PHYSICAL PROPERTIES OF WATER, ETC. 



15 



This formula represents a parabola which is everywhere convex upwards, and thus 

 cannot possibly be consistent with the existence of a minimum compressibility. 

 Instead of representing the results of new experiments, it is based on data extracted 

 from the old and very dubious results of Grassi (two data being wrongly quoted), 

 Descamps, and Wertheim, which differ in the wildest way from one another. What 

 method of calculation has been employed upon this chaotic group we are not told. 

 The result is a smug little table (D. IX.), in which no single entry can be looked upon 

 as trustworthy! Plate II. fig. 1, shows some of the materials, as well as the final 

 extract or quintessence derived from them. 



III. The Piezometers — Reckoxixg of Log. Factors— Compressibility of 



Mercury. 



V 



J 



The annexed sketch shows the form of piezometer employed. Six of these instru- 

 ments, three filled with fresh w r ater and three with sea-water, were simultaneously 

 exposed to pressure. The upper end of the bulb at B was drawn out 

 into a very fine tube, so that the instruments could be opened and refilled 

 several times without appreciable change of internal volume. They were 

 contained in a tall copper vessel which was let down into the pressure 

 cylinder, and which kept them (after removal from it) surrounded by 

 a large quantity of the press water till they could be taken out and 

 measured one by one ; each, after measurement, being at once replaced 

 in the vessel. Large supplies of water were kept in tin vessels close to 

 the pressure apparatus ; and the temperatures of the contents of all were 

 observed from time to time with a Kew Standard. 



The stems, A C, of the piezometers were usually from 30 to 40 cm. 

 iu length, and the volumes of the cylindrical bulbs, CB, were each 

 (roughly) adjusted to the bore of the stem, so that the whole displace- 

 ment of the indices in the various vessels should lie nearly the same for 

 the same pressure. At A, on each stem, below the working portion, the 

 special mark of the instrument was made in dots of black enamel (e.g. 

 .:, .., ;, &c), so that it could be instantly recognised, and affixed 

 to the record of the index in the laboratory book. Above this enamel 

 mark a short millimetre scale was etched on the glass for the purpose of 

 recording the volume of the water contents at each temperature before 

 pressure was applied. The factor by which the displacement of the 

 index has to be multiplied, in order to find the whole compression, varies 

 (slightly) with the initial bulk of the water-contents. This, in its turn, depends on 

 the temperature at which the experiment is made. Practically, it was found that no 



