478 ME. J. B. I.WVKs. DB.GHLBEBT, wi> DE. IM'< li ■ 



seen better in figs. I & 5, Hate XII., which represent, respectively, the plan and the 

 vertical section of the glazed Btone-ware lute-vessel used Ln 1 358. Another glass tube (J * 

 passes to the bottom of the vessel (figs. I & 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 L858 (fig. I. Plate XII.) -hows tie 

 for the mercury, the four widened and deepened points of it for the passage of the tub< 

 under the shade (ofwhich however three onhj were used), and the hole ,,' 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 lor the 

 reception of the shade and of the mercury luting, and for the passage of the tub. 

 Fiffure 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 ri. 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 XIII., 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 Ajiparattis. 



If the stopcock below a (fig. 1, Plate XIII., 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 qrs, «r r/ ;•' s\ 

 above the level in the vessel A, and at the same time the air begins to escape by the 

 tube c d e, or c' d' e', 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 

 i k 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 xl-2]x^=l-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 

 q r s, or q' r' 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 q r s and c d e. 

 fig. 1, Plate XIII. (that of the former being the higher), be less than the minimum height 



