120 Dr. Dana on the Manufacture of Sulphuric Acid, 



According to the above view of the formation of sulphuric 

 acid, there ought not to be any nitric acid in the liquid drawn 

 from a lead-house : it ought to be wholly decomposed by 

 sulphurous acid. Yet it is well known that nitric acid is 

 found — and on M.Gay-Lussac's theory ought to be found— in 

 the house-acid. This is, however, accidental ; it may be always 

 prevented. It requires time only to effect the total decom- 

 position of all the nitric acid ; — by time, I mean, continuing the 

 process so long that sulphurous acid shall be constantly pre- 

 sent in the house, and that the gravity of the house-acid be 

 not too low. If the gravity is low, the nitric acid formed will 

 of course be very weak : it is then to be determined whether 

 sulphurous acid gas will decompose this weak nitric acid. I 

 distilled \ ounce pf nitrate of potash with jounce of oil of vitriol, 

 sp. gr. 1*84, diluted with its bulk of water. The acid vapours 

 were received into 2\ ounces of water. The acidulated 

 water acted rapidly on copper ; a current of sulphurous acid 

 gas was passed through it; a few bubbles of gas escaped, pro- 

 bably deutoxide of azote. The liquid was saturated with sul- 

 phurous gas: it then acted not upon copper; a small portion 

 of oil of vitriol, sp. gr. 1*84, was added to it; violent efferves- 

 cence occurred, sulphurous acid gas escaped, followed imme- 

 diately by red nitrous vapour. The liquid changed to a deep 

 yellow colour, and acted rapidly on copper. The nitric acid 

 therefore was not decomposed in this case till the added oil of 

 vitriol had abstracted a portion of water, — an effect equivalent 

 to the concentration of the nitric acid. The experiment was re- 

 peated, using undiluted oil of vitriol. The gas from 1 ounce of 

 nitre, \ ounce of oil of vitriol, sp. gr. 1'84, was received into 4 

 ounces of water; the gravity became 1*036, and the liquid was 

 slightly tinged yellow. Sulphurous acid gas was passed through 

 it, and a brisk effervescence took place ; deutoxide of azote was 

 evolved; the yellow tinge disappeared. The effervescence ceased 

 in about four hours. The liquid was saturated with sulphurous 

 gas; its gravity became 1*060. The apparatus stood some days ; 

 sulphurous gas was repeatedly passed through the liquid at diffe- 

 rent temperatures, from 32° to 212° Fahr. It had the same cha- 

 racter with copper as above stated : a portion of the liquid, 

 mixed with pure muriatic acid, rapidly dissolved gold; the 

 nitric acid was therefore undecomposed. Common aqua fortis, 

 diluted to sp. gr. 1*08, treated as above with sulphurous acid, 

 was not decomposed. 



The effervescence observed in these experiments is owing 

 to the decomposition of nitious acid ; for if the liquid is boiled, 

 red nitrous vapour escapes, and sulphurous acid no longer 

 causes any effervescence. It is deutoxide of azote only which 



