Of late years the elastic force of steam has been introduced to give the necessary pressure, and the patented improvements by Mr. John Hall, jun. (of Dartford), which we have now to describe, consist in the peculiar method by which this power is applied, a a (Fig. 1) are two elliptical iron cams, firmly fixed on the horizontal shafts of two cog wheels, which gear into one another; B B b b, are massive iron plates, between which the seed bags c c, in their envelopes, are placed; d is the steam cylinder; e the piston to the same, which, when raised by the force of the steam from underneath, elevates the beamf, and the connecting rods g g; these being attached to the levers h h, turn the cams so as to press against the plates B B; which pressure is continued until the cams arrive with their longest diameters in an horizontal direction, as shewn by Fig. 2. By these means the oil is squeezed out, and received into a proper receptacle underneath. On the other side of the steam cylinder, another aparatus, similar in all respects to that shewn, is fixed, and moved by the same power; but in these the longest diameters of the cams are placed in a reverse direction, or at right angles with those in the engraving; so that when the utmost pressure is excited on one side of the cylinder by the ascent or descent of the piston, no pressure whatever is given on the other, and the bags may be removed to be emptied, and replenished with a fresh quantity of seed.
The employment of elliptical cams is altered with a very great convenience, which we ought not to omit noticing. The two innermost plates B B are connected together by means of straps, as shewn at i i (Fig. 2) stretched out while the cams are exerting their pressure; when that pressure is relieved by the cams being turned into the position of these in Fig. 1, the connecting straps ii are raised, and the two plates B B are drawn towards one another; the bags are then perfectly free to be removed by the workman, to be filled again and replaced; and so on alternately, on opposite sides, at every ascent or descent of the piston. The steam pressure upon the piston, employed by the patentee, is from forty to fifty pounds upon the inch, nearly the whole of which, owing to the simplicity of the apparatus, is transferred to the end of the cams, where the power is increased according to the ratio of their surfaces, compared to that of the piston. A steam apparatus is constructed near to each pair of cams, for the convenience of heating the seeds, with means for discharging the cake and refilling the bags.
In the year 1828, the Society of Arts presented Mr. Cogan with their silver medal, for the communication of a process for purifying rape and linseed oils. Mr. Cogan's process, though resembling M. Thenard's in the first part of it, is completed by the judicious introduction of steam; by means of which the oil appears to be almost entirely freed from acid, and the black feculent dregs subside in the course of twelve hours, leaving the upper portion of the oil quite clear, and greatly improved in colour, and in those qualities for which it is valued by the painter. The quantity of oil that he operates upon at once is about 100 gallons. For this, three quarts, that is about ten pounds, of sulphuric acid, oil of vitriol, is required. The acid is to be diluted with an equal bulk of water. The oil being put into a copper pan, of the shape of a boiler, two quarts of the dilute acid are to be added; the whole is then to be stirred up very carefully for an hour or more, with a wooden scoop, till the acid is become completely incorporated with the oil, and the colour of this last has become much deeper than at first. A second similar quantity of acid is to be added, and mixed with the oil, the same as the first was; and after this the remaining third part of acid is to be added.
The stirring of the oil is to continue incessantly about six hours in the whole, at the end of which time the colour of the mixture will be almost that of tar. It is then to be allowed to stand quiet for a night, and in the morning is to be transferred to the boiler; this is of copper, and has a steam pipe entering it at the bottom, and then dividing into three or four branches, each of which terminates in a perforated plate. The steam thus thrown in, passes in a very divided state into the oil, penetrates into every part of it, and heats it to the temperature of boiling water. The steaming process is to be continued for about six or seven hours, at the end of which time it is to be transferred to a cooler, of the form of an inverted cone, terminating in a short pipe, commanded by a stop-cock, and also having a stop-cock inserted in its side, a few inches from the bottom. After remaining a night in the cooler, the oil is fit to be withdrawn: for this purpose, the cock at bottom is opened, and the black watery acid liquor flows out. As soon as the oil begins to come, the cock is closed, and that in the side of the cooler is opened. From this the oil runs quite clear and limpid; the whole of that which is still turbid remaining below the upper cock.
The purified oil being drawn off, that which is turbid is let out into a reservoir, where it either remains to clarify by subsidence, or is mixed with the next portion of raw oil.
The following is the patented process adopted by Mr. M. Wilks, seed crusher of Dartford, for purifying the oil from linseed, as well as other seeds, by expression. Into 236 gallons of the oil, six pounds of oil of vitriol is to be poured, and be well mixed by agitation or stirring about for three hours. Six pounds of fuller's earth is next to be mixed up and thoroughly incorporated with fourteen pounds of hot lime, and thrown into the vessel containing the oil and vitriol, when the whole is to be kept in agitation for about three hours more. The foregoing mixture is next to be turned into a boiler containing a quantity of water equal to that of the oil, and the whole is then to be boiled for another three hours, during which time the liquid is to be continually agitated by stirring. The fire may now be extinguished, and when the materials have become cool, the water may be drawn off, and the oil will be found clarified, which will become brighter and more fit for use after standing some time.