106 Prof. Oersted on the Compression of Gases. 



pansion are in proportion to the quantities of air which had 

 been put into it. If the reservoir had not been extended after 

 101*2 grammes of air had been forced into it, the density of 

 this air would have equalled 113*5 of the atmosphere; but 

 taking into consideration the expansion of the reservoir, it only 

 amounted to 110*5. 



The third figure shows the manner in which we carried on 

 our experiments on the expansive power of the air compressed 

 in such a reservoir. AB represents such a reservoir, i. e. the 

 but-end of an air-gun ; CD is a board with a perpendicular 

 lath CE; EH is a piece of iron which in its upper part re- 

 ceives the axis, round which turns the lever FG, which again 

 is balanced by a counterpoise, F. This lever has a tooth I, 

 pressing on the valve M, of the but-end MB fastened under- 

 neath it. A slide N with a scale L appended to it, serves to 

 determine the power necessary for opening the valve. This 

 valve being closed by a spring, we began by investigating the 

 power necessary to open the valve when the density of the 

 inclosed air corresponded with that of the atmosphere. After 

 this the reservoir was loaded as much as possible ; and after 

 having measured the resistance occasioned by the inclosed air 

 against the valve, we gradually emptied the reservoir, con- 

 stantly weighing the remaining air by means of scales and 

 weights, and determining its expansive power by means of the 

 apparatus fig. 3. Experiments of this kind, however, are not 

 susceptible of great accuracy, since the valve does not always 

 close uniformly. If the valve is lined with leather, for the 

 purpose of making it close more tightly, that inequality is very 

 great ; for which reason we began a series of experiments with 

 a steel valve closely ground-in, which, however, prevented us 

 from obtaining equally strong charges. 



The following tables give the result of both experiments, 

 the first column of which shows the air forced into the reser- 

 voir ; the second, its density ; the third, the force requisite for 

 opening the valve, — that which was necessary before loading 

 being deducted ; and the fourth, the pressure of the atmo- 

 sphere, being the product of the magnitude of this power di- 

 vided by the degrees of densitjr. 



Table 



