Density variation with rank

The density of coal shows a notable variation with rank for carbon content (Figure 6.1) and, in addition, the methanol density is generally higher than the helium density because of the contraction of adsorbed helium in the coal pores as well as by virtue of interactions between the coal and the methanol, which results in a combined volume that is notably less than the sum of the separate volumes. Similar behavior has been observed for the water density of coals having 80 to 84% w/w carbon. 

Figure 2.30. The v iation of total porosity Figure 2.31. The variation of helium density (vol%) with coal rank. (gcm ) with coal rank (Toda, 1972).

Figure 2.31 shows the variation of helium density (gcm ) with coal rank for all coals. Helium, as a gas, has the advantage of being able to penetrate into porosities and yet not to be adsorbed (This is not strictly true and adsorption of helium can be detected but this effect does not radically alter the major conclusions). 

To compare between days and locations I standardised visitation rates for each species by calculating visits to each odour type as a proportion of mean visits to the blank stations by that species, on that night, and at that location. By making the data proportional I removed effects of differing population size and density, as well as variation between nights, for example in moon phase. These data were checked for normality and symmetry, and subsequently analysed with a two-tailed Wilcoxon signed ranks test (Zar 1999) to determine whether visitation rate differed from a value of one (indicating no difference between visitation rate to an odour source... 

A property for which generally good experimental data are available is molar refraction (MR), a composite of refractive index, density, and molecular weight. Because of its relation to polarizability, it has been used in many QSAR relations as a regression variable. It is observed that the relation between MR and skeletal variation is very different from the relation between heat of atomization and structure. The heat of atomization for a set of alkane isomers is generally ranked rather well by the x index the most stable isomer in a set generally has the smallest value of the chi-one index. Such is not the case with MR the MR values in an isomer set follow a much different pattern with x- We expect, then, a rather different QSAR for MR than for AH.,. For alkanes the following QSAR is obtained ... 

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