406 MR. J. H. BEINKWORTH ON THE SPECIFIC HEAT OF STEAM AT 



lessened, and in a few seconds equilibrium is attained ; the current of steam keeping 

 its own pressure constant. This pressure is measured on a manometer connected with 

 the tube, M. Perfection in regulation is not obtained until sufficient water has con- 

 densed in the limb, S, to fill the length of tube between the top of the mercury and 

 the exit, E, but to hasten this condition the tap, J, may be opened, thus allowing 

 water which has condensed in the bulb, F (which is also connected to the tube, M) to 

 run into the limb, S, until the latter is filled to the requisite height. The pressure of 

 the steam can be altered either by varying the amount of mercury in the regulator, 

 or by raising or lowering the end of the tube, A. At the end of every experiment 

 the main gas supply was cut off and the tap, H, closed, so that when the regulator 

 was put into action at the commencement of the next experiment, the limb, S, con- 

 tained sufficient water to ensure perfect regulation at once. It is necessary for the 

 gas supply to be constant, since variations in the pressure in the gas main produce 

 corresponding variations in the quantity of steam generated. Such effects were not 

 noticeable on the thermometric readings of the " cold temperature," but they were 

 quite evident when the heating current was on. Sudden and violent fluctuations 

 were prevented by passing the gas into the bell of a small gas-holder before it entered 

 the regulator. The accuracy of these experiments depends chiefly on the constancy 

 with which the pressure can be maintained, and the wonderful steadiness in the 

 temperature of the steam is exemplified in the extended tables of observations which 

 are given. 



From these it will be seen that the " cold temperature," observed after an interval 

 of about an hour, agrees to 0'03 cm. of bridge-wire or to about one two-hundredth of 

 a degree Centigrade, with that determined before the electrical energy was supplied. 



The Calonmetric Arrangements (fig. 7). 



The calorimeter proper consisted of a glass tube, Y, about 50 cm. long, in which 

 the heating coil, 0, and the thermometer sheath, N, were fixed. This tube was 

 jacketed by another glass tube, S, which enclosed the length occupied by the heating 

 coil and thermometer. In the following experiments three different types of calori- 

 meter were used, each of which will be described later in connection with the results 

 obtained. 



The calorimeter flow-tube and its surrounding glass sheath were carried on a split 

 rubber cork wound with omega tape and fixed, making a steam-tight joint, into a 

 space enclosed by a double-walled brass jacket, 45 cm. long and 5 cm. internal 

 diameter. From the lower part of this jacket there was a double-walled side-tube 

 60 cm. kmg, packed tightly with gauze discs, through which the steam had to pass 

 before it reached the calorimeter proper. The whole external jacket hence consists of 

 two L-shaped vessels, one inside the other, the space between the double walls being 

 continuous. 



