Permit perfect freedom to the sheets. Confine them nowhere, and separate lengths of guttering, and any other portions of a roof requiring to be made in long pieces, as much as possible. Eaves-gutters should be made in short lengths, bent in the direction of the way in which the sheet has been rolled and soldered, the solder being put between the sheets, and one sheet lapping over the other. Nor must they be screwed to the rafters, as this is a practice which occasions a constant failure in the joints of the iron eaves-gutters. Wherever a down-pipe comes, there should be a stopped end in the gutter; and the gutter should not be continued longer than possible in one place. Where it is laid behind a parapet, a separate piece of flashing will disconnect it wholly from the sheeting on the roof. For guttering, the gauge used should be increased in proportion to length; there should be a proper substance in all cases. Oak boarding will spoil the zinc, and the fir boarding should be dry-the boards with an aperture of about 1/2 inch between each. If they are damp, as much oxidation will take place on the under side of the zinc as on top of it. From experiment, it appears that the oxidation proceeds for about four years, gradually diminishing after the first three months, when it hardens into a protecting coat of a dark gray color, preserving the metal beneath from further deterioration. A sheet of zinc, exposed to the atmosphere for a series of years loses little or nothing of its weight or thick ness, and its surface remains hard and polished as enamel.