144 
THE VOYAGE OF H.M.S. CHALLENGER. 
menis us inside. The volumes corresponding to the several points of the scale are 
>1 ■ linin' d by calibration. The short narrow tube which forms an appendage to the 
■U"Mi of the burette, serves to insert it, by means of a perforated india-rubber stopper, 
an aperture in the centre of the bottom of a water-bath, the front and back of which 
.re made of plate glass. This bath holds a fixed position on a substantial table, and 
communicates with the service-pipes in such a manner that a continuous current of 
w ter from these flows through it, while in use, to maintain an approximately constant 
temperature. 
The exploder is a wide tube with platinum wires soldered-in, provided with a stop- 
C"«-k and capillary (J-tube at the upper end, and connected below with a mercury reservoir 
like the measurer. It is fixed vertically to a wooden stand. Between it and the 
measurer stands a pn< umatic trough, made out of a block of mahogany, which is provided 
with two wells of suitable size and shape to accommodate the lj-tubes of the measurer 
and of the exploder respectively. A special similar trough, with one well, is reserved for 
the pipette , the construction of which will easily be understood from the figure. It 
differs from the original Doy&re, or rather, Ettling, pipette (for it was he who invented 
the instrument) chiefly in this, that the sucking and blowing is effected by means of 
i small mercury reservoir connected with the gas reservoir by an india-rubber tube, 
and that the flow of the gas or mercury or liquid reagent is governed by a stop-cock in 
the capillary part. The vertical side tube and small mercury reservoir soldered on to 
tie horizontal part of the capillary tube may be dispensed with (in fact it did not exist 
in the original model), but are convenient additions, as will readily be understood 
(if not divined at first sight) by the following description of the mode of using the 
apparatus. Long after all our gas analyses had been finished, Mr. Lennox devised an 
improved form ofthe pipette, which is represented in Fig. VI. From this figure it will 
p ui ly be understood that the supplementary mercury reservoir is dispensed with, the 
metal in the bulb serving to push the gas out of the lj-tube. 
malyse a sear-water gas il is transferred from t he cylindrical tube containing it to 
a short wide test-tube made of stout glass, ail operation which is greatly facilitated by 
the deep wells in the pneumatic trough of the measurer. About one-half of the gas is 
’ ■ ; 1. d into the measurer, which is so manipulated that at the end the whole of the 
U and the capillary part following it are filled with mercury. During this operation 
the t. mm ride tube (which, like all the rest of the burette, must be understood to have 
been < ju it«* full of mercury before commencing) remains closed. The mercury reservoir is 
‘ ' ' ft* 1 -■> ■ to bring tie* menisci in it and in the burette into nearly the same hori- 
I' n . tli< "top-cork of the side tube opened, and the reservoir now carefully ad- 
"tl. it tin men-ury in the side tube is exactly on a level with that in the 
ome practice this can be effected very accurately by the eye, 
' ' ‘ ■ "1 *• (which, of course, i.* required for reading the position of the meniscus 
