54 On the Decomposition of Iodides by Nitric Acid. 
burns with a clear flame, in which blue rays are often per- 
ceived. Its specific gravity is 1°75; it can be filed, and takes 
an excellent polish ; it resists the action of the air tolerably well, 
though not so well as zinc. When distilled in a rapid current 
of hydrogen, some metallic dust is carried away, which remains 
suspended in the hydrogen ; and if this be set fire to, it burns 
with one of the most beautiful flames which can be conceived. 
Deville and Caron are still engaged in an investigation of the 
physical properties of magnesium, and experiments are in pro- 
gress on the reduction of the alkaline earths by means of carbon. 
In a note on ozonometry, M. Bineau* seemed to attribute to 
nitric acid the property of liberating iodine from iodide of po- 
tassium in the cold, and in the presence of water. Béchampt 
adduces a variety of facts which show that this is not the case, 
if the nitric acid be pure. 
If to a given volume of dilute solution of iodide of potassium, 
which has been mixed with starch-paste, a drop of nitrie acid 
such as is usually found in laboratories be added, the mixture 
becomes immediately blue ; if to another volume of the iodide 
solution there be added even a great excess of the same nitric 
acid diluted, but which has had carbonic acid passed though it 
in the dark to expel nitrous acid, the mixture does not become 
blue ; the same is the case on adding to the iodide solution pure 
nitrate of potash and sulphuric acid. But this becomes blue 
also if the nitrate of potash has been melted, or has been in 
contact with organic substances, or if traces of nitrite of potash 
be added. Ozonometric paper, therefore, does not become blue 
under the influence of pure dilute nitric acid; the coloration 
must be attributed to the nitrous acid always contained in con- 
centrated nitric acid which has been prepared some time. 
Millon showed long ago that pure nitric acid, free from nitrous 
acid, did not liberate iodine from iodides, or sulphur from sul- 
phides ; but it has not been stated what is the action of nitrous 
acid on iodides. Béchamp examined this point, and found that 
the action of nitrous acid gave rise to the formation of nitric 
oxide, and was a convenient method of preparing this gas. He 
mixed an equivalent of nitrite of potash, and an equivalent of 
iodide of potassium dissolved in water, in an appropriate appa- 
ratus, and having expelled all the air by means of carbonic acid, 
added a few drops of sulphuric acid; a rapid evolution of gas 
ensued, which reddened in the air, and was completely absorbed 
by protosulphate of iron. This was binoxide of nitrogen, which 
could only have arisen from the action of nitrous acid on the 
* Phil. Mag., October 1856. Comptes Rendus, July 21, 1856. 
+ Comptes Rendus, Aug. 18, 1856. 
