Improved Eudiometrical Apparatus, by Dr. Hare. 47 
After the apparatus has, by these means, been purged of 
atmospheric air, the cocks, C and F, being open, suppose the 
rod drawn out 300 degrees. If the gaseous mixture in the 
bell consist of two volumes of air and one of hydrogen, of 
the 300 measures drawn in by the rod, 100 measures will be 
hydrogen, and 200 measures will be air. Under these cir- 
cumstances the cock, F, must be closed. In consequence of 
the hydrostatic pressure to which the gas will have been 
subjected in the bell, its density within the receiver will be 
greater than without. Hence the pressure of the screw, B, 
on the spring, L, must be relaxed until the gage indicates 
that the gas within the receiver has, by the escape of a por- 
tion of it, become, with respect to pressure, in equilibrio with 
the atmosphere. The cock, B, communicating with the 
gage, is then closed, the pressure on the spring is restored, 
pa By restoring the communication with the gage, and 
duly removing the rod, the compensation may be rendered 
he number of degrees which th . 
the residual gas will be expelled, and if there be no error in 
¢flecting the expulsion, the rod will just enter to the hilt. 
