478 MR. J. B. LAWES, DR. GILBERT, AND DR. PUGH ON’ 
seen better in figs. 4 & 5, Plate XII., which represent, respectively, the plan and the 
vertical section of the glazed stone-ware lute-vessel used in 1858. Another glass tube (¢’) 
passes to the bottom of the vessel O (figs. 1 & 2, Plate XIV.), for the purpose of with- 
drawing the condensed water which collects in it. 
The plan of the stone-ware lute-vessel used in 1858 (fig. 4, Plate XII.) shows the groove 
for the mercury, the four widened and deepened points of it for the passage of the tubes 
under the shade (of which however three only were used), and the hole 7! at the bottom, 
for the reception of the tube for carrying off the condensed water. This lute-vessel is 
made of hard-baked and well-glazed stone-ware, and is, in fact, simply a shallow dish 
with double concentric sides, the space between which latter forms the groove for the 
reception of the shade and of the mercury luting, and for the passage of the tubes. 
Figure 5, Plate XII., is a vertical section of the stone-ware lute-vessel, from A to B, 
fig. 4, through two of the widened and deepened portions of the groove, and through 
the hole n'. Figure 6, Plate XII, is also a vertical section of the lute-vessel, but from 
C to D, fig. 4. 
The Woulfe’s bottle T, fig. 1, Plate XTIII., and T’, fig. 1, Plate XIV., is for the supply 
of carbonic acid, and will be referred to, more fully, in the following subsection I. 
I.— Use of the Apparatus. 
If the stopcock below a (fig. 1, Plate XIJII., and fig. 1, Plate XIV.) is opened, water 
flows into the vessel A from a large reservoir with which the leaden tube a is in con- 
nexion. As the pressure increases, the water rises in the safety tube gr's, or g'7's’, 
above the level in the vessel A, and at the same time the air begins to escape by the 
tube cde, or c'd'é', to force its way through the sulphuric acid in the bottles B, C, then 
to traverse the tube D D, containing the pumice saturated with sulphuric acid, to 
bubble through the solution of carbonate of soda in E, and finally to enter the shade F 
by the bent and jointed tubes g, h; and from the shade it passes out through the tube 
ik and the bulb-apparatus M containing sulphuric acid, into the external air. 
The minimum pressure required to’ produce this passage of air, expressed in the 
height of a column of mercury which it would sustain, is equal to the sum of the pro- 
ducts obtained by multiplying the height of each fluid through which the air has to 
pass by the sp. gr. of the same, divided by the sp. gr. of mercury, or 
[(2°5+2°5-+1-0) x 1-85+2-5 x 1-2} ;45 = 1-037 inch, 
in which 1-2 is the sp. gr. of the carbonate-of-soda solution. 
The difference between the height of the water in the vessel A and in the safety-tube 
qr, or g'7’s', must always be equal to the weight of the mercury column obtained in 
the manner just indicated, multiplied by the sp. gr. of mercury. 
If the difference between the height of the highest points of the tubes grsand ede, 
fig. 1, Plate XIII. (that of the former being the higher), be less than the minimum height 
