The annexed drawing is taken from a model recently brought from India and deposited in the museum of the Asiatic Society a represents a mortar about six feet high, usually formed out of a block of granite, but sometimes of wood; in both cases, there is as much of the substance sunk into the ground as remains above it; c is a pestle, the upper extremity of which fits loosely in the piece of timber d; at e is another piece of timber, attached by c c cords to d, (bypassing round the projecting pins shown) with its lower end mortised and bolted to the horizontal lever g; one of the ends of this lever is forked, as at , so as to pass into and around a groove made in the mortar; the lower part b of the mortar, enlarged in its dimensions, serves as a rest for the lever g, and to give steadiness to the apparatus. To put this machine into operation, a man sits upon the end g of the horizontal lever, which by the connecting bars e and d, cause the pestle e to press hard against the sides of the mortar, and a circular motion is given to the pestle by attaching a pair of oxen to the yoke h, who draw it round. An oil press on the same principle as this, is described by Dr. Buchanan, as being used by the oil makers of Bangalore for expressing various kinds of oil.
These mills receive a quantity of seed, equal to about 2 1/2- of our Winchester bushels, to which in the course of grinding, about 2 3/4 quarts of water are gradually added. The grinding continues for six hours, when the farinaceous parts of the seed and the water form a cake, and this having been removed, the oil (about 5 1/2 gallons in quantity) is found clean and pure in the bottom of the mortar, from whence it is taken by a cup. The mill requires the labour of two men and four oxen, and grinds twice a day, thus making, in the whole, but 11 gallons per day; and if this be all that so large a machine and so great a power can perform, how miserably ineffective must be the Singalese machine we first described. The writer of this article was so forcibly impressed with this defective mode of oil-pressing a few years ago, as to lead him to devise some powerful machine, in which the combinations should be few, of the simplest kind, and that should be easily made by the roughest rural workman at a trifling expense, and be, as much as possible, self-acting. The approbation which the principle of these presses have met with from professional engineers, and the practical experience which the inventor has had of their utility and convenience in a nearly similar application, induces him to give a brief description of them in this place; in the perusal of which the reader will bear in mind that they are especially designed for the rural manufacture of oil on the spot where the seeds grow.
This machine consists simply of three pieces of wood; an upright piece is fixed firmly in the ground, (a tree would answer the purpose well,) near the lower end of which, and also at the upper extremity, are projecting pieces, the upper one forming the joint of the long horizontal lever, and the lower one the joint of the short vertical one; to strengthen these joints a strap of iron is laid over them, and round the upright post, and iron bolts are passed through each to form the centre, or fulcrum, to each lever; the hand near the middle merely serves as a stay to support the vertical lever when it is thrown back. It will be observed that a roller is fixed to the upper extremity of the vertical lever, which, running upon the inclined plane of the horizontal lever, renders the friction of these parts, when in contact. very trifling: but what we consider as the most important result of this peculiar combination of two levers (which are both of the second class) is, that the effect of the power employed is but little at the commencement of the operation, but that the pressure is continually increasing during the operation, and becomes prodigiously great towards the close of it, which is owing to the pressure on the vertical lever constantly accumulating (of itself without attention) as it approaches the fulcrum of the horizontal lever.
Now this is precisely what is wanting in oil or wine-pressing: if a great pressure be given at the first, the bags burst and the liquid is lost. It is obvious, from the sketch, that the Indian who is seated in a swing, suspended to the lever, is the acting force: and as this force is obtained not only without labour, but by rest to the individual, there cannot be an easier mode of producing a mechanical effect, especially as some attendance to the process going forward is necessary. A shoemaker, or a tailor, might, indeed, carry on the business of their crafts, and, at the same time, work an oil or a wine-press upon the same principle. The design having been made with reference to the conical bags employed in India for the purpose, will account for this peculiarity in the drawing, as well as in the subjoined modification of the machine, which is merely an extension of the principle to the forming of a double press. By this arrangement double he effect is produced at about half the additional cost of one press; and if both presses were worked together (which might always be the case), instead of the central post being fixed in the ground, it might be put on a movable stand, as the weight of force of one press would counterbalance that of the other.
This figure likewise shows two convenient modes of working the press with very little attention; to one of the horizontal levers a rope is suspended, having hooks at convenient distances, upon which such weights may be hung as may be found necessary to give the required pressure; to the other is suspended a bucket (the capacity of which would be regulated by the circumstances), to take advantage of a descending current of water (if the locality admits of it), or of a reservoir, or supply pipe, that might be raised to a proper elevation for filling it; when the operation is completed, as represented on one side of the press, the bucket falling against a tail-piece fixed upright in a channel or gutter, opens a valve, lets all the water out of the bucket, and relieves the press from the force of its weight. Thus in a situation where water is plentiful, a number of large presses, charged with the necessary materials for obtaining oil, or wine juice, might be filled over-night; the next morning the buckets would be found discharged of their water, and the previously empty recipients be found filled with oil without any attendance whatever.