4C8 Exain'matioji cf iht. fu/ible Etirth. 



•happen, tliougli the nitrous fpirit be previoudy mixed with cvcii a l^rgc quantity of water, 

 -providcU die quantity of fclution adiled to it does rot exceed that of the nitrous fpivit in the 

 mixture. Tlie appropriate nicnftruum for this fub(iance (that is, for keeping it in a (late of 

 dilute folution) appears, therefore, to be aqua regia ; and the due proportion of the two 

 acid's, of any piven ftrength, might be determined, if neccflary, with greater accuracy and 

 facility for this than for any other body I know of j becaufe, if there be even a very minute 

 furplus of marine acid in the folution, that furphis will inftantly betray itfelf, on dropping a 

 Jittlc into water; all that wasdiflblved by it, and no more, being precipitated by the water. 

 It may be obferved, however, that where an addition of nitrous acid is ufed, a faturated 

 folution cannot be obtained (unlefs by fubfcqucnt evaporation), the fame quantity of marine 

 acid being neceilary with as without that addition : the change or modification which the 

 nitrous acid produces in the marine, fervcs, in the prefent iiiftance, not for efFeding the 

 folution, as in the cafe of gold and fome other metals, but merely for en-ibling it to bear 

 ■water without depofiting its contents. 



Oil of vitriol dropped into the faturated marine folution, occafions no change till its quanr 

 tily comes to be about equal to that of the folution ; a coiifiderable efTcrvefcence and heat 

 are then produced, the liquor becomes millcy, and the marine acid is extricated in its ufual 

 vhite fumes. The mixture, heated nearly to boiling, becomes tranfparent, and afterwards 

 continues fo in tlie cold. This vitriolic folution is precipitated by water, and the preci- 

 pitate is redifiolved by marine acid. 



The faturated marine folution is indifpofed to cryftallife. By continued evaporation in 

 gentle heat it becomes thick and butyraceous, and in this (late it foon liquefies again on ex- 

 rofure tothe air. The butyraceous mafs, in colour whitifli or pale yellow, is not corrofive, 

 like the fimilar preparations made from fome metallic bodies, nor is it more pungent in tade, 

 but rather lefs fo, than the combination of the fame acid with calcareous earth. In a heat 

 incvea*cd nearly to ignition, the acid is dlfengagcd, and rifes in white fumes, which, received 

 in a cold phial, condenfe into colourlefs drops, without any appearance of fublimate. From 

 the remaining white mafs, fpirit of nitre extracts fo little as to exiiibit only a ilight milkinefs 

 on adding alkali ; a proof that nearly all the marine acid had been expelled ; for, while 

 that acid remains, the whole is diflbluble by the nitrous. 



The fubllanee in qucftion is not precipitated by PrufTian lixivium. A drop or two of the 

 lixivium do indeed occafion a little white or blueilh white precipitation in the faturated ma- 

 rine folution ; but in the more dilute no turbidnefs appears till the quantity of lixivium is fuch 

 as to produce that eflFedl by its mere water; and when the precipitate has at length been 

 formed, it rediiTolves in marine acid as eafily as that made by water; whereas the precipi- 

 tates refulting from the union of the PrulTian matter are not afled upon by acids till that 

 matter has been extradled from them by an alkali. For further fatisfaftion, in this im- 

 portant point, the experiment was repeated with a folution in aqua regia. Here the PruiTian 

 lixivium, in whatever quantity it was added, occafiontd no precipitation at all (only tlic 

 ufual blueifhnefs ariling from the iron always found inthe common acids); and pure aik.ali 

 added sfterwards precipitated the original white fubllanee unchanged. 



The following experiments of precipitation by alkalis were made with the marine folu- 

 tion before the eflecl of an addition of nitrous acid had been difcovcred ; and they were 

 made witli fo much care and attention, that it was not thought ncctflliry to repeat them 

 4. afterwards. 



