In Fig. 24 is illustrated a =single-acting, checking-spring hinge=. This spring hinge is known as the _Bardsley_, and its mechanism, which is enclosed in a cast-iron box, is shown at (_a_). This box, or case, is set into the floor, the top plate being made flush with the top of the floor, as shown at (_b_). The operating bar, or pivot, of the hinge has a square end, as shown at _a_, that engages with the plate secured to the bottom edge of the door, and is connected to the mechanism by means of a crank and connecting link, as at _b_. After being set into the floor, the cast-iron box, or case, containing the spring, piston cylinder, etc. is filled with oil or other non-freezing liquid, and sealed by means of the top plate _c_. The action of the door in opening compresses the spring and operates the piston in the cylinder. The spring operating to close the door also moves the piston and forces the oil in the cylinder out through a by-pass, the flow being regulated by the adjusting screws _d_, which are on a level with the top plate. In this manner, the door is closed surely but gently, from which the hinge derives its name of checking-spring hinge. Hinges of this type can be used without any modification of the door or frame, but are not extensively used on account of their high price and the cost of application. [Illustration: FIG. 24] For pivoting the door at the top, there is provided a top pivot and plate, as illustrated at (_c_). This pivot is applied to the edge of the door stile. Both the top pivot and bottom hinge plates on the door are offset. [Illustration: FIG. 25] Double-acting floor hinges are rapidly displacing double-acting spring hinges. This is due to the fact that when the former hinges are employed the door is pivoted at the top and bottom and the weight of the door is not carried by the coils of the spring, as in the double-acting spring hinge. The floor type of double-acting hinge carries the weight of the door on a ball bearing in the box, or case, let into the floor, as shown at _a_, Fig. 25, the coil performing only the function of closing the door. The hinge illustrated is not only a double-acting hinge, but is also a checking hinge, and for this reason is known as a =double-acting, checking-spring hinge=. In operating, this spring hinge not only closes the door, but prevents it, when closing, from oscillating after the door has reached its neutral, or closed, position. There are numerous double-acting floor hinges in the market that are not of the checking type. Some of these are the _Atlas_ and _Simplex_, made by Bardsley, the _Bommer_, made by Bommer Brothers, together with the _Chicago_, _New Idea_, _Matchless_, _Chief_, and _Columbia_, made by various manufacturers. All of these hinges embody practically the same principle, but differ somewhat in mechanism.