Ramsay and Shields

We have so far succeeded in establishing connections between surface tension and a number of physical properties, but have not yet found a relation between the former and any chemical constant. A very simple and general relation of this kind was first pointed out by the Hungarian physicist Eotvos and confirmed experimentally, for a large number of liquids, by Ramsay and Shields. If M is the molecular weight of a liquid and p its density, then... 

N20 (liq.), N20(c). The heats of vaporization and fusion are evaluated from the data of Eucken and Donath,1 Cailletet and Mathias,1 Young,2 Burrell and Robertson,3 Bergstrom,2-3 Regnault,7 Cardoso and Ami,1 Grunmach,1 Villard,1-3-9 Kuenen,1 Ramsay and Shield,1 Pictet,1 Hunter,1 Dewar,2 Faraday,1-3 Britton,1 Cailletet and Colardeau,1 Marshall and Ramsay,1 Mathias,1-2 and Mills.1... 

The surface tension of most liquids decreases with increasing temperature in a nearly linear fashion (some metal melts being exceptional in this respect) and becomes very small in the region of the critical temperature, when the intermolecular cohesive forces approach zero. A number of empirical equations have been suggested which relate surface tension and temperature, one of the most satisfactory being that of Ramsay and Shields ... 

These abnormally low values were supposed to be due to association of the molecules of the liquid, M being higher than calculated from the formula. Assuming that the whole change in the number of molecules in the surface is due to simple association of molecules of molecular weight M to molecules of weight Mv Ramsay and Shields calculated the degree of association thus... 

The accuracy of (5) is within the limits of experimental error for many liquids. As the linear relation does not usually hold near the critical temperature, (6) is less accurate, though it is preferable theoretically as containing one less arbitrary constant. Refinements of the linear equation have usually been made along one of two lines the first is to follow Eotvos s plan of introducing the twro-thirds power of the molecular volume, as in equation (1) of Ramsay and Shields, or Katayama s modification2... 

Engler and Wohler, Zeitsch. anorg. Ghem., 1902, 29, 1 Mond, Ramsay, and Shields, loc. cit... 

Ramsay and Shields, Phil. Trans., 1896, 186, 657. See also Lucas, Zeitsch. Elektro-... 

The results obtained by Ramsay and Shields 4 in their classical research, in which water was in contact with its vapour and the walls of the capillary tube only, are given on p. 273. 

The values obtained for x at temperatures ranging from 0 to 120° C., as given by Ramsay and Shields, are detailed in the fifth column of the table on p. 299. It will be observed that at low temperatures the water appears to approximate to the tetrahydrol (H20)4 molecule. As the temperature rises, the mean molecular weight falls owing to increasing depolymerisation. 

It has already been mentioned, however, that the values for the surface tension as determined by Ramsay and Shields are more than 2 per cent, too low in consequence of a systematic error throughout the series. Assuming the above relationship between a and M to be strictly true, it follows that the degree of association of the water is lower than that calculated. 

Temperature, °0. Specific Cohesion, a2. Vapour Pressure, mm. X1 (Dutoit and Mojoiu). (Ramsay and Shields). (Ramsay and Rose Innes). 

Since surface tension vanishes roughly 6 C above the critical temperature rather than at the critical temperature, Ramsay and Shields proposed the following equation for the temperature-dependence of surface tension ... 

Ramsay and Shields <5 found experimentally that a small correction is necessary, so that (2) becomes ... 

Hunten and Maass found that the Ramsay and Shields constant increased rapidly in homologous series of fatty acids with Ncarbon atoms, fc=(2 12/3-95)... 

Ramsay and Shields calculated the degree of association as foUows ... 

For fused metals anomalous results for the association factor x below 1 are found, whilst fused salts give peculiar results, sometimes indicating an association factor of 10. (In such cases, equation (1) must be used, since the critical temperatures are unknown and must be very high.) These are, however, extreme cases of application. The abnormalities in general seem to be connected with the value of the critical temperature, At present, it is fairly generally agreed that, whilst low values of k for liquids about room temperature point to association, the calculation of an association factor x by Ramsay and Shields s method is unjustified. ... 

Richards and Coombs, J,A,C,S., 1915,37, 1656 Richards and Carver, ibid, 1921, 43, 827 Richards, Speyers, and Carver, ibid, 1924, 46, 1196 Hunten and Maass, ibid, 1929, 51, 153 Harkins and Jordan, ibid, 1930,52, 1751 Neros and Eversoll, J, Phys, Chem, 1941,45,388. The apparatus used by Ramsay and Shields (see below) would be affected by this error a correction for one tube inside another (as used by them) is given by Verschaflfelt, Bull, Acad, Roy, Belg, 1921, 574. For an improved Richards apparatus, see Harkins, in Weissberger, Physical Methods of Organic Chemistry, New York, 1945,1,160. Z,phys, Chem, 1912, 79, 700. 

Jones and Ray used a modification (capillarimeter) of Ramsay and Shields s apparatus in.Avhich the different liquids are brought to the same height in the enclosed capillary by adding them to the outer vessel, and the weights of the liquids added are found. The method is comparative. The rise of mercury in (opaque) metal tubes can be investigated by X-rays. ... 

In Ramsay and Shields s calculations, the simple formula (1), 13.VIII G, (T=jgQfir, where is the density of the liquid,... 

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