530 Mr, PoRRETT on the nature of the Salts 
of employing conducting wires of copper instead of platina, 
and found that the only difference in the result was, that the 
reddish brown triple prussiate of copper and iron was formed 
instead of the blue triple prussiate of iron, which effect was 
owing to the oxide of copper formed at the positive pole com- 
bining with the peculiar acid of the triple prussiates. 
The next experiment which I shall relate is still more con- 
clusive. I dissolved the triple prussiate of barytes in cold 
water, of which it required i8co times its weight, I divided 
this equally, and by an experiment made purposely with one 
portion, ascertained the exact quantity of diluted sulphuric 
acid necessary to throw down the barytes from the other ; 
this quantity was equal to 2,53 grains of real sulphuric acid 
for every ten grains of the salt employed; then filling a bottle 
with the second portion so as only to leave room for the acid 
to be added, I poured into it the quantity of acid previously 
ascertained, closed the bottle immediately, and left the sul- 
phate of barytes to subside to the bottom ; when this had 
taken place, the clear supernatant fluid was examined, and 
found to be the pure acid of the triple prussiates. It has the 
following characters : 
It is of a pale lemon yellow colour ; it has no smell ; it is 
decomposed by a gentle heat, or by exposure to a strong 
light ; prussic acid is then formed, and white triple prussiate 
of iron, which quickly absorbing oxygen from the air, change# 
to blue triple prussiate. It forms directly with alkalies, earths, 
or oxides, the salts termed triple prussiates. It displaces the 
acetic acid from all its combinations in the cold, and forms 
triple prussiates with the bases before united to that acid. It 
is capable of expelling all other acids from their soluble 
