Scarcely less important than the rapid transference of materials from one place to another is the quick and accurate weighing of the same. If a pneumatic grain elevator were used in conjunction with an ordinary set of scales such as are to be found at a corn dealer's there would be great delay, and the advantage of the elevator would largely be lost. Similarly a mechanical transporter of coal or ore should automatically register the tonnage of the mineral handled, to prevent undue waste of time.

There are in existence many types of automatic weighing machines, the general principles of which vary with the nature of the commodity to be weighed. Finely divided substances, such as grain, seeds, and sugar, are usually handled by hopper weighers. The grain, etc., is passed into a bin, from the bottom of which it flows into a large pan. When the proper unit of weight—a hundredweight or a ton—has nearly been attained, the flow is automatically throttled, so that it may be more exactly controlled, and as soon as the full amount has passed, the machine closes the hopper door and tips the pan over. The latter delivers its contents and returns to its original position, while the door above is simultaneously opened for the operation to be repeated. A counting apparatus records the number of tips, so that a glance suffices to learn how much material has passed through the weigher, which may be locked up and allowed to look after itself for hours together. The "Chronos" automatic grain scale is built in many sizes for charges of from 12 to 3,300 lbs. of grain, and tips five times a minute. Avery's grain weigher takes up to 5 1 / 2 tons at a time.

For materials of a lumpy nature, such as coal and ore, a different method is generally used. The hopper process would not be absolutely accurate, since the rate of feed cannot be exactly controlled when dust and large lumps weighing half a hundredweight or more are all jumbled together. Therefore instead of a pan which tips automatically as soon as it has received a fixed weight, we find a bin which, when a quantity roughly equal to the correct amount has been let in, sinks on to a weigher and has its contents registered by an automatic counter, which continuously adds up the total of a number of weighings and displays it on a dial. So that if there be 10 lbs. in excess of a ton at the first charge, the dial records "one ton," and keeps the 10 lbs. "up its sleeve" against the next weighing, to which the excess is added. Avery's mineral scale works, however, on much the same principle as that for grain already noticed, a special device being fitted to render the feed to the weighing pan as regular as possible. His weigher is used to feed mechanical furnace stokers. The quantity of coal used can thus be checked, while an automatic apparatus prevents the stoker bunkers from being overfilled.

Continuous weighers register the amount carried by a conveyer while in motion. The recording apparatus comes into action at fixed intervals, e.g. as soon as the conveyer has moved ten feet. The weighing mechanism is practically part of the conveyer, and takes the weight of ten feet. The steelyard is adjusted to exactly counterbalance the unloaded belt or skips of its length, but rises in proportion to the load. As soon as the conveyer has travelled ten feet the weight on the machine is immediately recorded, and the steelyard returns to zero.

Intermittent weighers record the weight of trucks or tubs passing over a railway or the cables of aerial track, the weigher forming part of the track and coming into play as soon as a load is fully on it.

Some machines not only weigh material, but also stow and pack it. We find a good instance in Timewell's sacking apparatus, which weighs corn, chaff, flour, oatmeal, rice, coffee, etc., transfers it to sacks, and sews the sack up automatically. The amount of time saved by such a machine must be very great.

Note.—The author desires to express his indebtedness to Mr. George F. Zimmer's The Mechanical Handling of Material for some of the information contained in the above chapter; and to the publishers, Messrs. A. Crosby Lockwood and Son, for permission to make use of the same.