A Practical Manual On Sea Water Distillation
With A Description Of The Necessary Machinery For The Process

228 SEA WATER DISTILLATION. t' Temperature of other surface. e = Thickness, or distance apart, of surfaces. C = Conductibility of the substance (i.e., the value of M for t — f). Then— M = e In his treatise, Péclet says that Biot, in 1816, verified this formula by experiment, and that later (1836) Despretz made further experiments confirming Biot. Péclet, how- ever, casts doubt on the foregoing experiments, saying they were obtained under circumstances rather too special to be practical; he, therefore, in 1841, made very exhaustive experiments dealing with substances (mostly bad conductors of heat), and the results (cpn- verted into English equivalents for convenience) will be found in “ Box on Heat.” With respect to the passage of heat through metals, Péclet gives the following ratio as the results of the earlier experiments of Biot and Despretz, but, for practical purposes, it will be found safer to go by the Table given on p. 96.* Gold (as standard),__________________1,000 Platinum,....................................981 Silver,......................................973 Copper,......................................898 Iron,........................................374 Zinc,........................................363 Tin,.........................................303 Lead,........................................179 Where silver is given as the standard.