The tempering or cooking of the crushed seed having such an important bearing on the yield of oil has also suffered many changes. There was considerable variation in the tem perature used, from cold to hot, according to the manufacturer. Often the spontaneous heat of the crushing was considered sufficient. In the tamper of the Dutch mill water was played on the meal in the mortar, when vapors began to arise, in order to keep it from getting too hot and thus spoiling the oil. No further tem pering was considered necessary. Later, how ever, and notably in connection with the muller stones regular cookers began to be used these were heavy sheet iron drums or tanks, slowly revolving over a charcoal fire until the proper temperature was attained. With the advent of the hydraulic press, improvements were made in cooking devices and stationary heaters be gan to be used in which the meal was cooked by steam. Up to the year 1856, and as related, the cooked meal was placed in the bags by hand; at this date, however, a device was patented to form the cooked meal into soft cakes or molds preparatory to placing them into the cloth or wrapper which was to take the place of the bags originally used. This was considered a great boon, saving as it did the laborious process of handling and molding the meal by hand to fit the press; though some what clumsy at that time, the "molder)) or f or me has been much improved. Where in former years the molder was run by power from the shaft, now hydraulic pressure is utilized, and the "former)) is in reality a minia ture press, consisting of a square mold or box into which a plunger presses the required amount of meal. Very light pressure is suffi cient, and it is so arranged that the cooked meal will not 'be compressed to the point where the oil is separated.
The tempering, crushing and pressing of linseed was carried on, with a few exceptions, substantially as related up to the year 1878, when the most lasting improvement to oil• machinery was made, and which introduced practically the system in use at the present time; namely, the automatic "Lawtherp process. Greater economy was immediately secured and larger yields of oil. The old muller stones and cracker rolls gave way to the stack of "four or five chilled iron rolls, by means of which the seed was bruised three or four times in passing through. Apparatus for controlling and regulating the high pressure was intro duced; kettles or cookers were steam jacketed and had larger heating area, and steam was fed into the meal to moisten as well as heat it. The plate press had also been given the pref erence over the box press, which was clumsy. Although the very best mills to-day have some improvements over the original Lawther process, they make rather toward greater economy than increase of yield. The modus operandi in the largest and most complete mill to-,clay is as follows: The flax seed. is first thor oughly cleaned by separators and dust collectors until the original dirt, amounting to 10 or 20 per cent, has been reduced to less than 1 per cent. This seed is now passed through the
rolls, there being about one set of five rolls high to every three presses. The crushed seed falling from these rolls is led by screw con veyors into the steam jacketed cookers of large capacity and bolding a considerable quantity, where it is tempered. This consists of heating the ground seed to a temperature of from 120° to F., according to the quality of the seed used, and moistened with live steam, all the time being kept in constant motion to prevent burning. When the temper is considered per fect a batch is made. This consists of draw ing off the cooked meal on to the formers and molding the cake. A piece of cloth somewhat wider than the molded cake is placed so that the tempered meal may be drawn out onto it. This cloth or wrapper, as it is called, is a sub stitute for the horse hair cloth and woolen bags of former days, but now made of pure camel's hair to stand the high heat and enormous pres sure. By a single motion the former is now closed and immediately reopened, when the ends of the cloth protruding are automatically wrapped around the soft cake and it is placed in the press (by automatic nippers, in the Lawther press). The batch makes 20 of these cakes, which fills one press. The pressure is now turned on by an automatic valve or change cock which slowly increases the pressure up to about 4,000 pounds to the square inch. This enormous pressure is generated by very power ful hydraulic pumps, connected to what is known as the accumulator system, the first pres sure being up to 800 pounds per square inch and the second from 2,600 to 4,000 pounds. The accumulators are for two purposes; first, to act similar to a safety valve on a boiler, preventing the pressure from exceeding the limit ; secondly, keeping the pressure at a steady level through out the time the seed is in the press. Before the adaptation of the accumulator and change cock, the oil was pumped directly into the press, causing an unequal flow and consequent re duction in the yield of oil. Six presses are generally grouped, one being emptied and re filled every 10 minutes, the six thus completing one hour in time and allowing each press in the group to drain every 50 minutes. In some mills seven batches are made instead of six, and the weight of the cake is also increased from 11 and 12 to 14 pounds. This is done in order to increase the capacity of the mill, but generally at a sacrifice in the percentage of oil. As each batch is removed from the press, the camel's hair cloth wrapper is stripped off, the rough edges of the cake trimmed automatically, and the cake piled up in the cake house, where it is allowed to dry for at least 48 hours. The raw oil, after having been run from the settling troughs at the back of the presses, is carefully filtered and placed in tanks ready for barreling.