CANNING COLLEGE, LUCK NOW. 3
and the whole of the outer roofs are covered with a layer of terrace having a good slope outwards; the finished thickness of terrace averages 4} inches, and is composed of 4 parts brick ballast and coarse surkhi and 1 of fresh lime, these materials were thoroughly mixed and spread on the roof to the required thickness, then beaten till quite hard, a layer of fine mortar mixed with gur was then given, and the whole surface finished off by being well rubbed over with castor-oil.
The girders for these roofs are entirely of wrought-iron, and were made on the spot. For the Library and three largest class rooms they are 2 feet deep with webs 1-inch thick and flanges of double 4" x 4" x 3" L-irons; for other rooms they are 2 feet deep with webs 4-inch thick and flanges of double 3" X 3" ş" L-irons; for small porches they are 15 inches deep with 4-inch webs and flanges of double 2" x 2" x " L-irons; the girders are designed so that the load on them induces a strain on the flanges of less than 5 tons per square inch of effective section; where necessary to withstand the thrust of end arches as in porches, &c., bars were built into the walls and secured to the nearest girder by iron bolts. The girders, bolts and all iron-work received two coats of paint before being fixed in position.
The Library roof in original design was arched, and caused a very un- sightly projection in the line of front parapet. The alteration from a single arch, to arches between girders, while improving the appearance of the front elevation, necessitated some provision for lighting in place of the end circular lights; this is given by a sky-light 21" X 6' placed in the centre of the Library roof. To take the thrust of the roof arches at the ends of the space left for sky-light, strut girders are given between the four centre main girders with webs 1-inch thick and flanges on one side only of 4" x 4" x 3" L-iron, these are rivetted to main girders by L-irons 31" x 3" x 3". Round the top of the rectangular space thus formed and bolted to the top flanges of girders is a sill of sal wood 8" x 4" into which the uprights of sky-light are fixed; the sides and ends of sky-light have glazed sashes working on pivots. The roof, which is curved, is cover- ed with 1-inch planks tongued and grooved and painted with three coats of oil paint, and over this corrugated iron No. 18 BWG carried well out over ends and sides. The inside of sky-light and wells formed by main and strut girders are painted a dead white, and a very good light has been secured.
The roof of Examination Hall, which in original design is a segmental
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