material for its support. Artistic rails are more expensive than plain ones; hence the selection of the design will often involve a compromise between economics and aesthetics, and will depend greatly upon the amount of money available for the work.

Rails can be built entirely in place, or they may be either partly or wholly cast in sections and set in position. The jointing will require careful attention; for, otherwise, the railing will have a bad appearance and even may go to pieces. A better character of construction can be secured with separately-moulded work; but unsightly joints would offset this advantage. Separately-moulded rails generally interfere much less than other types of rails with the progress of construction; besides, the moulding of the parts can be carried on at odd times in the intervals of other work. Both of these features are money savers.

Designs

The economics of design are rather difficult to determine, as the quantities involved are influenced quite largely by the individual tastes of the designer. The problem is also complicated by the facts that the unit costs of the various portions of a structure may be more or less different, and that the unit costs of different types of construction may be decidedly unlike. In general, it may be said that the unit costs are lower for those structures which have the simplest form-work; and a reduction will also be effected by decreasing the area of form-surface per cubic yard of concrete. For instance, in the case of a wall or slab, the form-cost per cubic yard will vary practically inversely as the thickness of the said wall or slab. Evidently, therefore, it is desirable to concentrate the concrete into a few large members, rather than to employ a great number of small ones.

It should be noted that reinforcing bars less than 3/4" in diameter command higher pound prices than do the larger bars. The extras for these small bars may be found in Engineering News-Record in the first issue of each month.

The economics of the designing of the different parts of reinforced-concrete structures will now be discussed in logical order.

Slabs

A primary economic problem in slab designing is that of two-way versus one-way reinforcing. Two-way reinforcing involves less concrete but more steel than does one-way reinforcing; hence it has but little advantage, unless the reduction of dead-load to a minimum be of prime importance.

Different arrangements of slab steel are discussed on pages 918 to 921, inclusive, of "Bridge Engineering"; and it will be noted therefrom that there is very little difference in the weights of the various types. Lighter