152 Mr. J. T. Bottomley on a Practical 



fall-tubes in a Sprengel pump, t and t' 

 cocks 



t and t are two stop- 

 t being a three-way stopcock, connecting together the 

 Fig. 2. 



volume-gauge, the manometric gauge, and the pressure-pump; 

 and t' is a stopcock used for adjusting the quantity of liquid 

 in the volume-gauge. 



The object of the two cylindrical reservoirs b and V in the 

 volume -gauge is to give space into which the air in the bulb 

 a may expand during heating, or in which a supply of the air 

 may be kept during the cooling of the thermometer. The 

 tube d is very small in capacity in comparison with the bulb ; 

 and were it not for these reservoirs, a very small change in 

 temperature would cause the air to be driven out round the 

 bend of the U, or the liquid in the bend to be drawn over into 

 the bulb, unless the observer were incessantly on the watch to 

 prevent this occurring by regulating the pressure. 



The U of the volume-gauge is filled so full of liquid that 

 the equilibrium reading is taken at the points pp of the tubes 

 d and d'; and both in the selection of the tubes c and d, and 

 in the glass-blowing at the junction, as well as in the adjusting 

 of the quantity of liquid in the bend, the endeavour is made 

 to keep the volume of the air-space between the bulb and the 

 point p as small as possible, consideration being given to the 



