AND OF SALTS OP THE PEROXIDE OP IRON. 261 
sian blue from the solution of the percyanide. Warming 
of the solution hastens the reaction of the lithic acid. 
Creosote even surpasses lithic acid by its deoxidizing ac- 
tion on persalts of iron. Cinchonine and morphine act in a 
similar manner, but not so rapidly. Nascent hydrogen, in 
contact with a solution of persalt of iron, imparts to it the 
property of precipitating prussian blue from the solution of 
the percyanide. 
Nitrous acid, nitric oxide, sulphurous acid, and the com- 
binations of hydrogen with selenium, phosphorus, arsenic, 
antimony and tellurium, behave in a similar manner. 
Dilute solutions of oxalic acid, nitrate of iron and ferrid- 
cyanide of potassium were mixed and conveyed into a 
flask, into which nitric oxide, sulphuretted and phosphoret- 
ted hydrogen were introduced. According to the preceding 
statements these gases precipitate prussian blue from a li- 
quid containing only nitrate of iron and percyanide ; in the 
mixture, however, containing oxalic acid, they cause no 
such precipitate, but in order to obtain this negative result 
it is requisite that there should not be too little oxalic acid 
present in the solution. 
With respect to seleniuretted hydrogen, oxalic acid is not 
able to prevent entirely its action on the mixture, which im- 
mediately becomes blue. When a solution of the percy- 
anide is placed in contact with lithic acid and oxalic acid, 
no blue coloring is produced by a persalt of iron, however 
long the substances may have been together, nor does heat- 
ing in any way assist. 
Oxalic acid likewise prevents sugar and other organic 
matters from altering the percyanide and the persalts of 
iron in the above manner, nor is there any prussian blue 
precipitated, even on adding nitrous acid to a mixture con- 
taining percyanide, nitrate of iron and oxalic acid. 
Besides the interest which these experiments offer, they 
likewise lead to ready methods of detecting nitric oxide, 
nitrous acid and sulphurous acid. Moreover, since the or- 
