Density of saturated vapour

The most frequently used calibration procedure is based on temperature dependence of pressure of saturated mercury vapour [19,39-41]. At 25°C this pressure is of 0.0018 mm Hg height it corresponds to the vapour density of 20 pg/1. To get in the measurement cell a mercury concentration of about 10 ng/1, the saturated vapour should be strongly diluted. Instead of dilution, a lower temperature can be used however, the density of saturated vapour of 10 ng/1 corresponds to the temperature of less than —40°C. Both dilution and temperature decrease can be realized easily in laboratory conditions but their incorporation into a miniaturized chemical sensor is rather complicated. An attempt to develop such a device is reported in Ref. [41]. An additional problem in application of these techniques in portable sensing devices with integrated calibration is the necessity to have a reservoir with mercury in the device it complicates recycling of these devices and does not correspond to modern trends in technology. 

In figure (9), the curves VC and LC show the plots of the densities of saturated vapours and those of liquid against the corresponding temperatures. The point C, where the two curves meet gives the critical temperature. This point is not sharp as the curve in this range is rather flat. 

The same apparatus was used for the determination of the densities of saturated vapour, in which case both liquid and vapour were present in the tube ( 4.VIII H). 

By using values for the densities of saturated vapour found by Schoop, Schumann found satisfactory agreement with Winkehnann s formula for the vapour pressures of aliphatic esters, whilst Duhring s formula gave very different specific factors. 

Schoop, with an apparatus similar to Herwig s, measured the densities of saturated vapours of benzene, methyl, ethyl, and propyl formates, methyl and ethyl acetates, and methyl propionate, and confirmed equation (2) up to 60°, beyond which the constant diminished for methyl acetate ... 

P6rot5 determined the densities of saturated vapours by exposing a vacuous globe to the vapour, closing it when full of vapour, and weighing after cooling. Bauer used Archimedes principle, weighing a float in the vapour. 

Young found from van der Waals s equation that the ratio of the actual density at the critical point to the theoretical density for the ideal gas should be (8/3)- /2=3 77 for all substances. The actual values are not far from this, except for alcohols and acetic acid, which have values of 4 to nearly 5. The density of saturated vapour is equal to the ideal gas density at the same corresponding temperature multiplied by a constant k ... 

Fairbum and Tate s method for density of saturated vapour, 325 falling drops, 14... 

Hagen-Poiseuille law, 72 Hagenbach coefficient, 74 correction, 73, 75 hanging drop, 183, 189 level viscometer, 80 Hare s apparatus, 12 Harkins s equation, 155 heat capacity of electrolyte solution, 225 content of electrolyte and non-electrolyte solutions, 225-6 content of vapour, 348 Heilborn s specific heat formula, 218 Henning s latent heat formula, 307 Herwig s method for density of saturated vapour, 325... 

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