the critical volume of ether was approximately such at about the absolute boiling point, but the compressibility of the liquid is so great that the slightest change of pressure or temperature has a considerable effect on the volume. But the investigations of the above savants gave another indirect demonstration of the truth of van der Waals' equation. They also found for ether that the isochords, or the lines of equal volumes (if both _t_ and _p_ vary), are generally straight lines. Thus the volume of 10 c.c. for 1 gram of ether corresponds with pressures (expressed in metres of mercury) equal to 0·135_t_-3·3 (for example, at 180° the pressure = 21 metres, and at 280° it = 34·5 metres). The rectilinear form of the isochord (when _v_ = _a_ constant quantity) is a direct result of van der Waals' formula. When, in 1883, I demonstrated that the specific gravity of liquids decreases in proportion to the rise of temperature [S_{_t_} = S_{_0_}-K_t_ or S_{_t_} = S_{_0_}(1-K_t_)], or that the volumes increase in inverse proportion to the binomial 1-K_t_, that is, V_{_t_} = V_{_0_}(1-K_t_)^{-1}, where K is the modulus of expansion, which varies with the nature of the liquid, then, in general, not only does a connection arise between gases and liquids with respect to a change of volume, but also it would appear possible, by applying van der Waals' formula, to judge, from the phenomena of the expansion of liquids, as to their transition into vapour, and to connect together all the principal properties of liquids, which up to this time had not been considered to be in direct dependence. Thus Thorpe and Rücker found that 2(_tc_) + 273 = 1/K, where K is the modulus of expansion in the above-mentioned formula. For example, the expansion of ether is expressed with sufficient accuracy from 0° to 100° by the equation S_{_t_} = 0·736/(1-0·00154_t_), or V_{_t_} = 1/(1-0·00154_t_), where 0·00154 is the modulus of expansion, and therefore (_tc_) = 188°, or by direct observation 193°. For silicon tetrachloride, SiCl_{4}, the modulus equals 0·00136, from whence (_tc_) = 231°, and by experiment 230°. On the other hand, D. P. Konovaloff, admitting that the external pressure _p_ in liquids is insignificant when compared with the internal (_a_ in van der Waals' formula), and that the work in the expansion of liquids is proportional to their temperature (as in gases), directly deduced, from van der Waals' formula, the above-mentioned formula for the expansion of liquids, V_{t} = 1/(1-K_t_), and also the magnitude of the latent heat of evaporation, cohesion, and compressibility under pressure. In this way van der Waals' formula embraces the gaseous, critical,