258 
MR. J. J. MANLEY ON THE APPARENT 
more or less correctly, the initial stage of the whole reaction, but it is quite clear 
that other and perhaps somewhat involved and little understood chemical changes 
are induced some time later, the period varying greatly with the conditions of light, 
heat, &c. 
Seeing then that a close study of one apparently simple chemical reaction led to such 
totally unexpected conclusions, and remembering that the nature of some of the other 
reactions made use of by Landolt cannot, in all probability, be simpler than that of 
the reaction which we have investigated somewhat imperfectly here, it would 
naturally appear that a more perfect knowledge of the chemical changes which 
were made use of by Landolt, combined with the application of the methods we 
have advocated and practised for refined weighing, would enable us to explain at 
least some of those obscure points which arise in Landolt’s memoir. We now 
pass to the consideration of one final experiment and the results which were obtained 
by its aid. 
(lO) Of some Results obtained with Barium Chloride and Sodium Sulphate. —AVith 
the object of securing additional and confirmatory evidence in support of the correct¬ 
ness of the views which we had now formed, a final experiment was devised and 
carried out. 
It will be universally admitted that the reaction which follows the mixing of barium 
chloride and sodium sulphate solutions is, for all practical purposes, instantaneous and 
complete. We are not, however, aware that either this or other similarly rapid 
and complete reactions have been deliberately and systematically made use of by 
preceding investigators ; but the results we have obtained and described force us to 
the inevitable conclusion that the only reactions we may legitimately make use of for 
our present purposes are just those in which the chemical changes terminate within 
a reasonably brief period; further, the products of the reaction must be of such a 
nature that the pressure within the vessel is not appreciably altered. 
For the purpose of carrying out the final experiment two re-blown Jena glass vessels, 
similar to those used in the preceding experiments, were prepared ; but as it was not 
intended to duplicate the experiment, one vessel only was supplied with an inner 
flask ; the other vessel was used simply as a counterpoise. The reaction vessel was 
charged with equivalent quantities of almost saturated solutions of highly purified 
barium chloride and sodium sulphate, the latter being placed in the small inner flask ; 
the counterpoise was charged with the proper weight of water ; the reaction vessel and 
its counterpoise were then sealed, their volumes and weights determined and afterwards 
equalised ; finally the vessels were cleaned. All these necessary operations were 
performed in the manner described on pp. 231 and 248. The subsequent weighings were 
conducted under precisely the same conditions and with the same precautions as those 
introduced and observed during the final experiments with silver nitrate and ferrous 
sulphate. The results obtained during the course of this experiment are summarised 
and set forth in the following table :— 
