670 PHILOSOPHICAL TRANSACTIONS. [aNNO I79O. 



the quantity of nitrous acid exceeds, or at least does not fall much short of, that 

 of marine acid in the solution, the mixture suffers no precipitation from water. 

 Nor does any precipitation happen, though the nitrous spirit be previously mixed 

 with even a large quantity of water ; provided the quantity of solution added to it 

 does not exceed that of the nitrous spirit in the mixture. The appropriate men- 

 struum for this substance, that is for keeping it in a state of dilute solution, ap- 

 pears therefore to be aqua regia ; and the due proportions of the two acids, of any 

 given strength, might be determined, if necessary, with greater accuracy and faci- 

 lity for this than perhaps for any other body ; because, if there be even a very 

 minute surplus of marine acid in the solution, that surplus will instantly betray 

 itself on dropping a little into water, all that was dissolved by it, and no more, 

 being precipitated by the water. It may be observed however, that where an ad- 

 dition of nitrous acid is used, a saturated solution cannot be obtained, unless by 

 subsequent evaporation, the same quantity of marine acid being necessary with as 

 without that addition : the change, or modification, which the nitrous acid pro- 

 duces in the marine, serves, in the present instance, not for effecting the solu- 

 tion, as in the case of gold and some other metals, but merely for enabling it to 

 bear water without depositing its contents. 



Oil of vitriol, dropped into the saturated marine solution, occasions no change 

 till its quantity comes to be about equal to that of the solution ; a considerable 

 effervescence and heat are then produced, the liquor becomes milky, and the 

 marine acid is extricated in its usual white fumes. The mixture, heated nearly 

 to boiling, becomes transparent, and afterwards continues so in the cold. This 

 vitriolic solution is precipitated by water, and the precipitate is re-dissolved by 

 marine acid. The saturated marine solution is indisposed to crystallize. By con- 

 tinued evaporation in gentle heat, it becomes thick and butyraceous, and in this 

 state it soon liquefies again on exposure to the air. The butyraceous mass, in 

 colour whitish or pale yellow, is not corrosive, like the similar preparations made 

 from some metallic bodies ; nor is it more pungent in taste, but rather less so 

 than the combination of the same acid with calcareous earth. In a heat increased 

 nearly to ignition, the acid is disengaged, and rises in white fumes, which, re- 

 ceived in a cold phial, condense into colourless drops, without any appearance of 

 sublimate. From the remaining white mass, spirit of nitre extracts so little as to 

 exhibit only a slight milkiness on adding alkali ; a proof that nearly all the ma- 

 rine acid had been expelled ; for, while that acid remains, the whole is dissoluble 

 by the nitrous. 



The substance in question is not precipitated by Prussian lixivium. A drop or 

 two of the lixivium do indeed occasion a little white or bluish-white precipitation 

 in the saturated marine solution ; but in the more dilute no turbidness appears, 

 till the quantity of lixivium is such as to produce that effect by its mere water; 



