M. Achille Cazin on Internal Work in Gases. 87 



Part I.- — Experimental Researches. 

 § T. Principle of the method. 



The gas is enclosed in two reservoirs at the same temperature, 

 connected by a large stopcock; one of them can communicate 

 with an open-air manometer. The stopcock being open, com- 

 munication with the manometer is first established; then the 

 stopcock is closed, communication with the manometer is cut off, 

 and by means of a pump a portion of the gas is made to pass from 

 one reservoir to the other. To make an experiment the stopcock 

 is opened ; the compressed gas begins to move, and communica- 

 tion is established with the manometer at a stated time from the 

 moment when the opening of the stopcock commenced. The 

 displacement of the level of the manometric liquid is followed, 

 and its successive positions are noted at stated periods. A curve 

 can thus be traced, of which the abscissae measure the periods, 

 and the ordinates the excesses, positive or negative, of the hy- 

 drostatic pressure of the liquid in motion over the final and sta- 

 tionary pressure of the liquid at rest. When certain conditions 

 are satisfied we generally obtain a curve ab cde (Plate I. fig. 1). 



The abscissa o a indicates the time which elapsed from the 

 opening of the stopcock to that of the manometer; the segment 

 of the curve ab c denotes that the variable pressure of the gas 

 was at first less than the final pressure p 1 ; the segment cde in- 

 dicates that this pressure afterwards became greater and then 

 gradually decreased to p'. A series of experiments are made by 

 changing the time o a, all other circumstances remaining the 

 same, which changes the position of the single points of the 

 curve; and by comparing the various curves belonging to the 

 same series, we deduce the succession of pressures which the gas 

 possessed during the motion in the reservoir which communi- 

 cated with the manometer. 



§ II. Description of the apparatus. 



The metal reservoirs A and B* (fig. 2), connected by a large 

 brass stopcock C, are fixed horizontally on a solid support ; they 

 have a double envelope, and the circulation of water ensures to 

 their sides a constant temperature; the gas flows through a 

 short and thick tube (length 28 centims., minimum diameter 4 

 centims.). On each side of the stopcock are tubes (D, E) pro- 

 vided with stopcocks and connectors in order to establish various 

 communications. The axis of the key of the large stopcock C 



* The reservoir A was of copper ; it had a capacity of 8'923 litres at 18°. 

 The reservoir B was of very strong zinc ; some iron hoops were soldered 

 to the interior; the capacity was 33*805 litres at 15° ; the connecting-pipe 

 contained 0140 litre. 



