~81. The Relative Viscosity of Oils~ is determined in several ways. Various machines have been devised for testing the lubricating properties of oils, but as the cheap ones are of no use, and as those which are reliable are so expensive as to prohibit their general use except in laboratories and large factories, a simple method of ascertaining the relative viscosity of oils is desirable. The author used a piece of plate glass of suitable size on which one drop of each oil to be tested was placed near its end. The glass inclined from the horizontal, longitudinally--the angle of inclination being 6 degrees--and was placed in a constant temperature of 15.5° C. (= 60° F.) The total distance in centimeters which each had traveled by the end of each day, as well as the appearance of the "track" which it had left is shown in table VII. TABLE VII. RELATIVE VISCOSITY AND GUMMING OF OILS. Temp. 15.5° C. = 60° F. Inclination 6 degrees. Time 7 days. ----------------+---------------------------------------+----------- SYMBOLS | DISTANCE IN CM. | ACCORDING TO | TRAVELED BY OIL AT THE END | WIDTH TABLE III. | OF EACH DAY. | OF | | TRACK. ----------------+----+----+-----+-----+-----+-----+-----+----------- DAYS. | 1 | 2 | 3 | 4 | 5 | 6 | 7 | ----------------+----+----+-----+-----+-----+-----+-----+----------- E. K. w. |16 |18 |Stat.| ... | ... | ... | 18 | Medium. W. F. N. w. |15 |16.5| 18 | 19 | 20 |Stat.| 20 | " W. C. w. |17.5|19 | 20 |Stat.| ... | ... | 20 | Narrow. B. & K. w. |12.5|15 | 17.5| 20 |Stat.| ... | 20 | " C. L. Co. w. | 7.5|10 | 12.5| 15 | 17.5|Stat.| 17.5| Very wide. C. L. Co. No. 1.|15 |16.5| 18 |Stat.| ... | ... | 18 | Medium. Glyc. |15 |16.5| 18 |Stat.| ... | ... | 18 | " Sp. | 0 | 2.5| 5 | 7.5| 9 | 10 | 11 | Narrow. Ol. | 5 | 6.5| 7 |Stat.| ... | ... | 7 | " ----------------+----+----+-----+-----+-----+-----+-----+----------- Table VII not only shows the relative viscosity of the various oils, but also their tendency to gum or dry (79.) The "width of the track" left by the oil is an indication of the cohesion (20) and adhesion (21) which exists, respectively, in the oil and between the oil and the glass. A narrow track denotes great cohesion and little adhesion; a wide track denotes great adhesion and little cohesion; while a medium track indicates that both properties are more nearly equal. If an oil possess great adhesion and little cohesion it is more liable to resist the tendency to be squeezed out of bearings, but it is also more likely to spread. Another test made in the manner just described (table VII) gave results as shown in table VIII: TABLE VIII. RELATIVE VISCOSITY AND GUMMING OF OILS. Temp. 24° C. = 75° F. Inclination 7 degrees. Time 7.3 days.