pensating
transformation, thus constitutes an irreversible cycle, the outside
effects of which are that energy somewhere or other must be less capable
of transformation than it was before the change. We express this fact by
stating that an irreversible process essentially implies a loss of
availability. To measure this loss we make use of the laws of
thermodynamics, and in particular of Lord Kelvin's statement that "It is
impossible by means of inanimate material agency to derive mechanical
effect from any portion of matter by cooling it below the temperature of
the coldest of the surrounding objects."

+-------------------------------------------+------------+---------------------+--------------+
| Substances. | Temp. | K. | Author. |
+-------------------------------------------+------------+---------------------+--------------+
| Carbon dioxide and air | 0 deg.C.| 0.1423 cm^2/sec. | J. Loschmidt.|
| " " hydrogen | 0 deg.C.| 0.5558 " | " |
| " " oxygen | 0 deg.C.| 0.1409 " | " |
| " " carbon monoxide | 0 deg.C.| 0.1406 " | " |
| " " marsh gas (methane) | 0 deg.C.| 0.1586 " | " |
| " " nitrous oxide | 0 deg.C.| 0.0983 " | " |
| Hydrogen and oxygen | 0 deg.C.| 0.7214 " | " |
| " " carbon monoxide | 0 deg.C.| 0.6422 " | " |
| " " sulphur dioxide | 0 deg.C.| 0.4800 " | " |
| Oxygen and carbon monoxide | 0 deg.C.| 0.1802 " | " |
| Water and ammonia | 20 deg.C.| 1.250 " | G. Hufner. |
| " " | 5 deg.C.| 0.822 " | " |
| " common salt (density 1.0269) | | 0.355 cm^2/hour. | J. Graham. |
| " " " " |14.33 deg.C.| 1.020, 0.996, 0.972,| " |
| | | 0.932 cm^2/day. | F. Heimbrodt.|
| " zinc sulphate (0.312 gm/cm^3) | | 0.1162 " | W. Seitz.