as high a flashpoint as possible so that they will not be vaporized from the cylinder walls as soon as they come in contact with the hot products of 'combustion.

Q. How is the fire test made?

A. The fire test of the oil is really a continuation of the flash test and is shown at Fig. 114. The fire test is the point indicated by the thermometer where the oil becomes sufficiently heated so not only the vapors flash momentarily but the entire mass of oil takes fire.

Fig. 114.-Simple Method of Making Fire Test of Lubricating Oil.

Q. What is the cold test and what does it indicate?

A. The cold test is made as indicated at Fig. 115 and is useful in showing the point at which oil will coagulate or become so stiff that it will not flow. This is easily performed by putting a flask of lubricant in a freezing mixture of ice and salt and inserting a thermometer to indicate the point at which the oil becomes solidified. An ordinary form of temperature indicating thermometer may be used in making this test. A suitable oil for winter use should

not stiffen enough at zero temperature to prevent its reaching the bearing points.

Q. Name simple ways to determine presence of adulterants. A. The presence of animal fats in greases can be quickly determined by exposing a quantity of the suspected grease to the air.

If the grease turns ranIcid and has a foul smell this may be considered a good indication that organic adulterants are present. The presence of fats in oils may be determined by the saponification test which consists of heating a quantity of lubricant under suspicion with potash and stirring briskly till the alkali is well absorbed by the oil. If the surface of the oil is covered with soapy matter after cooling it indicates the presence of animal fats in quantities proportionate to the amount of soap. In any mixed oil in which mineral and animal lubricants are combined,

there is considerable

fat which will decompose liberating fatty acid if used in the cylinder and there is also the danger of charring the fat and augmenting the proportion of carbon deposits in the combustion chamber.

Q. What are specifications of a suitable cylinder oil?

A. The oils used for cylinder lubrication should preferably be

distilled in a vacuum in order that the light distillates, such as the fuel oils, will be separated from the crude petroleum base obtained from Pennsylvania wells at low temperatures and then filtering the oil through charcoal to remove free carbon and other impurities it contains. The greater the number of times the oil is filtered the lighter it becomes in color and body. The best cylinder oils are obtained in three grades: light, which has a consistency slightly greater than machine oil; medium, which is somewhat heavier than the light and is an intermediate grade between that and the heavy bodied oil which has the consistency of warm molasses. The light and medium oils are used on power plants having closely fitting pistons and bearings, while the heavy lubricants are used in air cooled engines and in power plants that have become worn to such an extent that the cushioning properties of the heavier bodied oils are desirable. Any pure hydro-carbon oil, having a high degree of viscosity at 100 degrees F., having a vaporizing point of about 200 degrees F., a flash point between 425 and 500 degrees F., and a fire test of 600 degrees F. or over, will be suitable for use in gas engine cylinders.

Q. How are the various portions of an automobile lubricated? A. The power plant of an automobile is usually lubricated by some means that will insure a continued supply of lubricant to the interior parts of the engine and that will supply the oil in quantities that will compensate for any loss through vaporizing or burning in the combustion chamber or leakage. The change speed gearset, differential gearing, universal joints and axle bearings are generally packed with a semi-fluid grease that remains in place and that does not need renewing frequently. Spring shackles, brake rod ends, and similar parts are greased by compression grease cups, which may be screwed up from time to time to inject more lubricant between the bearing surfaces or by means of small oil cups which demand periodical attention and filling from the usual form of hand oil can or syringe.

Q. Describe simplest method of oiling gas engine parts.

A. The interior of gasoline engines of the closed base form may be oiled by putting in a certain quantity of lubricant in the engine base

until it rises to such a height that it will be splashed around the inside of the motor by the revolving connecting rod lower end or by counter weights or enclosed flywheel. On open base engines (never used in automobiles) the main bearings are lubricated by compression grease cups in many cases and the connecting rod by oil from a small sight feed oil cup directly attached to the crank pin bearing. A similar member of larger capacity serves to oil the piston and cylinder walls. The open base form of motor is never used in automobile practice though it has received wide application in the stationary power plants and is used to some extent in marine service.

Q. What is a sight feed lubricator?

A. The gravity sight feed lubricator is seldom used at the present time in automobiles. The first sight feed devices included a container for the lubricant having glass walls, so the amount of oil it held could be readily ascertained at any time, communicating with a lower chamber, also having glass walls, by means of a needle valve controlled orifice. The valve could be adjusted to feed any desired number of drops of oil per minute and the flow of oil could be stopped at will without changing the adjustment of the needle valve by shifting a small lever that allowed the valve to drop under slight spring pressure until it closed the passageway communicating to the small sight feed chamber beneath the main container which was piped to the point needing the lubricant. As a general rule gravity oil cups are applied directly to the parts needing oil and are generally used on cheaper marine and stationary engines. Q. What is a compression or pressure feed lubricator?

A. A typical pressure feed lubricator is outlined at Fig. 116. This consists of a small tank holding one or two quarts of oil, which is attached to the motor at any convenient point and which is designed so the oil it contains may be put under pressure and forced through a pipe to a sight feed manifold fitting from which the individual oil leads go to the points needing oil. The pressure is usually obtained from the exhaust or by a pipe leading to the crank case interior. A small check valve fitting is carried at the end of the pressure pipe on the oil container in such a way that the air or gas under pressure will raise the check valve from its seat and flow

into the oil container. of gas in the tank is sufficiently high the confined gases cannot escape and must force the oil out of the tank. The oil flows to the top of the sight feed arrangement where the amount dropping can be regulated at will and as the manifold is always carried higher than the bearing point the oil flows principally by gravity assisted to some extent by a slight pressure escaping from the oil container. As a lubricator of this nature will supply lubricant as long as there is pressure in the tank and as no oil is needed after the engine

As the check valve seats when the pressure

stops it is desirable to fit the container with a small petcock or relief valve which can be opened when the engine is stopped to relieve the pressure on top of the oil and thus interrupt the supply to the bearings.

Q. Name principal methods of mechanical oiling and state their advantages.

A. There are two main methods of oiling a power plant by mechanical means, the most common one involving a single pump which keeps the oil in circulation from the oil sump or container integral