Thermodynamic Properties of Air. 9 



The calorimeter K — a vessel of thin sheet silver, capacity 

 about 250 cub. centims., weight 98*310 grammes — rests on 

 three pointed glass feet inside a double-walled brass enclosure 

 Z, protected on the outside by sheets of paper and cotton- 

 wool ; the space between the walls is filled with water. 

 Through several openings in the double sheet-brass cover of 

 the enclosure there are introduced into the calorimeter : — 

 (1) the cooler S, (2) the stirrer M, the oscillations of which 

 are maintained by a heavy pendulum (not shown), (3) the 

 thermometer T. 



The thermometer T, an excellent instrument furnished by 

 G. Fontaine of Paris, was divided in 0*02 degr. (from — o, 5 

 to +0°-6 and + ll°-5 to +22° 3). It has been standardized 

 with reference to tbe hydrogen scale by the Central Office of 

 Weights and Measures at Vienna. The corrections proved 

 so insignificant that it was possible to omit them altogether. 

 Weight of glass and mercury was determined by the maker. 

 h represents a small electromagnetic hammer, destined to 

 shake the thermometer T, in order to prevent any lagging of 

 mercury, t and t' are two auxiliary thermometers by means 

 of which the temperature of the stem of the principal ther- 

 mometer was determined in order to obtain the well-known 

 thermometric correction. 



The heater was constructed as follows : — A copper tube P, 

 one metre in length, internal diameter =2 millim., external 

 diameter =4 millim., is coiled round a vertical brass tube 

 D F, fixed along the axis of the heater. The outer end of the 

 copper tube is joined by means of a thick-walled indiarubber 

 tube with a T-shaped piece. One of its ends P' is connected 

 with the flasks filled with compressed air, the other N with an 

 open mercury manometer, which serves to control the velocity 

 and steadiness of the current of air. The inner end of the 

 copper spiral is connected by solder with the brass tube D F, 

 near its lower end, where a small hole (u, fig. 2a) is provided, 

 through which the air cooled in the spiral passes into the 

 brass tube, and thence through the connecting piece C into 

 the cooler S. The connexion consists of a thin-walled glass 

 tube C, some 25 millims. in total length, its upper end being 

 cemented by means of isinglass into the brass tube D F, the 

 lower end into the cooler S by sealing-wax. The glass tube 

 serves only to provide an air-tight connexion and to protect 

 against external heat the inner tube s, which is the real 

 delivering tube of the gas. The last-mentioned tube s is made 

 of very thin highly-polished sheet silver ; it is soldered to 



