800 
MR. BRODIE ON THE CONDITION OF CERTAIN ELEMENTS 
When phosphorus and iodine are used instead of iodine in this experiment, no essen- 
tial change has taken place in the causes which determine the combining condition 
of the particles, but a particle of phosphorus now stands in the same relation to the 
baryta as the particle of iodine in the other experiment, thus : — 
P IBaO=IBa-hPO. 
j 
Now if thus intercalating the particle of phosphorus transfers the action from the 
iodine to the phosphorus, so also intercalating a particle of oxygen might transfer the 
action from the iodine to the oxygen itself, which would now be the truly oxidized 
body, provided of course that the particle of oxygen thus intercalated were a body 
which stood to the other particles with which it was in contact, in the same chemical 
relation as the iodine and phosphorus in the other changes ; nor do I see that this 
substitution of the oxygen for the iodine is more truly extraordinary than the sub- 
stitution of the iodine for the phosphorus. Indeed, if we inquire into the causes of 
chemical change, the two would depend essentially upon one and the same fact, 
namely, a chemical difference between the particles of the element. In the one case 
we have the chemical division of the element, in the other the chemical synthesis to 
explain; and to give a philosophical account of either fact we must assume alike the 
existence of a chemical difference between its particles. Now, when we substitute 
peroxide of barium for baryta in the iodine experiment, this very intercalation of the 
oxygen has been effected, and the conditions of the change been fulfilled, the polar 
cycle being completed, thus : — 
h — + 
I BaO 0=IBa-l-02. 
) 
In fact, when water is poured upon a mixture of peroxide of barium and iodine, a 
violent evolution of gas occurs, and the same when chlorine is led into water con- 
taining the peroxide, or when the peroxide is thrown into a solution of hypochlorite 
of lime in acetic acid. 
This experiment with iodine is so important, that I shall give at full length the de- 
terminations of the quantity of gas evolved in this reaction. The experiment was 
made in the small bulb-apparatus already described, p. 779- 
The weighed peroxide and weighed iodine were mixed in the flask, the bulb being 
filled with distilled water ; the apparatus was weighed, and the water then allowed to 
descend on the mixture. The loss on again weighing the apparatus is the oxygen 
evolved. The same precautions are to be taken in the experiment as in the oxygen 
determination. 
The peroxide used in the following experiments was the peroxide Q, containing 
8‘58 per cent, of oxygen; 100 parts of this peroxide require 138 parts of iodine as 
one equivalent to the oxygen it contains. The first of the following Tables contains 
