OILS, MANUFACTURE OF. 



OILS, MANUFACTURE OF. 



28 



coarse canvas, which are piled or laid upon one another to the number 

 of about a score, and exposed to gradual compression in a screw-press ; 

 the oil which flows from the cabas, which is the pure virgin oil, is 

 conducted by channels into casks or stone cisterns partly filled with 

 water, on the surface of which it floats so that it may.be readily col- 

 lected by skimming. When the oil ceases to flow, the mass of pulp is 

 taken out of the bags, mixed with boiling water, and treated aa before, 

 but with an increase of pressure. The second quality of oil thus 

 procured is quite fit for table use when fresh, but is apt to become 

 rancid by keeping. After skimming off the oil which accumulates on 

 the surface, the subjacent water still retains a good deal of oil, by the 

 intervention of the mucilage ; but after long repose in a large cistern 

 the oil and water separate, and the water may be drawn off from 

 below. This oil, however, is of very inferior quality, and can only be 

 used for factory pin-poses. A still coarser kind of oil is finally procured 

 by crushing the marc, or solid residue, hi a mill, so as to break the 

 stones, boiling it with water, and re-pressing it. All the oil must be 

 i >y keeping in clean tuns, in an apartment heated to at least 60 

 Fahr., for twenty days ; after which it is run off into strong casks, 

 cooled in a cellar, and then sent into the market. 



Olive oil is refined, for the use of watchmakers, in the following 

 way. Into a bottle or phial containing the oil, a slip of sheet-lead is 

 immersed, and the bottle is placed at a window, where it may receive 

 the rays of the sun. The oil by degrees gets covered with a curdy 

 mass, which after some time settles to the bottom, while itself becomes 

 limpid and colourless. As soon as the lead ceases to separate any 

 more of that white substance, the oil is decanted off into another phial 

 for use. 



Passing over the processes of manufacture of many kinds of oil of 

 less importance, we proceed to take linseed-oil, or the oil extracted 

 from the seeds of the flax-plant, as an illustration of the manufacture 

 of oil from seeds. " Linseed, rape-seed, poppy-seeds, aud other 

 oleiferous seeds were," Dr. Ure observes, " formerly treated for the 

 extraction of their oil, by pounding in hard wooden mortars with 

 pestles shod with iron^set in motion by cams driven by a shaft turned 

 with horse or water-power ; then the triturated seed was put into 

 woollen bags, which were wrapped up in hair-cloths, and squeezed 

 between upright wedges in press-boxes, by the impulsion of vertical 

 rams driven also by a cam mechanism." In the best mills on the old 

 construction, he adds, the cakes of crushed seeds obtained by this first 

 wedge-pressure were ground anew upon the bed of an edge-mill, and 

 subjected to a second pressure, with the aid of heat. " These mortars 

 and presses," he states, " constitute what are called Dutch mills : they 

 are still in very general use both in this country and on the Continent, 

 and are by many persons supposed to be preferable to the hydraulic 

 presses." 



Owing to the extreme hardness and smoothness of the seeds of flax 

 and hemp, and to the circumstance that the fragment* of their shells, 

 however broken, form minute concavities which will retain the oil 

 unless a greater pressure be applied than could bo given by an ordinary 

 screw-press, the presses employed for extracting oil from such seeds 

 flitler materially from those used in crushing olives and other com- 

 paratively soft oleaginous substances. Hence it is that the wedge- 

 press and Bramah's hydraulic press have been introduced for the 

 purpose. Of these two powerful machines some manufacturers 

 r the former, believing that the same degree of pressure is more 

 nt when imparted by means of sudden impulses or blows upon 

 the end of a wedge, than when it is applied gradually and steadily as 

 in the hydraulic press. In the wedge-press, of which there are many 

 -.ies, the crushed seeds are put into bags of hair-cloth or some 

 similar material, and these bags are then placed between plates of iron 

 united together like the covers of a book, or between boards or blocks 

 of wood, witliiu a very strong and massive framework. The small end 

 of ,1 wedge is then introduced in such a way between the plates or 

 boards that, when it is driven down by the blows of a ram or pestle, 

 it may compress the bags with enormous force. The driving of the 

 wedges is continued until they are so tight that the pestle relumnd 

 from them three times, when they are judged to be sufficiently driven. 

