The quantity of oil in the oil tank is shown by gauge glass 44. On the starting of the machine to which the oiler is attached, the pump shaft and the cam disks that it supports are set in motion through worm 24 and worm gear 23. A direct reciprocating motion is given to the pump plunger and to the piston valve by the rotation of the cam disks which have a movement similar to that of the “wobble saw.” The relation of the cam disk is such that the piston valve movements are 90° in advance of the movements of the pump plungers. The pump will run in either direction without alteration. To secure this effect a play of 90° is provided between the cam disk. When cam 22 is driven clockwise, cam disk 20 is driven by the lug which meshes with a lug on disk 22. The cams are then in such a relation that the cam valve disk is 90° in advance of the pump cam disk. When reversed, cam 20 remains at rest until cam 22 catches the lug and cam 20, when the drive continues as before. The cams are then in the same relation as previously for as the valve disk 22 has traveled through 180° it is evident that it is 90° in advance of the pump disk. (119) Castor Oil for Aero Engines. Castor oil is used almost exclusively in the Gnome and other rotary engines of the same type, but has not been particularly successful on stationary cylinders. Chemically, castor oil differs from all other vegetable or animal oils in containing neither palmitin or olein. It is soluble in absolute alcohol, but practically insoluble in gasoline. On the other hand, the castor oil is capable of dissolving small quantities of mineral oil, the more fluid they are the less it absorbs of them. But the insolubility of castor oil in mineral oil disappears completely when it is mixed with even a very small quantity of another vegetable or animal oil, such as colza or lard oil. An adulteration may thus result in a serious reversal of the oil’s best qualities; in fact, in serious seizures, Castor oil does not attack rubber, but it contains 1 to 2 per cent of acid fats; sometimes more.