SULPHUROUS ACID ON HYPONITRIC ACID. 75 
while a white substance, presenting the properties of sulphate 
of ammonia, remains. 
Nitric, oxalic, and acetic acids decompose this substance. 
Hydrochloric acid gives a species of aqua regia. Concentrated 
sulphuric acid is without action on it in the cold; advantage of 
which property has been taken to obtain its density in the solid 
state: it is 2°14. Aided by heat it dissolves in sulphuric acid 
without decomposition ; but the mixture is not immediately 
effected, and the difference in density is such that the acid floats 
some time on the fused substance. When the mixture is com- 
plete, it possesses a greenish-yellow colour. The production of 
this colour is so very sensible a character, that traces of this 
substance in sulphuric acid may be recognized by its occurrence. 
The two substances are not separated by heat, both distilling 
together. If the sulphuric acid be in large excess, the whole is 
liquid and colourless while cold ; in the contrary case, the mass 
is solid, semi-transparent, almost colourless, and retains only a 
slight tint of yellow, with more or less green. In the hydrated 
state, or already combined with sulphuric acid, it dissolves, 
however, in sulphuric acid in the cold. 
The solution can be effected in all proportions, and what is 
very remarkable, in returning to the solid condition it uniformly 
produces crystals, possessing great analogy in form. The larger 
the proportion of sulphuric acid in the crystals, the more fusi- 
ble they are. The melted mass is commonly very viscid, and it 
is doubtless for this reason, that when once liquid, it is very tardy 
in resuming the solid state. One of these solutions, which 
melted at about 60° cent. (140° Fahr.), remained liquid at a 
temperature which was not above 10° cent. (50° Fahr.). When 
agitated, solidification is determined ; the temperature rises con- 
siderably, as might be expected, and small, heavy white tufts, 
suddenly appear dispersed through the liquid, and remain sus- 
pended in the place where they were produced. The presence of 
oneof these determines the rapidformation of many others. When 
the pure substance is exposed to air, it attracts moisture from 
all parts of its surface. The azotized compound is partly de- 
stroyed at the surface, sulphuric acid remaining; but the sub- 
stance is so compact, and so feebly acted on by the free sulphuric 
acid, that the quantity of the latter augments very slowly, and 
only until the acid has absorbed a certain quantity of water, 
On heating, a homogeneous mixture is obtained, forming a so- 
