II. RESEARCH. 621 



tube, in which the gases are measured under determined conditions of tem- 

 perature and moisture, 2. The experimental tube. The upper part of the 

 iron upright is furnished with a copper carrier, to which is fixed a steel stop- 

 cock, which is connected with another similar one by means of a collar. 

 The stop-cock fixed to the carrier is cemented to the measuring tube which 

 dips into the cylinder ; the second steel stop-cock is cemented to the ex- 

 perimental tube, and dips into the vessel of mercury. It can be seen by this 

 arrangement that it is easy to connect or disconnect the experimental tube and 

 the measuring tube, to make the gas pass from the experimental tube into 

 the measuring tube, or to make the mercury run into either of the two tubes 

 of the manometer apparatus, as is explained by M. llegnault, vol. 4, p. 73, 

 '' Cours de Chemie Elementaire." 



2456m. Hegnault's Apparatus for measuring the 

 Coefficients of expansion of Gas. 



Golaz, 22 Rue dcs Fosses, St. Jacques, Paris. 



This apparatus consists of two distinct parts, a boiler and a manometer 

 The boiler is a brass vessel in which either water or ice is placed, it is closed 

 by a cover provided with a tube by which the vapour may escape, and is 

 supported by a cast-iron stand on which it can be raised or lowered ; it is 

 also capable of motion in a horizontal groove, which allows of its being 

 advanced or withdrawn. 



A large alcohol lamp, which is also capable of being raised or lowered, 

 is used for heating the water. 



The manometer consists of a mahogany board fixed to an iron stand sup- 

 porting an iron framework furnished with two vertical tubes connected by a 

 three-way cock ; by this means communication can be established between 

 the two tubes or with the outside air. Thus the mercury can be made either 

 to pass from one tube into the other, or to flow away from either into the 

 outside air. Inf.o one of the tubes is cemented a glass tube with millimetre 

 graduations, and ending at its upper part in a capillary glass tube ; the second 

 tube is graduated like the first, and terminates in an opening, which con- 

 stitutes an open manometer. The capillary ending of the first tube is closed 

 by a steel three-way cock. 



A glass globe of about three-quarter litre capacity is fixed in the heater, 

 and iuto it is introduced the gas to be investigated. The globe is attached to 

 the stop-cock of the manometer by means of a copper capillary tube, the 

 flexibility of which renders the adjustment of the apparatus easy. In the 

 first apparatus of this description constructed the tube was of glass and 

 cemented to the globe, but this method was found to render the formation of 

 a proper joint very difficult. 



The details of the experiments made with the apparatus are to be found 

 in the " Memoires de FAcademie des Sciences," tome 21, page 96, and 

 plate 1, fig. 7." 



For this second method the same boiler find globe are employed. The 

 manometer alone is different. It is composed of two tubes, the first having 

 a large diameter for the greater part of its length, and ending in a capillary 

 tube attached to a steel stop-cock, the second tube is open at its upper end. 

 This part of the apparatus is enclosed in a case of strong canvas, provided 

 with a glass side, thus permitting the manometer to be kept at a constant 

 temperature, and the progress the experiment at the same time to be 

 watched. 



The capillary tube of the globe in the boiler is connected with the steel 

 stop-cock of this apparatus. 



An air-pump or pneumatic apparatus is put into communication with the 



