OF THE ATOMIC WEIGHT OF ALUMINUM. 
1027 
and of aluminum (the latter from its weight), calibration of the bulb and tubes after 
the experiment was over completed the data necessary to determine the volume of 
air which the apparatus contained at the beginning. The aluminum was now made to 
slide down into the bulb, the end of the gas-delivery tube (c) having been brought 
under the mouth of the measuring flask. Over-rapid evolution of hydrogen and any 
considerable rise of temperature were prevented, partly by tilting the bulb so that the 
little piece of aluminum rested against one side and exposed but a part of its surface 
to the action of the liquid, and partly by cooling the outside of the bulb with water; 
while, on the other hand, it sometimes became necessary to gently warm the liquid 
towards the end of the experiment. To guard against more than traces of aqueous 
vapour being carried away with the hydrogen, a current of ice-water was kept up 
through (d). As soon as the last of the aluminum had disappeared, leaving the liquid 
quite clear, (c) was brought up into a nearly vertical position, and the apparatus left 
to itself until the temperature of the room had been attained. The barometer and 
thermometer, height of mercury in (c) above that in trough, and level of mercury in 
neck of measuring flask (after the last traces of moisture had been removed from the 
hydrogen by means of a stick of caustic potash), with its height above that in trough, 
were now read and recorded. Lifting (c) straight up from the trough, the mercury in 
this tube was got out by running a wire up and down in it, and inverting it, the 
whole of the remaining space in (a), (//), and (c) was filled up with alkaline lye of the 
same strength with that already contained, this liquid being run in from a graduated 
burette through a slender tube funnel, and the volume used noted, so as to show how 
much liquid had been already present. The apparatus being now emptied, washed 
out, and calibrated (with water, instead of mercury, on account of the difficulty of 
getting the interior quite dry), the volume of gas remaining in it at the close of the 
experiment was had from the difference between the total capacity (to the level of the 
mercury in (c)) and the volume of liquid which the bulb had contained at the close of 
the experiment, these taken together with the data for pressure and temperature. 
On account of slight rise of temperature during the solution of the metal, the 
volume of hydrogen left in the bulb and tubes was always less than the air in the 
same at the beginning; and, after reduction to normal temperature and pressure, the 
difference had to be subtracted from the volume of gas collected in the flask. 
In order to connect the weight of the aluminum with the weight of the hydrogen, 
the latter being obtained from its observed volume and Regnault’s determination of 
its density, it was necessary that the weight of the metal should be absolute, or in 
terms of equal value with those used in Regnault’s researches ; hence, as has been 
already stated, the weights used were such as had had their real value determined, 
and the precaution of double weighing was applied. The quantities of metal used 
being small, the centre of gravity of the balance beam was so adjusted as to give 
great sensitiveness. 
In calculating the weight of the hydrogen from its volume, the difference in the 
(5 Q 2 
