142 
THE VOYAGE OF H.M.S. CHALLENGER. 
1 1 1 r is now expelled by keeping the water in the pear-shaped bulb in ebullition for a 
sufficient time. As soon as all the air has been presumably expelled by the steam, the 
india-rubber tube at the upper end is closed by the clip, the lamp withdrawn, and the 
(narrow) exit-tube sealed up. The stem carrying the bulbs is now pushed down into the 
wat' r, sons to establish a communication between the flask and the bulbs through the 
1 hole, and the flask heated over a flame or in a water-bath, so as to boil out the 
di"' dved gases, which, of course, if the bulb apparatus is of sufficient size, can be effected 
a temperature considerably below 100° C., and without the pressure inside ever coming 
up to one atmosphere. After one or two hours’ boiling the gases may be assumed to be 
■ xp'11'd, and with some practice it is quite possible so to carry out the process that the 
whole of the gas is in the upper bulb while the lower is filled only with water and 
i. -*> that one can clip the india-rubber joint and seal off the gas -bulb immediately 
b '\v the water, and thus secure the whole of the extracted gas in a sealed-up glass 
vessel. 
This method, which had worked so well in Jacobsen’s hands, was adopted by Mr. 
Buchanan, and applied by him during the voyage to a large number of recently-drawn 
ten. He generally operated upon 855 or 900 c.c.,inafew cases upon 500 c.c. of sea- 
v. iter. A number of the many gas samples which he brought home he analysed him- 
- If by m* ans of a Doyere apparatus. The majority, however, were placed in my hands 
tie- Din etor of the Challenger Expedition Commission, with instructions to “analyse 
■ cm. " It was only after I had already made a considerable number of such analyses 
i it I became aware of the existence in Mr. Buchanan’s journal of the necessary data 
’ >r tin* determination of the absolute volume of the gases extracted. Fortunately, 
• • • * b ■ • u _■ 1 1 my gas apparatus (which will be described presently) was contrived so that 
; - v. . 'i king did not involve any absolute determinations of the temperature or pressure 
the gases analysed, I had always taken these readings and preserved them. And 
m addition, no bell of the gas had ever been allowed to go to waste, my analytical 
t< - enabled me to calculate the absolute volume of the gases as contained in Mr. 
I* eh nan - bulb I liese, however, were all liable to a correction, necessitated by the 
fart that Mr. I Indianan did not find it convenient to force the whole of the boiled-out 
: • . the gas bulb, but allowed a small fraction of it to remain on the wrong side 
’ ■ point of -f iling. But he took care to measure these portions of lost gas under 
■' * '"editions to which they were subjected at the moment of the sealing-up, and to 
- -r tie * e volumes in his journal. Fortunately the emptied gas-bulbs had been 
* 1 ■ r ■ ' by me (chiefly on account of their labels), and it was easy to measure their 
codU nts by me ury, *<» that in the vast majority of cases I was in a position 
to oHert the calculation of the absolute volume. 
I ■ ic proceed to d* - ribc the apparatus which I used for making the 
analyse*. 
gas 
