A simple method for testing the purity of castor oil is at the disposal of all. It is known as the Finkener test. Ten cubic centimeters of castor oil is placed in a graduate. Five times as much alcohol, 90 per cent, is added and stirred in. The solution should remain clear and brilliant at 15 to 20 degrees C. An admixture of foreign oils, even if only 5 per cent, riles the solution at this temperature, though not above it. (120) Force Feed Troubles. The most common trouble with force feed systems is the failure of the operator to remove the dirt collected by the strainer. The oil piping should be cleaned out at least once every year by means of a wire and gasoline, to remove any gum that may have been deposited. Driving belts should be kept tight to prevent slipping, and belts that are soaked with oil should be cleaned with gasoline and readjusted. Leaking pump valves generally of the ball type are a common cause of failure. They may leak because of wear or by an accumulation of grit and dirt on their seats, which prevents the valves from seating properly. If the valves leak, the oil will be forced back into the tank, or will not be drawn into the pump cylinder at all, depending on whether the inlet or discharge valve is the offender. Plunger leakage which is rare will cause oil failure. If the oil pipes that lead to the bearings rub against any moving part, or against a sharp edge, a hole will be worn in the pipe, a leak caused which will prevent the oil from reaching the bearing. A dented or “squashed” pipe will prevent the flow of oil. The set screw or pin holding the pulley to the pump shaft may loosen and cause it to run idly on the shaft without turning the pump. This will of course, prevent the circulation of oil. The worm and worm wheel may wear so that the pump is no longer driven by the pulley shaft, or a poor pipe connection may leak all that the pump delivers. The amount of oil required by each lead or bearing should be carefully determined by experiment, and kept constantly at the right number of drops per minute. The feed adjustments jar loose, and should be inspected frequently. (121) Oil Cup Failure. Oil cups should be cleaned out frequently with gasoline or kerosene, as any gum or lint will interfere seriously with the feed. They should be adjusted and filled frequently to prevent any possible chance of a hot bearing. Oil cups should be as large as possible in order that they may be left for considerable periods without danger of a hot box. Cold weather affects the oil feed to a considerable extent, especially with small oil cups, and they should be kept as warm as possible. When heavy oils are used a cold draft will stop the feed. Oils may be made more fluid in cold weather by the addition of about ten per cent of kerosene. (122) Hot Bearings.