gether with the springs from the driving wheel 9 by means of the female screws z forming a worm-wheel and the cross shaft s provided with screw-threads. By this means the load can be entirely removed from the journal-boxes. On the lower shaft there is further the driving wheel G, as well as a screw by means of which the motion of the shaft is transmitted to a counter. Besides the pointers, which indicate the number of revolutions, this counter also sets in motion the pointer t, which indicates upon the scale u the approximate velocity of the rim of the wheels in kilometers per hour. The two friction-wheels cc are turned eccentrically about 2.5 millimeters so that in revolving there is a slight vertical oscillation, which is transmitted to the upper wheels, thus imitating the jolting of the cars upon the track.

In executing the test the lubricant under trial is brought into the journal-boxes m m. The spring is then raised to remove the load as much as possible from the upper shaft, and the lower shaft set in motion. When the apparatus is running the springs are gradually lowered, and finally loaded with a weight corresponding to the intended use. The oil which with this test stands the heaviest load at the greatest velocity without heating the journal-boxes is to be considered the best.

Although the apparatus does not allow of accurately measuring the frictional resistance, the practical value of lubricants is fairly determined by it. It especially furnishes sure guiding points whether, with determined loads and velocities, hot running of the axles is to be feared or not, which is of great importance as regards the use of oils for railroad purposes.

Professor E. Willigk's oil-testing machine. This apparatus differs from the preceding chiefly in the choice of journals and in that during the experiments special regard is had to the temperatures. It consists of a vertical shaft bedded in the bottom plate of a cast-iron frame and revolved by a gearing. The shaft carries on its upper portion a hollow cup-shaped cone which forms the bearing of the test-arbor. The latter forms another hollow cone of tombac which is fitted to the first so that

it sits exactly upon its bottom. By means of a weighted lever the test-arbor can be loaded at will within certain limits. The inner space of the test-arbor is filled with mercury into which dips the thermometer for observing the temperature.

A small portion of the oil to be tested is brought into the lower part of the cone forming the bearing, and the machine set in motion.

The quality of the lubricants is tested either by lubricating the test-bearing with a determined quantity of oil and counting the number of revolutions the machine makes until the bearing has acquired a certain temperature; or the machine is allowed to make the same number of revolutions and the temperature which the test-bearing acquires with the use of various oils is observed. With the first method the better lubricant is indicated by the greater number of revolutions, and with the latter, by the lower temperature.

The results yielded by the second method suffice for practical purposes, but it is better to use, instead of a counter, a watch with a second-hand, and determine the increase in the temperature by allowing the apparatus to revolve for the same. length of time at the same velocity with each kind of lubricant.

The chief object of the use of a lubricant is to decrease friction by enveloping two metallic surfaces rubbing upon each other, in order to gain work as well as to prescrve the surfaces in good working condition.

These general guides, on which depends the choice of a lubri cant, also prescribe the course the examination or test has to take. Generally speaking, an examination will, therefore, have to deal with answering the following two principal questions:1. Does a lubricant intended for certain purposes possess in a sufficient degree the ability of decreasing friction between two metallic surfaces?

2. Has the respective lubricant the capacity of resisting, in a degree corresponding to a certain purpose and for a sufficient time, the effects of the work it has to perform?

With these conditions in view, R. Jähns, inspector of ma

chinery of the railroad management at Cologne, has recently constructed and patented a very ingenious and useful apparatus, which is very likely to be introduced upon all German FIG. 173.