The dimensions of the engine vary according to the capacity, which is usually expressed in terms of the amount of dry pulp the beater will hold, and the following figures may be taken as giving the average sizes:-- -----------------+----------------+---------------- -- | 2 cwt. Engine. | 5 cwt. Engine. -----------------+----------------|---------------- Length | 11 ft. 0 in. | 16 ft. 0 in. Width | 5 ft. 6 in. | 8 ft. 0 in. Depth (average) | 2 ft. 3 in. | 2 ft. 9 in. Diameter of roll | 3 ft. 6 in. | 3 ft. 6 in. -----------------+----------------+---------------- Sundry modifications in the form and arrangement of the beater have been tried from time to time. In 1869 Granville patented the substitution of a second beater roll in place of the stationary bedplate for the purpose of hastening the operation. Repeated attempts have been made to construct a beating engine with two or more rolls, but it is evident that such a device could hardly succeed, since it would be impossible to ensure proper adjustment of the rolls, and in that case one roll might be doing all the work. The first machine of this type was patented in 1872 by Salt. Similar beaters were devised by Forbes in 1880, Macfarlane in 1886, Pickles in 1894, who proposed to use three rolls, and Partington in 1901. Hoffman describes a beating engine which was working in America containing four rolls, as shown in the diagram. _The Umpherston._--A notable modification of the Hollander, having an arrangement by which the two channels of the engines are placed under one another, and one which is largely used for fibres, is the Umpherston. Several engines differing in detail, but embodying the same principle, have been built in imitation of this one. [Illustration: FIG. 50.--Umpherston Beater.] Bedplates of large working surface were first tried in England by Cooke and Hibbert, in 1878, but in practice it has been found that no serious deviations from the narrow type of plate are of much value. As a matter of fact it is held by some paper-makers that one or two knives would be sufficient if they could be relied on to keep true and in proper adjustment. _The Circulating Type of Beater._--The addition of some device for keeping the pulp in circulation apart from the action of the roll has received considerable attention. The early experiments in this direction with the Hollander led ultimately to the construction of the engine of the circulator type mentioned in class 2. [Illustration: FIG. 51.--Section of Umpherston Beating Engine.] Thus, in 1872, Nugent patented a special paddle to be used in the Hollander, by which the pulp in the trough of the beater was impelled towards the roll. Many other plans were tried for this purpose, and details can be seen in the List of Patents (see page 192).