longer schedule, than it is to try with each single mixer to produce the greatest possible yardage in the least practicable time.

Greater care and increased expense in mixing and placing are in the line of true economy; for they produce a stronger concrete and, therefore, justify the use of higher unit stresses and a consequent reduction in the concrete sections. This question is of especial importance for concrete slabs on long-span steel-bridges, and in long-span concrete-bridges.

Amount of Mixing Water

It has been the general practice to use very wet mixes, especially for reinforced-concrete. From the construction standpoint this is economical, as it reduces considerably the cost of handling and placing. Recent investigation, however, has shown that an excess of water reduces the strength of the concrete very materially, and makes the concrete porous; it also tends to cause segregation of the materials. The use of an excess of water is, therefore, false economy. The new American Railway Engineering Association Specification for Plain and Reinforced-Concrete contains the following requirement:

The quantity of water used in mixing shall be the least amount that will produce a plastic or workable mixture which can be worked into the forms and around the reinforcement. Under no circumstances shall the consistency of the concrete be such as to permit a separation of the coarse aggregate from the mortar in handling. An excess of water will not be permitted, as it seriously affects the strength of the concrete; and any batch containing such an excess will be rejected.

Use of Large Stones in the Mass

When the contractor is permitted, under certain restrictions, to place one-man stones in the concrete in order to save mortar, he usually thinks he has a "soft snap," but sometimes this is not the case; because, in addition to their having to be carried to the site, they must be thoroughly cleaned and wetted before being placed. This placing when properly performed takes time, and is done by man power-not by machinery. Again, such one-man stones are generally boulders taken from the river bed, where they are often found covered with moss and slime, all of which has to be carefully removed. In the old days when labor was cheap and cement expensive, these one-man stones were looked upon as plums in the pudding, but today the same volume of straight, machine-made concrete will often prove less costly than the said "plums." In case, however, there is old stone masonry to dispose of, it will generally be found cheaper to use it as one-man stone in the concrete rather than to haul it away.

Vibration and Jigging of Freshly-Made Concrete

During the past year there has been considerable talk about the benefits to be derived  by  fresh concrete through vibration and jigging;  but the