VOL. II.OIL-TESTING MACHINE.PLATE X.
Fig. 2501.
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Fig. 2502.

“Testing for Salts and Acids, etc.—It will be obvious that however good as a lubricant an oil is, and however valuable its properties may be when examined, if it possesses any corrosive quality which will be injurious to the metals upon which it is placed, it will soon become detrimental to the machinery, and may also cease to be valuable as a lubricant. Mr. William Thomson, analytical chemist, of Manchester, read a paper on this subject at the British Association at Glasgow, and he stated the results of elaborate experiments conducted by him to discover the influence of various oils of commerce upon bright strips of copper. He permitted the copper strips to remain entirely covered by oil. He also conducted similar tests with half of the strip below the surface of the oil, and the other half exposed to the atmosphere, in order to see what influence the oil had, when the surface line touching the metal would, of course, be acted on by the atmosphere. After noticing the effect upon the brightness or dulness of the copper, he carefully tested the oils in order to detect the quantity of metal which had been dissolved. Mr. Thomson found the following oils dissolved the largest proportions of copper, leaving the surfaces of the copper slips bright—rape, linseed, sperm, raw cod-liver, Newfoundland cod, and common seal oils; and that the following dissolved much smaller proportions of copper, also leaving the slips bright—seal, whale, cod, shark, and East Indian fish oils; and that mineral oils seem to have no dissolving power on the copper, the only effect being a slight discoloration on the copper slip of a greyish color.

“Swiss Watchmakers’ Test for Fluidity and Capacity to Resist Cold.—It seems, according to the Watchmaker and Jeweller (a monthly trade journal), that the plan I have described, and what may be called the warm glass test, seems to be looked upon with favor for testing oil in Switzerland. The degree of heat used for testing the fluidity of oil is 200° Fahr., and if this causes the oil to become a varnish two or three days after the test the oil is considered unfit for use. Another test is one to which I have not alluded, and that is, capacity to resist low temperatures. Oils are tried for their capability to withstand low temperature in the following manner: Fifteen parts of Glauber salts are put into a small glass vessel, a small bottle of oil to be tested is immersed into this; this done, a mixture of five parts of muriatic acid and five parts of cold water is placed over the salt. By means of a thermometer the temperature is indicated, and when it shows a very low temperature, the behavior of the oil, subject to this freezing mixture, may be observed and noted. Mr. Thomson, however, considers that this mixture is not so good or so cheap as ice alone, or a mixture of ice and common salt.

“Blotting-paper Test.—It seems it is considered that the blotting-paper test for fluidity is more reliable, according to the writer of the article, than the inclined plane experiment. In order to use this test we must saturate the strip of blotting-paper with oil, and watch whether the drops fall off in pearls or have an inclination to spread out. The latter is a certain sign, the writer says, of a viscid oil. Although this may be considered viscid oil, and may not be valuable for watches, it may, however, be a good oil for heavier machinery.”

The amount of friction between a journal and its bearing varies with the kind of metal of which the journal and bearing are composed; on the area of surface in contact in proportion to the load or pressure sustained by the bearing surfaces; on the nature or degree of the lubrication afforded; on the diameter of the journal in proportion to its length; on the manner in which the journal fits or beds to its bearing, and on the kind of motion, as whether the same be continuous, intermittent, rotatory, or reciprocating.

Referring to the friction as influenced by the nature of the metals in contact: the friction varies with the hardness of the metal; thus, with hard cast iron, there will, under equal conditions, be less friction than with soft cast iron. The friction is greater when the surfaces in contact are both of the same metal than when they are of different metals. Mr. Rankine summarizes General Morin’s experiments on the friction of various bodies not lubricated as follows:—

GENERAL MORIN’S EXPERIMENTS ON FRICTION.

Surfaces.Angle of
repose.		Friction in
terms of the
weight.
degrees.
Wood on wood, dry14 to 261⁄2.25 to .5
„ „soaped111⁄2„2 .2„.04
Metals on oak, dry261⁄2„31 .5„.6
„ „wet131⁄2„141⁄2.24„.26
„ „soapy111⁄2 .2
„ elm, dry111⁄2„14 .2„.25
Hemp on oak, dry28 .53
„ „wet181⁄2 .33
Leather on oak 15 „191⁄2.27„.38
„ metals, dry291⁄2 .56
„ „wet20 .36
„ „greasy13 .23
„ „oily81⁄2 .15
Metals on metals, dry81⁄2„111⁄2.15„.2
„ „wet161⁄2 .3
Smooth metal surfaces occasionally greased4 „41⁄2.07„.08
„„„continuously greased3 .05
„„„best results13⁄4„2 .03„.036
Bronze on lignum-vitæ, constantly wet3(?).05(?)

“The ‘angle of repose’ given in the first column is the angle which a flat surface will make with the horizon when a weight placed upon it just ceases to move by gravity. The column of ‘friction in terms of the weight’ means the proportion of the weight which must be employed to draw the body by a string in order to overcome its friction, and the proportionate weight is sometimes called the coefficient of friction.”[34]

[34] From Bourne’s “Handbook of the Steam Engine.”