FRICTION AND LUBRICATION 273 
“minute, the coefficient of friction at a temperature of 120° Fahr. was . 
only one-third of what it was at a temperature of 60° Fahr. 
The following figures show the comparative friction with various 
lubricants tried by Mr. Tower under as nearly as possible the same condi- 
tions :—Temperature, 90° Fahr. Lubrication by oil bath—sperm oil, 
0484; rape oil, 0°512; mineral oil, 0°623; lard oil, 0°652; olive oil, 
0°654; mineral grease, 1048. These figures are the means of the actual 
frictional resistances at the surface of the journal (4 inches diameter) in 
Ibs. per square inch of bearing at a speed of 300 revolutions per minute 
(314 feet per minute), with all nominal loads from 100 to 310 lbs, per 
square inch. They also represent the relative thickness or body of the 
various oils, and also in their order, though perhaps not exactly in their 
numerical proportions, their relative weight-carrying power. Thus sperm 
oil, which has the highest lubricating power, has the least weight- 
carrying power, and though the best oil for light loads, would be inferior 
to the thicker oils if heavy pressures or high temperatures were to be 
encountered. 
239. Work Lost in Priction in Journal Bearings.—Let R = resultant 
load on journal in Ibs., d@=diameter of journal in inches, V = surface 
velocity of journal in feet per minute, N =revolutions of journal per 
minute, ¢ = friction angle, and y= coefficient of friction. 
The moment of R is $Rd sin ¢, which may be written }Rdp, since > 
is a very small angle. The work done per minute on friction is therefore 
Bene RV ft.-lbs. The horse-power lost in friction is te 
240. Methods of Lubricating Bearings.—There are two principal 
methods of lubricating bearings. In one method the oil is allowed to 
flow in at ordinary atmospheric pressure, while in the other the oil is 
forced in under sufficient pressure, generally by a pump employed for 
that purpose. When the oil enters at atmospheric pressure it should be 
delivered to the bearing at the place where the pressure on the bearing is 
least, but with forced lubrication the oil should be delivered to the bearing 
at the place where the pressure is greatest. 
The well-known needle lubricator is shown in Fig. 415. B is an 
inverted glass bottle or reservoir containing oil. §S is a wooden stopper, 
one end of which fits into the neck 
of the bottle, while the other end fits 
into a hole over the bearing of the 
journal J to be lubricated. N is the 
needle, which fits loosely into a hole 
in the stopper 8. The lower end of 
the needle rests on the journal. 
When the shaft is at rest capillary 
action prevents the oil leaving the 
bottle, but when the shaft is rotat- 
ing the vibration set up causes the 
oil to flow slowly on to the journal. _ 415. . 416. 
tee Gatipy sta . oat 22 
piece of wire flattened at its upper end to prevent it falling out when 
the lubricator is removed from the bearing. 
A syphon lubricator is shown in Fig. 416. The oil is stored in the 
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