and on the crystalline solid formed in that Process. 117 



very little escape of nitrous vapour; the solution becomes pale 

 yellow like nitrous acid. At +60° Fahr. gas partially escapes, 

 and this is again reabsorbed as the temperature falls. At 

 + 35° to 20° Fahr. no gas escapes from the solution, nor can 

 concentration of the solution expel all the nitrous acid. 



7. When the solid is dissolved in oil of vitriol of sp. gr.l-060, 

 the immediate decomposition of the nitrous acid is prevented : 

 the process goes slowly on. About fourteen days are necessary 

 for the complete evolution of all the deutoxide of azote arising 

 from this decomposition ; bubbles of gas escape during the 

 whole time ; yet when these cease, nitrous acid is found in 

 the solution; no agitation drives it off; nor will sulphurous acid 

 gas decompose it. 



8. If a current of sulphurous acid gas is passed through 

 a green-coloured solution of the crystalline solid in water, 

 this colour is discharged, and the solution becomes pale yel- 

 low; effervescence takes place throughout the whole liquid; 

 nothing but deutoxide of azote escapes. 



The action of water in forming sulphuric acid, seems to 

 me to have never been rightly understood. It is well known 

 that the above-mentioned white solid cannot be produced by 

 nitrous vapour and sulphurous acid gas, unless water is present. 

 What then is the action of water? I suppose that by it, red 

 nitrous vapour is decomposed into nitric and hyponitrous 

 acids. The nitric acid is immediately decomposed by the 

 sulphurous acid gas, sulphuric acid and hyponitrous acid re- 

 sult ; these unite with the water and form the white crystalline 

 solid. I explain the above phaenomena, and some facts which 

 occur in the manufacture of oil of vitriol, as follows : — 



It is evident from Experiment (2) that the effervescence is 

 due in part to the escape of nitrous vapour; and deutoxide of 

 azote also escapes, arising from the decomposition of hypo- 

 nitrous acid, by the action of water. In oil of vitriol this de- 

 composition is either prevented or retarded ; hence there is 

 less of the red-fume appearance according to the density of 

 the oil of vitriol, none appearing in concentrated oil of vitriol. 

 At the moment of solution of the solid in water, the hyponi- 

 trous acid gives it a blue colour ; but this acid is immediately 

 decomposed into the nitric and nitrous acids, and deutoxide of 

 azote. The nitrous acid being yellow, converts the blue to 

 green, and this last colour is probably deepened by the pre- 

 sence of deutoxide of azote, such being the fact, with respect 

 to saturating nitrous acid with deutoxide of azote. But the 

 nitrous acid is yellow; hence as this preponderates, the solu- 

 tion finally becomes yellowish. 



The nitric acid, and a portion of the deutoxide of azote are 



