330 Mr. J. Joly on a Method of 



4J millim. wide, and 1 millim. in thickness. The vessel must 

 be quite staunch. Its internal volume is just 160 cub. centim. 

 It is closed by a small screw- valve, having a side tubulure for 

 attachment to the various apparatus. The valve-spindle of 

 steel works through a small stuffing-box to prevent the escape 

 of gas along the shaft of the spindle when the vessel is being 

 filled or emptied. 



This vessel is tested hydraulically to 10001b. in the square 

 inch. It may be safely filled to pressures of 20 or 25 atmo- 

 spheres. I am daily using such vessels in the steam calori- 

 meter in determining the specific heats of gases ; here they 

 are raised to the temperature of 100° C, bringing the pressure 

 to near 30 atmospheres in many cases. For the purpose of 

 compressing the gas into this vessel I use a pump of special 

 construction, a description of which I hope shortly to publish. 

 But, obviously, any compression-pump which will deliver the 

 gas without contamination of oil or moisture will answer. 



A counterpoising sphere of the same bulk and weight 

 approximately is required. Against this, after the required 

 quantity of gas has been inserted in the weighing-sphere, 

 the latter is equilibrated. This operation is readily per- 

 formed in an ordinary chemical balance to an accuracy of 

 one tenth or one twentieth of a milligram. The weight of a 

 copper vessel of the strength described will be from 80 to 90 

 grammes. It will be seen later that one sufficiently strong to 

 hold 2 litres safely need not exceed some 40 grammes in 

 weight. 



The vessel in which the volume is determined is next to 

 be considered. It is lettered g in the diagram, wdiere it is 

 shown connected with the weighing-sphere, the latter screwed 

 to the steel connexion b provided for it, and through the fine 

 bore (1 millim.) of which it delivers its contents into g. The 

 volumenometer is of glass, cylindrical, closed at each end by 

 ground stoppers with tubulures attached. The upper tubu- 

 lure is of fine bore, hardly 1 millim., the lower tubulure of 

 some 3 or 4 millim. bore. The volumenometer is surrounded 

 by a copper jacket, having two large openings cut in its 

 cover for the admission of broken ice or water, and also a 

 tubulure for admitting a thermometer. A fine mark is etched 

 on the lower tubulure at /, and this tubulure is continued by 

 attachment to a smaller vessel c, as shown. This again is 

 connected by a rubber-tube connexion with the vessel d, which 

 can be raised or lowered, as will be understood from the 

 diagram. The volume of the volumenometer is best deter- 

 mined with water. If water is subsequently to be used in it 

 the procedure is as follows: — 



