21 



tightly screwed against the caoutchouc plate in the small stand, 

 and the whole placed in the large tube containing some mercury, 

 and filled up with water. The pressures within and without the 

 tube are equalised by slightly unscrewing the tube from the 

 caoutchouc plate, and it is again closed. The iron lid is fastened 

 down and the apparatus vigorously agitated. The tube is 

 again released to equalize the pressure, screwed down again and 

 the apparatus agitated ; this operation being repeated until r.o 

 further diminution of the volume of the gas is perceptible. The 

 volume of the water is determined by reading off its upper and 

 lower level in the absorption tube. The diminution of the 

 original volume of the gas corrected for the pressure it is under 

 in the absorptiometer gives the amount absorbed by the water 

 at the temperature given by the thermometer. 



105. Bunsen's thermostat. 



E. 92. 1888. Made by 0. Desaga. 



Is an air bath of tolerably large dimensions, in which almost 

 perfectly constant temperatures can be kept up for any desired 

 length of time. 



It consists of a cylinder of sheet copper closed at the lower 

 end ; its section is an ellipse. From this cylinder at 11 

 places, equally distant from each other, project thick copper 

 wires which are riveted and brazed into the copper cylinder. 

 The wires pass through the lamp chimneys in such a manner 

 that they lie at right angles to the vertical axes of the cones of 

 the non-luminous flames, and are placed at the point where the 

 temperature is highest and most uniform. By this arrangement 

 it is seen that the temperature of the interior of the copper 

 vessel is rendered very nearly independent of the height of the 

 flame, and is almost entirely regulated by the distance of the 

 lamps from the cylinder. To avoid irregularities in the dis- 

 tribution of heat in this way, a somewhat smaller copper vessel, 

 also closed below, is firmly connected to the outer one, in such a 

 manner that a thin layer of air separates the one from the other ; 

 this effectually prevents irregularities from radiation from the 

 outer vessel. The upper ends of both copper vessels can be 

 closed with covers pierced with three corresponding holes ; 

 through two of which project the points of the glass vessels 

 which are being heated, and through the third a thermometer. 

 The whole apparatus is protected from draughts, and the gas 

 supply is governed by a regulator. The flames can be arranged 

 in three different positions equidistant from the copper vessel, 

 and these may be recognised by notches on the conducting rod, 

 and correspond to certain temperatures. After having taken full 

 precautions, the temperature of the air bath during one hour 

 will not vary more than one degree. 



