202 Prof. Silas W. Holman on the Effect of 



and one was filled with concentrated sulphuric acid. iTwas 

 placed about a metre above J. The two were connected by 

 two glass tubes, a and b, each containing a stopcock, and had 

 other tubes arranged as shown in the sketch. To withdraw 

 the sulphuric acid from J" into K, and to replace this by the 

 C0 2 , it was simply necessary to connect P to the gas-holder 

 or generator, to close e and/, to open c, to exhaust the air 

 from K by an aspirator, and, opening the cock in h, to allow 

 the H 2 S0 4 to be transferred to any desired extent. This being 

 accomplished, d and e were closed and the generator discon- 

 nected. When a measurement is in progress, the C0 2 passing 

 at a uniform rate from J through H must be replaced by 

 sulphuric acid from K through a. This flow is regulated by 

 a tangent-screw motion on the cock/, until the liqaid drops or 

 runs into J" at such a rate as to displace not only the necessary 

 amount of C0 2 , but slightly more than this, the excess esca- 

 ping slowly through c and a fine orifice at P. This arrange- 

 ment maintains an almost constant pressure in J ; and as the 

 pressure is thus always outward, there can be no inward leak- 

 age of air either during the measurements or at other times. 

 The gas, after passing, always with this slight excess of pres- 

 sure within, through H, Z, enters the glass bulbs gg ; and the 

 pressure p 1 at entrance is measured by the. barometric height 

 at the time plus the pressure indicated by the gauge at R y 

 read by the cathetometer. The bulbs gg were spherical enlarge- 

 ments of about three centimetres in diameter of a glass tube of 

 about half a centimetre in diameter. The contents of these 

 bulbs would be transpired by the capillaries once in about fifteen 

 minutes. The tube gg and the capillary were connected into 

 one piece at A by melting them together, and a similar solid 

 connection was made at B to an exit-tube. The tubes CD 

 and h h were similar in all respects to A B and gg, the capil- 

 laries being of very nearly the same length, and cut from the 

 same piece of tubing, which was one of those used in the 

 experiments of 1876. The tube connecting B to hh was 

 of about 3 millim. internal diameter and 50 centim. length, 

 and at its middle point contained a branch, which extended, 

 with one joint of the kind described, to the gauge B, which 

 in connection with the barometer served to measure p 2 . 

 The gas at exit from C passed about 50 centim. of 3 millim. 

 tubing to the point G, where a side branch led to the gauge F, 

 which gave the pressure p 3 . Passing by G, the gas moved 

 forward past N to the aspirator 0* and then escaped. The 



* Richard's jet-aspirator was used. See Amer. Jour. Sci. [3] viii. 

 p. 200 ; Chem. News, xxxiv. p. 141 ; Trans. Amer. Mining Eng. vi. p. 492 

 (1879). 



