. Cassier's magazine . ey penetrate therock to a depth of 4 inches. A rail-way track is temporarily arranged torun along the middle of the its means concrete is readily sup-plied at the points desired, and thefloor constructed. The invert is notconstructed continuously, but a setof alternate sections is first laid form consists of two steel platesof 3/16-inch steel. An angle-iron isfixed at top and bottom on two are placed one on each key,and thus constitute the staples on each side keep themfrom spreading. The invert is to be16 inches thick. Concret
. Cassier's magazine . ey penetrate therock to a depth of 4 inches. A rail-way track is temporarily arranged torun along the middle of the its means concrete is readily sup-plied at the points desired, and thefloor constructed. The invert is notconstructed continuously, but a setof alternate sections is first laid form consists of two steel platesof 3/16-inch steel. An angle-iron isfixed at top and bottom on two are placed one on each key,and thus constitute the staples on each side keep themfrom spreading. The invert is to be16 inches thick. Concrete is dumpedin place. Three-inch steel shaftingis rolled over the top of the steelforms and a smooth surface will thus be seen that the forma-tion of the invert is a very simpleprocess. The ground and key blocksform the under surface of the steel forms are the end pieces,and the upper surface is brought toshape by the steel the alternate sections are to be 437 43» CASSIERS MAGAZINE. COLLAPSIBLE STEEL CENTERING FOR CONCRETE ARCH WORK. BLAW COLLAPSIBLE STEEL CENTERING COMPANY, PITTSBURG poured the steel end pieces are dis-pensed with, as the ends of the sec-tions already cast are sufficient. Theroller is 16 feet in length, and so hasa 6-inch allowance at each end. Theinside faces of the steel forms aresmooth, the angle-irons being placedon the outside. The lower one as-sists in holding the form erect; theupper one affords a suitable surfaceof contact for the roller. The sta-ples afford an easy method of set-ting and dismounting. The con-struction track is carried on smalltrestles, and is sufficiently elevatedto permit the concreting of the in-vert. The sides and crown constitute,however, a more difficult piece ofwork. It is here that the Blaw cen-tres find their service. The sectionsfor the inside shell are each 15 feetin length. Each section consists ofthree sub-sections, each 5 feet sub-section is jointed parallel withthe axis of the
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