426 
PROFESSOR J. W. MALLET OX THE ATOMIC WEIGHT OF GOLD. 
metal going farther along the tube towards The stopcock c was closed, with the 
tube on which it was situated completely full of mercury, and leaving surplus mercury 
in the funnel a. In filling h and its connected tubes care was taken to leave no visible 
o 
bubbles of air. Pure water mixed with one-twelfth its weight of pure sulphuric acid 
was boiled for some time in a small flask to expel all dissolved air, keeping up the 
volume by additions from time to time of water kept boiling in a second flask ; the 
lower turned-up end of the tube h was then immersed in the dilute acid, and the lower 
end of g in a cup of mercury ; on opening the stopcocks e and d mercury ran out from 
g, and the dilute acid came in through h, filling about half full the cylinder 6. Closing 
d and e, opening c, and keeping up a supply of mercury in the funnel a,f was now 
turned so as to force out through the base of this stopcock the little mercury in the 
tube behind it, and fill this tube with the acidulated water. Then f was turned so as to 
allow of this acidulated water being forced on to the bend i and into the two little volta¬ 
meter tubes k and k, filling these about one-third full. While these tubes were being 
thus filled the extremities of the deliveiy tubes m and m were in communication with 
a Sprengel pump, so that they were very nearly exhausted of air. The stopcock f 
having been closed, e was opened, and by suitable tilting of the apparatus, and running 
in of mercury from the funnel a, nearly all of the acidulated water from y backwards 
was expelled through the tube h. A repetition of the procedure by which the cylinder 
h had been partially filled with acidulated water now served to partially fill it with 
well-boiled and still hot distilled water to which no acid had been added. The two 
delivery tubes m and m were severally detached from the Sprengel pump, after 
allowing (by a special separate arrangement of tubes with stopcocks) hydrogen to 
enter one of the two and oxygen the other, and when thus filled the ends of these 
two tubes were dipped under mercury, and the two platinum wires, I and I, sealed 
into the voltameter tubes were connected by the little rings on their outer ends with 
the terminals of the galvanic cells whence the electric current was to be derived, 
taking care, of course, to connect to the negative pole the wire of the tube already 
filled in its upper part with hydrogen, and to the positive pole the wire of the oxygen 
tube. Viewed from the front, the two voltameter and delivery tubes presented the 
aj)pearance shown in fig. G. The little voltameter tubes k and k had an external 
diameter of about 12 mm. and a length of 40 mm. The platinum wires, I and I, 
serving as electrodes were 1 mm. in diameter, and extended beyond the interior 
surface of the glass (into which they were sealed) for only 3 mm. in length. They 
could be well covered, and the voltameter tubes filled to one-third their capacity, with 
oidy about 2 c cm. of the acidulated water. By careful tilting of the apparatus 
laterally it was found to be possible to so regulate the pressure of mercury at 
the ends of the deliveiy tubes, and therefore the gaseous tension in the two 
voltameter tubes, that the acidulated water was not forced over from the one to the 
other, which, had it occurred, would have allowed admixture of the two gases ; this 
recpaired constant watching, however, and there was needed from time to time a little 
