In the first place, considerable salt is used in the material, more or less of which is left in the oil. When the melted fat is drawn off into the seeding trucks and is left to stand for three or four days, this salt attacks the iron, and if not watched very carefully small pin-holes will be eaten through the iron, the result being that the galvanized iron pan will leak into the wooden box proper. Again, every time the seeding trucks are emptied, they are thoroughly washed and steamed out and more or less of this water for washing finds its way in between the lining and the wooden box. When the seeding truck is filled with oil, the weight of the oil causes this water, which is held between the iron and the wood, to ooze into the oil, causing “sour bottoms.” This particular point has caused the loss of a great many thousands of dollars in the manufacture of this product, even though it is apparently a very unimportant matter. =Manufacture of Wooden Trucks.=--In using wooden seeding trucks, attention is called to a very important item to be considered, and if not carefully looked after the results will be unsatisfactory. The oil is drawn into seeding trucks at a temperature of about 120° to 125° F., which will shrink wood very rapidly, therefore the trucks should be made out of thoroughly kiln-dried lumber, which should be _extra_ kiln-dried. The bottom and sides of the truck are bolted together with a bolt running through them and one on either end, so that any shrinkage of the wood can be taken up. The same is true of the sides of the truck. In each of the joints, after they are perfectly made, a strand of wicking should be put in between the edges, so that when it is drawn down it forms a perfect packing. As is well understood, the shrinkage of wood is mostly crosswise of the grain, there being very little lengthwise; thus it will be seen that the wood in these trucks, both at the sides and at the ends, must be put in so that it will all shrink uniformly. The bottom of the truck will naturally shrink sidewise and if the bolts are drawn up it stops the opening, while if the sides of the truck shrink, the bottom bolts can be drawn up, readily stopping the leak. The ends of the truck must have the grain running up and down instead of crosswise, for if the bottom of the truck joins sidewise and the end pieces are running crosswise of this grain, it will be impossible to draw the bottom up tight, on account of the lack of shrinkage of the ends where the grain runs lengthwise of the end. [Illustration: FIG. 57.--KNUCKLE TYPE OLEO OIL PRESS.]