Relation to Pressure and Temperature, 481 



enlarged. The terms isometric, isopiestic, isothermal, isentrop- 

 ics, etc., are used in the present paper in the sense defined by 

 Gibbfl (1. c, p. 311). 



4:. Surveying the above researches as a whole, it appears at 

 the outset that more work has been spent on the compressi- 

 bility of water than the exceptional behavior of this substance 

 justifies at the present stage of the inquiry. In other words 

 the volume-pressure-temperature changes of the great majority 

 of liquids probably conform closely with a general thermo- 

 dynamic law, due respectively to Dupre and Levy, and to 

 Ramsay, Young and Fitzgerald. It is therefore first desirable 

 to find the full importance of this law experimentally, and then 

 to interpret the exceptional cases with reference to it. Again 

 it appears that researches in which long pressure ranges are 

 applied simultaneously with long temperature ranges, are 

 urgently called for. It is from such work that further eluci- 

 dation of this important subject is to be obtained. 



Among pressure experiments the late researches of Amagat 

 stand out by their originality and importance. One can not 

 but admire the experimental prowess which has enabled him to 

 penetrate legitimately into a region of pressures incomparably 

 high, without lowering his standard of accuracy. 



Apparatus. 



5. Force pump and ajipurtenances. — In making the experi- 

 ments detailed in the following pages I used a large Cailletet 

 force pump, of the form constructed both by Ducretet of Paris, 

 and by the Societe Genevoise. Its efficiency is 1000 atm. It is 

 made to be fed with water, but I found by using thin sperm 

 oil, it was possible to facilitate the operations, because there is 

 less clanger of rusting the fine polished steel parts of the ma- 

 chine. The pump consists of two parts : the pump proper and 

 the strong cylindrical trough into which the compression tubes 

 are to be screwed. The trough is cannon-shaped, its axis ver- 

 tical, and the open end uppermost. Pump and trough are 

 connected by strong phosphor-bronze tubing, and similar tubes 

 lead to the large Bourdon gauge by which the pressures are 

 measured. 



