CHAP. I. ] THE EQUIPMENT OF THE SHIP. 45 
shown in Fig. 6, which enables the potash to be eliminated from 
the apparatus. The position of @ is then brought back to that 
of Fig. 7,and the gas remaining in the capillary swept out by 
mercury and measured as before. 
If the oxygen is to be determined by absorption, the manip- 
ulations are exactly the same as in the case of carbonic acid, 
alkaline pyrogallic acid being used instead of caustic potash. 
If the oxygen is to be determined by eudiometry, then, after 
the carbonic acid has been absorbed, the gas remains in the 
eudiometer, the stop-cocks ¢ and } being closed. The stop-cock 
d is now opened, and @ turned the reverse way to that shown 
in Fig. 6—that is to say, with the side communication [3 y com- 
municating with the capillary above a. The capillary is thus 
emptied of mercury, and the hydrogen evolving apparatus is 
connected with y by an india-rubber tube, and the hydrogen 
allowed to stream through a, d,¢ until all the air is swept out ; 
the stop-cock d is then closed, and a brought back to the posi- 
tion in Fig. 6, when the gas enters m. When enough hydro- 
gen has passed in, a@ is brought to its position in Fig. 7, and the 
hydrogen apparatus is dispensed with. Mercury is now pour- 
ed into e, and d@ opened, and the hydrogen in the capillary 
driven into m, its place being taken by mercury. The hydro- 
gen is now passed over into the measuring-tube and measured, 
and the explosion is made. . 
When the analysis is finished, the mercury is emptied out of 
the tubes; the parts A and B are separated from each other at 
J by relieving the india-rubber connection, and from the box 
by taking out the screws x, a,x. The mercury receptacle D is 
removed, and A and B deposited, each in its own wing of the 
box, to which it fits, and is fixed by the bolts z,z. The whole 
gas-analysis apparatus is now contained in a box which measures 
when closed, over the outside, 19 inches by 9 inches square. 
Fig. 8 represents an apparatus for preparing oxygen, hydro- 
gen, or knallgas, for use in gas analysis. It is of the well- 
.—4 
