reileal.