When small numbers of animals are being fitted for show, a movable fence can be used and a small patch pastured at a time. A diagram of hurdle and panel for such a fence is shown in Fig. 767. In Fig. 766, the hurdle is shown in use. It some times happens that stock do not at first relish the rape, but all eventually learn to eat it and when once started eat it voraciously, cases being known when swine have even dug out the roots and eaten them. [For fuller discussion of comparable methods and results, consult the article on Soiling.] It should be understood that, while very fattening, rape cannot be depended on as a single feed properly to fatten animals, but must be used in conjunction with a grain ration. Flesh made by feeding rape alone is likely to be soft and blubbery, and not of the firm handling qualities to suit either the stock judge in the show ring or the butcher on the block. [Further consideration of the feeding value of rape and other products may be expected in Vol.
When cut for soiling, rape should be fed soon after cutting, for if left until badly wilted it loses its palatability. If not cut closer than four inches from the ground, it was found at the Wisconsin Experiment Station that three crops could be secured in a good year, yielding a total of thirty six tons of feed to the acre.
In a favorable season, stock may be turned on the rape in about six weeks from the time of planting, but more often it takes eight weeks for rape to reach the best or most satisfactory feeding stage.
Manufacture of oil.
There are or have been several ways of crushing the seed for oil, and many machines have been con structed for each process. The early method was by use of a stamping mill in which the seed was run into mortars and crushed by means of stamp ers. This was a cumbersome process and gave way to the roller system, in which the seeds were run between rolls set at proper distances. The early system of rolling did not crush the seed fine enough and it was necessary to recrush by means of mill stones or runners. This method also proved too costly and cumbersome, and was replaced by a machine in which were three sets of rollers. Each set was a little closer than the preceding, and the crushed seed passed from one to the other until, after passing the third set of rolls, it was in proper condition to go into the presses.
It was found later that the extraction of the oil was facilitated by heating the crushed seed before putting it into the presses. Enough of the pulp
was placed in a shallow pan to make one cake—nine to eleven pounds. These pans were exposed to heat varying from 167° Fahr. to 176° Fahr., but never to 212° Fahr., as this would have damaged the oil. In the modern process of heating, the pulp is steamed to the required temperature.
Many styles of presses have been used, but all the more modern presses are operated by hydraulic power and are composed of several pans so ar ranged that pressure can he applied all at once. Experience has shown that a more thorough ex pression of the oil can be made when cakes are in separate pans than when several cakes are placed one on another in the same press with only the cloths between. The material for each cake is placed in a cloth so cut that the ends when folded overlap, making a perfect case. The cloths are composed of linen on one side and wool on the other, with ropes sewn between the two at inter vals, thus giving the scalloped appearance to the cakes. The cakes are submitted to a pressure of 2,840 pounds to the square inch and the process of oil expression requires fifteen minutes. After the pressure is removed, the cakes are taken from the press and the edges trimmed on the assumption that the oil has been completely removed at the center of the cake, but has not from the edges. The material cut from the edges is mixed with a new lot and repressed.
The oil runs into a collecting reservoir from which it is pumped into a 2,000- gallon tank. From here the crude oil is pumped either into barrels for crude oil use or into refining reservoirs. In refining the oil it is exposed first to a heat of 86° Fahr., in an open vat to which per cent to 1 per cent of sulfuric acid is added with continuous stirring. In stirring, a vertical movement is preferable to a horizontal or rotary motion. From the heating vat the oil is run into a tank and washed several times with hot water, and then into a vat where 5 per cent of common salt is added and the oil left until, with the aid of the salt, it has become completely clarified. For the purest oils, suitable for table use, a filtrating process is resorted to in which the oil is run through successive layers of linen tow and moss.
Refined oil should be of a pale yellow color, clear, free from acid and without any rancidity. It should burn with a clear white light without soot or odor. Such oils are used for lights and, when specially treated, for table and cooking purposes.