LUBRICATION

277

already discussed (pages 155-160) is not without interest in this
connection.

Although hexane, diallyl, benzene, and hexamethylene differ
in fluidity by more than 250 absolute units at a given tempera-
ture, they all boil within 20 degrees of each other, hence the
fluidity-vapor pressure curves for these hydrocarbons are very
distinctive, as shown in Fig. 89. If a low vapor pressure for
a given fluidity is an advantage, on the assumption that an oil
should not volatilize off from the walls of an engine cylinder or
away from an overheated bearing, then straight chain hydro-
carbons have the apparent advantage. On the other hand, if
low vapor-pressure and high molecular weight for a given fluidity
result in a tendency toward carbonization, then cyclic com-
pounds will be preferred.

TABLE LXX.—AVEEAGE FLUIDITIES AND VAPOR PBESSUBES FOB CORRE-
SPONDING TEMPERATURES

Tem-
Toluene1
Benzene2
Hexamethylene3
Hexane4

pera-

ture,

Vapor

Vapor

Vapor

Vapor

degrees
9
pres-
<p
pres-
<f>
pres-
<p
pres-

C

sure

sure

sure

sure

o

110.8
25.3

252.3
45.4

10

131.5
45.2
84.7
47.0
281.8
75.0

20

154.1
75.6
101.7
76.9
312.4
120.0

30
192.3
32
178.0
120.2
121.3
121.3
344.8
185.4

40
214.6
60
203.1
183.6
141.8
181.6
378.8
276.7

50
238.6
94
228.8
271.4
164.8
269.2
414.9
400.9

60
262.7
140
256.1
390.1
188.7
385.0
452.7
566.2

70
287.8
203
284.9
547.4
214.5
540.8
494.6
787.0

80
314.5
291
313.8
751.9

90
342.8
405

100
371.4
560

110
400.0
751

1 Vapor pressure calculated from Kahlbaum, Zeitschr. /. physik. Chem.
26, 603 (1898). Fluidities from Bingham and Harrison, Zeitschr. f. physik.
Chem. 66, 1 (1909), and in the case of hexamethylene, hitherto unpublished
data of Bingham and van Klooster.
2 From Young, /. Chem. Soc. (London) 66, 486 (1889).
3 From Young and Fortney, J. Chem. Soc. (London) 75, 873 (1899).
4 From Thomas and Young, J. Chem. Soc. (London) 67, 1075 (1895).