AND RATIO OK THEIR ATOMIC WEIGHTS. 87 



7. DENSITY OF ELEOTltULYTIC GAS. CLOSING THE Gl.OIiES DlIUINCi TIIK ANALYSIS 



OF THE GAS. 



It was necessaiy to close the globes in such a way as to prevent the inti'oduc- 

 tion of air, not only during the measurement of pressure, hut also dui'lii"- the with- 

 drawal of the gas used for analysis. During the measurement of ])i'essure, the 

 voltameter was left connected as during the filling. Both stopcocks were shut, and 

 the pressure was the same in the globes and the voltameter. Leakao'e, theiefore, 

 could not take place. 



In order to prevent leakage for a day or two, and against an inequality of 

 pressure, the stopcock g, Fig. 29, could not be trusted. Of coui'se it was im[)ossil)le 

 to fuse the tube. I therefore bent the tube by which the gas was admitted, as 

 shown at r q. At the bottom of the short U tube was a branch through which 

 mercury could be admitted to fill the bend. A mark at s defined the volume whose 

 capacity was determined in the calibration. To this point the mercuiy was brought 

 during the measurement of pressure. When the voltameter was to be discon- 

 nected, the mercury was made to fill the bend. If now slight leakage should 

 take place through the key of the stopcock, it could be detected ])y the change of 

 level of the mercuiy in time to admit of i-emedy l)efore the gas in the apparatus 

 was contaminated. 



8. DENSITY OF ELECTROLYTIC GAS. CLOSING THE VOLTAMETER. 



The stopcock of the voltameter was closed, or the fusible metal plug was I'e- 

 placed, and the apparatus was wiped and again weighed, as before. The \'oluraes 

 on the two sides were made equal, and the weighings were by reversal. 



9. — DENSITY OF ELECTROLYTIC GAS. PREPARING THE VOLTAMETER FOR A 



FOLLOWING EXPERIMENT. 



The weight of the gas delivered l)y the voltameter was about twenty-three 

 gi'ammes in each experiment. Instead of adding successive increments of tweutj'- 

 three grammes, to make up this loss of weight, the countei'poise was made lighter 

 by this amount. The counterpoise consisted of a number of the tubes of the same 

 glass as the voltameter, closed by fusion, one of which was loaded with mei'cury. 

 A duplicate of this loaded tube was adjusted by removing mercury to the amount 

 indicated by the weighing just made, so that when the weighing of the voltameter 

 after an experiment was finished, the duplicate counterpoise was ready, with its 

 weight about the same as that of the voltameter. A current was passed through 

 it for a few minutes and its stopcock was opened to secure that the pressure in it 

 should be that of the atmosphere, and the indications of the gauge were verified 



