PEOFESSOE BUNSEN AND DE. H, E. EOSCOE’S PHOTO-CHEMICAL EESE.UICHES. 30 7 
amounted to 2544 cub. cent., and the quantity of anhydrous acid contained in the elec- 
trolytic liquid had decreased from 30 to 21 ‘4 per cent. On continuing the experiment 
on the fifth day with fresh hydrochloric acid, the action attained a maximum of 20 '40 
after the gas had been led through for fifteen minutes. This maximum action remained 
constant in all subsequent experiments with renewed quantities of acid, and in each case 
a short saturation sufficed to bring the gas to the maximum degree of sensibility, in 
which the action was 26’49. 
The second series of experiments gives, as may be seen, the same general results as 
the one just described. 
From these and a large number of similar experiments which we have made in the 
course of the testing of the instrument, the following conclusions may be drawn : — 
(1) When the quantity of hydrochloric acid contained in the liquid electrolyte has 
decreased from 30 to about 23 per cent., the evolved gases are no longer fitted for com- 
parative photo-chemical measurements. 
(2) In order to attain the first constant action, at least 2000 cub. cent, of gas must 
be passed through the small vessel of 7 cub. cent, capacity, containing 1-8 cub. cent, of 
water. 
(3) By continued saturation the action increases up to a certain point at which a per- 
manently constant maximum is reached, which in our apparatus was not attained until 
more than 6000 cub. cent, of the chlorine and hydrogen mixture had passed through 
the insolation-vessel. 
(4) The attainment of the necessary equilibrium in the apparatus is much accelerated 
by allowing the water to remain in contact with the gases during the night. Were the 
saturation continued without intermission, a much larger quantity of gas would have to 
be led through the apparatus before the maximum action is attained, than was required 
in the foregoing experiments. All the attempts which we have as yet made to shorten this 
most tedious period of preparation necessary for the execution of photo-chemical measure- 
ments with chlorine and hydrogen have proved fruitless. 
Long experience has shown that the apparatus is most conveniently filled by the 
following manipulation. The operation is commenced in the morning by filling the 
evolution-tube a, fig. 2, udth about 55 cub. cent, of hydrochloric acid of spec. grav. 
1T48, and leading through the apparatus the gas evolved from this cell at such a rate 
that about two bubbles pass through the washing-bulbs and insolation-vessel every second 
of time. In the afternoon, the acid, which can be reduced by 7 per cent, of its original 
volume, is changed, and the operation repeated, with the important exception that the 
gas evolved during the first hour, containing air and excess of hydrogen, is not allowed 
to pass through the apparatus, but escapes through the manometer by the tubes vv, 
p into the condenser G. The instrument, protected from all exposure to light, is then 
allowed to stand during the night with the stopcock closed, and the operations are com- 
menced in the morning anew, care being always taken to allow the impure gas to escape 
during the first hour of evolution. During the intervals of saturation, the photo-chemical 
