shaft, the friction at first is considerably greater than it is after running a short time, which, as Mr. Tower says, is probably owing to the change in the direction of surface fibers of the metal. After reversing, observations were again taken every ten minutes during the next run of one hundred minutes. These two runs constituted an experiment of two hundred minutes with 100 pounds per square inch. The machine, oil, and bearing were allowed to cool for the next experiment, which was made with the weight increased to 150 pounds per square inch, or a total weight of 1,500 pounds. Each experiment was made by increasing the weight by 50 pounds per square inch, precisely as above described, till the limit of the capacity of the machine was reached. The difference of the readings of the scale for the two runs of one hundred minutes each gives the whole angular movement of the pointer, due to friction of the test metal on the journal and the viscosity of the thin film of oil between the metal and the journal. At the same time that the readings of the scale were taken, the revolutions per minute and the temperatures of the oil bath, the metal, and the air in the room were also taken.

Each metal was tested in precisely the same manner and with the same quantity of sperm oil as a lubricant. Table C gives the tabulated results of the two Magnolia metals, Nos. 1 and 2, and the "A" white brass, with increasing weights of 50 pounds per square inch.

The results of Table C were checked, approximately, by reversing the process of the change of weights and by running the machine for ten minutes in each direction for the Magnolia metals and twenty minutes for the "A" white brass. The data were taken as before, for each decrement of 50 pounds per square inch. The "A" white brass must be run a longer time than the Maguolia metals to bring the friction to the lowest amount, for a given change of weight on the wearing surface, and for this reason, the machine was run twenty minutes each way for the "A" white brass, instead of ten minutes, as for the Magnolia metal. Table D gives the results of the tests with each metal. Finally, the three metals were tested in the same manner, as above described, but with water as the lubricant and the machine operating for sixty minutes. In this experiment it was deemed best not to exceed 200 pounds per square inch for the "A" white brass, on account of its heating and requiring frequent change of water in the pan, for fear of injury to the steel shaft before the Magnolia metals were tested; besides, the machine would not turn successfully with any weight above 200 pounds per square inch. Magnolia metal No. 1 was tested up to 600 pounds per square inch, the temperature not rising high. Usually, clean water was used only after each run ahead and reverse for every change of weight, but in the case of the "A” white brass, the water had to be renewed several times to keep the temperature as low as possible. Table E gives the results of these tests.

As to the value of the "A" white brass and Magnolia metal for shaft bearings, the Board arrived at the following conclusions:

(1) Magnolia metal having plumbago in its composition is much superior as an anti-friction metal to the "A" white brass.

(2) As a lining for brasses they should both be used in as thin a body as will remain fixed in place, about three-eighths or one-half inch thick, and in slabs or surfaces as large as possible.

(3) The metals should not be overheated in melting. In the case of Magnolia inetal it should be heated sufficiently to just scorch the soft pine stick with which it is stirred.

(4) Magnolia metal should be cooled quickly or poured into as cold a receptacle as is possible, in order to maintain an equal distribution of the graphite throughout the

mass.

(5) To obtain the best results with Magnolia metal, it would be best when pouring it into a brass around a journal or mandrel to have the brass above the mandrel and in proper position. Poured in this way, that portion of the metal which contains the largest quantity of precipitated graphite will be the wearing surface. The mandrel should be made quite warm, so as not to chill the metal too suddenly at the wearing surfaces.

(6) In whatever way Magnolia metal is poured, it should not be flush with the metal of which it is a lining, but stand above it from one eighth inch to three-sixteenths inch when finished, and should be lightly pened or expanded, so as to fill the recesses well and retain the lining firmly in place. This should also be the case with the "A" white brass. Prolonged or heavy pening is not recommended.

(7) From the fact that the "A" white brass becomes soft and easily disintegrates at a temperature much below its melting point, it is useless as a bearing material when that temperature is reached.

(8) Magnolia metal operates better than the "A" white brass with water as a lubricant, the difference between its friction qualities, with water and with oil as lubricants, not being so marked as in the case of the "A" white brass under the same conditions.

(9) Magnolia metal requires less lubricant than the "A" white brass. (10) It was recommended for use in the machinery of naval vessels.

11294—N 88————26

"A" white brass fused at 360°. Temperature of magnolia, 386°.

NOTE.-The temperatures were taken every minute. The results in each line are the means for each change of weight.

NOTE.-The experiment of January 17, being of a preliminary character, is not entered in the summary.