ON PYROXYLIC SPIRIT, &c. I3I 



This experiment was repeated with a strong aqueous solution of iodide of po- 

 tassium, the water containing one-tliird of its weight of the salt, and being placed 

 in B, all other circumstances being the same as before. In five minutes thel^e 

 was a trace of acid on the asbestus between B and C, with alkali at the nega- 

 tive pole. In fifteen minutes there was also a trace of acid at the positive 

 side of the solution in B, and this was quite decided in twenty minutes, and 

 more so than that on the asbestus, whilst at the positive pole there was still 

 no acid. In forty minutes the acid reaction at the positive side of B was power- 

 ful, whilst all the other acid reactions were slight or doubtful. On the negative 

 side of B, and from that to the negative pole, alkali was observed. A shght dis- 

 coloration appeared in C, and none in A or B. 



With a power of seventy-two pairs of 4-inch plates, and the strong solution 

 of iodide in B, and water in A and C, the three vessels being glass cups, each of the 

 capacity of one-fourth of an ounce, there was slight acid at the positive pole in five 

 minutes, and strong acid at the positive side of B in fifteen, with alkali at the nega- 

 tive pole and on the adjoining asbestus. During the forty minutes which the experi- 

 ment lasted, the acid reaction in B continued to increase and became very power- 

 ful, whilst that at all other places where it was noticed continued slight. A dis- 

 coloration of the water in C had been noticed in fifteen minutes, with none in B 

 or A then or for half-an-hour, and in forty minutes the liquid in C had assumed 

 a pretty deep red throughout, and smelt strongly of iodine, whilst in B there was 

 only a slight yellow tint confined to a single spot on the positive side of its upper 

 layer, and no smeU of iodine at aU. 



When the liquid in C was concentrated by heat tillit was colourless, it was 

 found, when the larger voltaic power had been used, to contain a trace of iodic 

 acid ; but where the smaller had been employed the nature of the acid in C was 

 rather ambiguous. As the iodic acid was, to all appearance, referable to a secon- 

 dary action, and it was of some consequence, with a view to the true explanation 

 of the phenomena, to ascertain with certainty that the acid formed in B under 

 the voltaic influence was hydriodic acid and not iodic acid, the following experi- 

 ment was made. 



Water containing ^d of iodide of potassium was placed in the tube B, and 

 pure water in the tubes A, C, and D, Fig. 4, the whole being connected by asbes- 

 tus, and A made negative and D positive by 72 pairs of 4 inch plates. In ten 

 minutes there was slight acid at the positive side of B, and on the asbestus be- 

 tween C and D, and at the positive pole in D, but none in the liquid in C. In 

 twenty minutes the acid reaction on the positive side of B was strong, with a less 

 marked on the asbestus between C and D, and alkali on the negative side of B. In 

 fifty minutes the hquid in D had acquired a uniform pretty deep brown, whilst those 

 in C and A were not at all discoloured ; and in B there was merely a pale yeUow 



