550 PHILOSOPHICAL TRANSACTIONS. [ANNO 1784. 



changed ; for it did not dissolve in nitrous or marine acids, but wholly dissolved 

 in the greatly concentrated and boiling vitriolic acid, from which it was again 

 separated by the addition of water, (c 2.) 



g. The solution d was saturated with distilled vinegar, and then evaporated to 

 dryness, but with less than a boiling heat. The sal diureticus, thus formed, 

 was washed away with alcohol. The remaining salt weighed 5 drs. nearly. 2. 

 This salt had the appearance and the taste of vitriolated tartar; it decrepitated 

 in the fire ; roasted with charcoal-dust, it formed a hepar sulphuris ; and with 

 muria calcarea gave a precipitation of selenite. 



h. The salt formed with the nitrous acid e shot readily into beautiful perma- 

 nent crystals, of a rough bitterish taste. 2. Some of this salt was deflagrated 

 with nitre and charcoal, and the alkali afterwards washed away. 3. The resi- 

 duum, being the earth of the marmor metallicum, was very white, burnt to 

 lime, and again formed an insoluble compound with acid of vitriol. 



i. 100 grs. of terra ponderosa ae rata were dissolved in diluted marine acid. 

 Vitriolic acid was dropped into this solution, till no more precipitation ensued. 

 The precipitate, after very careful washing and drying, was exposed to a red 

 heat in a covered tobacco-pipe for half an hour : when cool, it weighed 1 17 grs. 

 2. 50 grs. of terra ponderosa ae rata in a lump were put into diluted vitriolic 

 acid ; but the action of the acid on it was hardly sensible ; even when made hot. 

 Marine acid was then added, and after some time an effervescence appeared. The 

 terra ponderosa vitriolata, thus formed, after proper washing and drying, was 

 exposed to a red heat for an hour : it then weighed 58.4 grs. 



Conclusions. — 1st, It appears that the marmor metallicum is composed of 

 vitriolic acid and terra ponderosa, D, e, f, g, h. 2dly, That this compound, 

 though probably soluble in water, has so little solubility as almost to escape de- 

 tection by the nicest chemical tests, B 1, 2, 3. 3dly, That it is not soluble in 

 acids of the usual strength ; but that it perfectly and entirely dissolves in highly 

 concentrated vitriolic acid, from which it again separates entire and unchanged 

 on the affusion of water, c 1, 2. 4thly, That it cannot be decomposed (via 

 humida) by mild fixed alkali, c 4. Sthly, That it may be decomposed (via 

 sicca) by the vegetable fixed alkali, d, e, g, h. 6thly, That it may be decom- 

 posed by inflammable matter, uniting to its acid, and forming sulphur ; but that 

 it cannot be decomposed by heat alone, a 1. 7thly, From experiments i J, 2, 

 it appears that 100 parts of this substance contain, of vitriolic acid pure 32.8, 

 terra ponderosa pure 67.2. For the 100 parts of terra ponderosa aerata, used 

 in the experiment 1 1, would lose during the solution 20.8 of fixed air {^ 1st, a;) 

 then, deducting 0.6 for the marmor metallicum contained in the terra ponderosa 

 aerata (§ 1 st a 1, 2,) there remains 78.6 of pure terra ponderosa. This, when 

 saturated with vitriolic acid, and made perfectly dry, weighed 117 ; consequently 

 it had taken 38.4 of vitriolic acid. 