 Th.: use of the hydraulic press instead of this apparatus needs no 

 minute explanation. Some of these act horizontally, the bags being, 

 as in the wedge-press, placed vertically, and separated from one another 

 i>y cast-iron plates ; but in others the bags aru piled upon one another 

 in cast-iron cases, and placed in a vertical press. The seed is put into 

 bag* of flannel or of horsehair. Among other advantages it is stated 

 that the hydraulic or hydrostatic press reqiu'res less space than a 

 stamping-mill which could do the same work, and that tlie hairs ami 

 bags are found to last longer with it than with the old machine. 



A mode much adopted in this country, of obtaining linseed oil, we 

 shall now describe. As the hardness and smoothness of the seed gives 

 it a tendency to nlirle away unbroken under the rolling action ol 

 the millstones by which they are ground, it is desirable, before taking 

 it to the grinding-mill, to bruise or crush the seed by causing it to fal, 

 from a hopper between two iron crushing-rollers, placed side by side 

 and capable of being pressed against each other with any determinate 

 degree of force ; but the use of such rollers is by no means universal 

 the seeds being, in many cases, submitted to the grinding-inill without 

 any such preparation. This mill, which is sometimes called an edge- 

 mill, consists of a pair of stones, technically called runmny-ttona, or 



runners, usually made of granite, resembling grindstones in shape, and 

 rom five to seven feet or upwards in diameter, so mounted as to roll 

 ound in a circular path of small diameter upon a solid horizontal bed 

 of stone or iron laid beneath them. These stones, which roll round 

 ;he bed from thirty to thirty-six times in a minute, are sometimes 

 looped with iron, though many prefer the rough surface of the granite, 

 which may be re-dreesed with a hammer as often as is needful. They 

 p-ind the seed partly by their weight, which often amounts to three 

 ;ons each, and partly by the peculiar rubbing motion which arises 

 rom the circumstance that the outer edge of the stone has to perform 

 x larger circuit than the inner, although the two must of course revolve 

 round the axle at one and the same speed. The action is therefore 

 imilar to that of a cone when forced to roll onward in a straight 

 >ath. The two running-stones are moxmted on the same horizontal 

 axis, but at rather different distances from the central vertical shaft or 

 axis round which they roll, so that they do not follow one another in 

 >recisely the same path on the bed of this mill. The bed is surrounded 

 >y a rim which prevents the seeds from being scattered; and the 

 revolving framework in which the running-stones are mounted carries 

 also two rakes or sweeps, which collect and lay the seeds in a ridge 

 along the circular path of the runners. By this means the seeds are 

 reduced, by the partial expression of the oil, to a pasty mass, from 

 which a limited quantity of very fine cold-drawn oil may be obtained 

 the simple action of the press. 



We have hitherto spoken only of the extraction of the finest oil, 

 without heat. The application of heat before pressing is however 

 necessary for obtaining the principal supply of oil. The precise order 

 of the several operations, as well as the nature of the machinery 

 employed, differs in different manufactories. In some establishments 

 the oil-cakes, or solid contents of the bags, which remain after the 

 first cold pressing, are taken out of the bags, broken to pieces, and put 

 into mortars to be pounded by pestles worked by machinery. There 

 the paste is again broken down, and the parenchyma of the seed 

 reduced to a fine meal ; thus free egress is allowed to the oil from every 

 vesicle in which it is contained ; but it is now rendered much more 

 clammy by the forcible mixture of the mucilage, and even of the fine 

 parts of the meal. When sufficiently heated it is removed to a chauffer, 

 or circular copper-pan ; in which, while it is kept continually stirred by 

 machinery, it is heated to about the temperature of melting bees-wax, 

 either by a charcoal fire, or according to a more recent practice, by 

 steam. It is then, while hot, put into the bags and subjected to a 

 second pressing ; and in some cases the like operations are repeated a 

 third time, by which a further quantity of oil, but of inferior quality, 

 is produced. Sometimes the produce of oil is increased by mixing a 

 little water with the paste ; but this practice is considered to impair 

 the quality of the oil. The oil-cakes which remain alter the last 

 process are used as food for cattle, and for various other agricultural 

 purposes ; but of course the cakes vary greatly in richness according to 

 the degree in which they have been divested of oil. There are small 

 mills in Holland which have no other employment than extracting oil 

 from the cakes which they purchase from the French and Brabauterx, 





Fig. 1. Linseed Crtuhing. 



after passing the process of their mills : a clear indication of the 

 superiority of the Dutch practice over that of their neighbours. In 

 some of the Dutch mills, the produce is increased by the application of 

 moderate heat during the grinding process, by enclosing a little 



