296 THE EARL OF BERKELEY, MESSRS. E. G. J. HARTLEY AND C. V. BURTON : 
re-determination, the more so in that his air values seem in themselves not very 
satisfactory, and it is just the air values which are wanted in the majority of 
researches. The experimental error of our results is now reduced sufficiently to 
warrant the belief that in absolute measurements the chief difficulty will lie in the 
determination of the quantity of air passed, rather than in the amount of water 
vapour it carries. 
The research is divided into two parts. In Part I. are given the measurements of 
the compressibilities of the solutions; these were carried out with the aid of 
Dr. Burton, Part II. embodies the experiments on the vapour pressures of solutions 
of cane sugar and a-methyl glucoside at 0° C. and 30° C., also some determinations of 
the vapour pressures of dilute sulphuric acid. All the experiments, except a few 
dating later than January 22, 1916, were done in conjunction with Mr. Hartley. 
As both these gentlemen have left the laboratory and are not within reach, the 
other author should be held responsible for all mistakes in presentation of fact or 
theory. 
PART IA 
The Compressibilities. (Berkeley and Burton.) 
In a previous communication we have given the results of our measurements on the 
compressibilities of calcium ferrocyanide solutions. These results were not very 
satisfactory because the experiments had to be carried out as rapidly as possible, 
otherwise the prolonged strain on the outer glass tubef (through which the readings 
on the piezometer stem were taken) soon caused it to collapse. 
Neiv Apparatus .—To obviate this, a new apparatus, A, was designed in which the 
glass tube was replaced by a metal casting pierced for windows. With this 
apparatus some of the experiments here recorded were made ; but as the main 
features of A are embodied in yet another apparatus, B, the former will not be 
described. 
Fig. 1 shows B in elevation. The apparatus is divided into two main pieces, A 
and B, which are joined “ pressure tight ” by means of a dermatine ring as shown ; 
this method is similar to that described by us in ‘Phil. Mag.,’ vol. 32, 1916, p. 157. 
The upper part A (called the dome) is furnished with a pair of windows, C (the use 
of which will be described later), and is joined to the pressure system by a nut fitted 
with differential threads, by means of which the steel pressure tubing, E, can be forced 
home into its conical seating at D. The part B which is closed at the bottom by a 
nickel-steel plank (made “ pressure tight ” by dermatine), carries five pairs of windows, 
F, spaced at regular intervals for observing the level of the mercury in the stem of the 
* This part of the research was completed in 1911. 
t See ‘ Phil. Trans.,’ A, vol. 209, p. 192. 
