Scientific American Supplement, No. 561 | Page 3

situated above the box in which raw cotton is thrown. On the top of the ram head there is a loose lashing plate, which, at the finish of the action of the rams, is locked in the cell by bolts actuated by a suitable locking gear. While in this cell the bale has the lashing ropes put round it, and then it is placed under the large rams for the final squeeze, during which the ties or ropes are permanently secured. Thus neither of the small presses has even to wait while its box is being filled, or while the previously pressed bale is being lashed. Even in the large press, when the ties are finally fastened, the time occupied does not exceed three-quarters of a minute, and is often much less.
[Illustration: COMPOUND HYDRAULIC PRESS. FIGS. 3 and 4.]
This press is shown in Figs. 3 and 4. The small rams are arranged at either side of the large ones, which, in this case, are not inverted. To each of the smaller presses there is a pair of boxes mounted on a vertical column, around which they can revolve to bring either box over the rain head. When the left hand rams rise, the material is delivered into the cell, D, which previously has had its doors (Fig. 4) closed. To permit of the cell, D, being moved out of the way, it is mounted so that it can revolve on one of the columns of the main press, first into the position shown at B (Fig. 4), and afterward to C (Fig. 3). While at D, the bale in the cell (called from its construction a revolver) is partly lashed, the ties or ropes being put into position. It is then rotated until it comes over the large rams, where the bale is still more compressed and secured.
It must be admitted that this press provides for the greatest possible economy of time, and for the largest output, for the capital employed, which can be attained. The rams and the men are constantly in action, and not a single moment is lost. For filling each box 78 seconds are allowed, and there is ample time for the preliminary lashing.
[Illustration: COMPOUND HYDRAULIC PRESS. FIGS. 5 and 6.]
Figs. 5 and 6 show a modification of this press, designed to turn out sixty bales per hour. It has only one set of long-stroke rams, with three revolvers. The bale receives its preliminary lashing while in the position, B (Fig. 6). Fifty-three seconds are available for filling the box, and the same time for the preliminary lashing. It is found, however, that three-quarters of a minute is sufficient for the complete hooping of a bale.
[Illustration: COMPOUND HYDRAULIC PRESS. FIGS. 7 and 8.]
Figs. 7 and 8 show a similar press intended for jute pressing. This has only one box, which is fixed, as the material has to be packed in an orderly manner. Its speed is sixty bales an hour.--_Engineering._
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JET PROPELLERS.--HYDRAULIC PROPULSION OF VESSELS.
Certain mechanical devices appear to exercise a remarkable influence on some minds, and engineers are blamed for not adopting them, in no very measured terms in some cases. It is not in any way necessary that these devices should have been invented by the men who advocate their adoption, in order to secure that advocacy. The intrinsic attractions of the scheme suffice to evoke eulogy; and engineers sometimes find it very difficult to make those who believe in such devices understand that there are valid reasons standing in the way of their adoption. One such device is hydraulic propulsion. A correspondent in a recent impression suggested its immediate and extended use in yachts at all events, and we willingly published his letter, because the system does no doubt lend itself very freely to adoption for a particular class of yachts, namely, those provided with auxiliary power only. But because this is the case it must not be assumed that the jet propeller is better than screw or paddle-wheel propulsion; and it is just as well, before, correspondence extends further, that we should explain why and in what way it is not satisfactory. The arguments to be urged in favor of hydraulic propulsion are many and cogent; but it will not fail to strike our readers, we think, that all these arguments refer, not to the efficiency of the system, but to its convenience. A ship with a hydraulic propeller can sail without let or hindrance; a powerful pump is provided, which will deal with an enormous leak, and so on. If all the good things which hydraulic propulsion promises could be had combined with a fair efficiency, then the days of the screw propeller and the paddle wheel would be numbered; but the efficiency of the hydraulic propeller is