of Air wider Volume and under Pressure. 331 



was this excess which prevented the liquor from rising to the 

 same height as before. 



With the view of making similar experiments, which should 

 be in a great measure free from such objections, I had an appa- 

 ratus fitted up on purpose. It consists of a large flask, made of 

 strong tinned iron, and capable of containing 2300 cubic inches 

 of air. The neck is of brass, about two inches wide ; and into 

 this was fitted by grinding a brass stopper, hollow and open in- 

 ward. At equal distances from each other^ four apertures were 

 cut through the sides of the neck and of the stopper. Each is 

 1.2 inch long and 0.6 broad ; so that these together can form a 

 communication between the atmosphere and included air, equal 

 to 2.88 square inches, or the opening of fourteen half inch stop- 

 cocks, and which communication can be both opened and shut 

 by simply turning the stopper one-fourth round,-^ — an operation 

 which requires but a very small moment of time. 



Near the neck, a tube branches out, and joins a vertical glass 

 tube, which, terminating in some light liquid, forms the same 

 sort of gauge as in the apparatus first alluded to ; and, on the 

 opposite side^ is an aperture for attaching a pump or condenser 

 to change the density of the included air. The air-vessel is in- 

 closed in another, both for the purpose of keeping the tempera- 

 ture steady, and also for applying a bath to maintain any tem- 

 perature required. But, during tempestuous weather, or when 

 the barometer is very unsteady, no experiments can be made 

 with such apparatus. 



As a preliminary step in the use of this instrument, it is ne- 

 cessary to ascertain at what rate we should turn the stopper, in 

 order that the included air, when its pressure has been previous- 

 ly changed from that of the atmosphere by about 0.4 inch of 

 mercury, may have a sufficient opportunity of regaining the ex- 

 ternal pressure. To determine this, the following method was 

 employed : Having injected air till the increase of pressure, 

 when the temperature had settled, was indicated by a depressed 

 column of water of about six inches, I turned the stopper one- 

 fourth round, by which it was both opened and shut. During 

 this operation, I noted how far the previously depressed water 

 in the gauge tube started above the common level. The same 

 operation was repeated, with the difference of only turning the 



