The disinfection of a room is not complete unless the walls have been thoroughly cleansed. If they are papered, the paper must be removed and the surface beneath carefully scraped and washed. If the walls are painted, they should be washed with caustic soda. The ceiling should also be subjected to a similar treatment. * * * * * SCIENTIFIC AMERICAN. ESTABLISHED 1845. MUNN & CO., Editors and Proprietors. PUBLISHED WEEKLY AT NO. 37 PARK ROW, NEW YORK. O. D. MUNN. A. E. BEACH. * * * * * TERMS FOR THE SCIENTIFIC AMERICAN. One copy, one year, postage included $3.20 One copy, six months, postage included 1.60 CLUBS.--One extra copy of the SCIENTIFIC AMERICAN will be supplied gratis for every club of five subscribers at $3.20 each; additional copies at same proportionate rate. Postage prepaid. THE SCIENTIFIC AMERICAN SUPPLEMENT is a distinct paper from the SCIENTIFIC AMERICAN. THE SUPPLEMENT is issued weekly; every number contains 16 octavo pages, with handsome cover, uniform in size with SCIENTIFIC AMERICAN. Terms of subscription for SUPPLEMENT, $5.00 a year, postage paid, to subscribers. Single copies 10 cents. Sold by all news dealers throughout the country. COMBINED RATES.--The SCIENTIFIC AMERICAN and SUPPLEMENT will be sent for one year, postage free, on receipt of _seven dollars_. Both papers to one address or different addresses, as desired. The safest way to remit is by draft, postal order, or registered letter. Address MUNN & CO., 37 Park Bow, N. Y. --> Subscriptions received and single copies of either paper sold by all the news agents. PUBLISHERS' NOTICE TO MAIL SUBSCRIBERS. Mail subscribers will observe on the printed address of each paper the time for which they have prepaid. Before the time indicated expires, to insure a continuity of numbers, subscribers should remit for another year. For the convenience of the mail clerks, they will please also state when their subscriptions expire. New subscriptions will be entered from the time the order is received; but the back numbers of either the SCIENTIFIC AMERICAN or the SCIENTIFIC AMERICAN SUPPLEMENT will be sent from January when desired. In this case, the subscription will date from the commencement of the volume, and the latter will be complete for preservation or binding. * * * * * VOL. XXXVII., NO. 2. [NEW SERIES.] _Thirty-second Year._ NEW YORK, SATURDAY, JULY 14, 1877. * * * * * TABLE OF CONTENTS OF THE SCIENTIFIC AMERICAN SUPPLEMENT, NO. 80, FOR THE WEEK ENDING JULY 14, 1877. I. ENGINEERING AND MECHANICS.--Wrought Iron Bridge Designs: by WILLIAM O. DOUGLAS. A method of construction whereby the safety of the structure is not dependent on any single member. 2 engravings.--Steel Wire Hawsers.