76 Essay on the Transition Rocks of the Caiaraqui. 



This curious substance appears to me, very decidedly, to be an in- 

 filtration, as the cup-shaped ends are invariably present, either as a 

 whole or in part, and are uniformly thicker by many lines than the 

 vertical portions, whilst the bottom of the cup is again thicker than 

 its own sides, which also gradually thicken as they curve down. 



In the denuded masses of the limestone it is much more easily ex- 

 tracted than in those which have not been long exposed to the action 

 of the atmosphere, and the upper surface of the hmestone has then 



The skeleton, after being left twelve hours, suffered no alteration. It was then put 

 into a strong solution of prussiate of potassa, but no variation took place ; the solution 

 remaining colorless. 



It was now removed into a glass mortar, with a small portion of water, and on 

 slightly pressing it, it gave way and Was with very little trouble pounded into a 

 brown muddy mass, resembling clay. Upon this mud, the solution of prussiate of 

 potassa was poured, when the usual indication of tritoxide of iron was observed. 



When the precipitation had fully taken place, the solution was decanted and nitric 

 acid poured over the precipitate, but no change nor anj^ developement of lime took 

 place until the prussiate of potassa was again admitted and the vessel slightly shaken, 

 when the whole solution turned of a lively greenish blue, and in a few hours a co- 

 pious dark blue precipitate occupied the bottom of the glass. 



A little of the last nitric acid had been decanted off previously to the last experi- 

 ment, but after it had remained for some hours at rest and muriate of soda vi^as drop- 

 ped into it, nothing occurred 5 the muriate subsiding in its proper form and remain- 

 hig undisturbed. 



In muriatic acid, both dilute and pure, the adhering limestone dissolved very slow- 

 ly and with much less effervescence than in the nitric, but a copious deposit occu- 

 pied the bottom of the vessel, which after twenty four hours was converted into a 

 whitish jelly like substance, resembling borax when deprived of its water of crystal- 

 lization. The mineral itself remained unchanged, although it required several fresh 

 accessions of the acid to free it from its adhering lime and other foreign substances. 

 After a few days standing, the borax-like clouds were gradually resolved into a 

 browner white gelatinous mass, which sank to the bottom of the vessel. Taking up 

 a portion of this substance accidentally, on a glass stirring rod, and holding it to the 

 blue flame of a candle at the bottom, it bubbled violently, and communicating a 

 vivid rose red light, (probably from the presence of the acid,) to the flame, it soon 

 dried into a hard white coating on the glass, which required some trouble to remove. 



For want of time and materials I could not continue the application of chemical 

 tests, but at leisure intervals I subjected it to other analyses. 



Before the blowpipe, on charcoal, there was no decrepitation ; nor per se in for- 

 ceps exposed ; nor enclosed in the platinum forceps, \yith borax, on charcoal, it 

 fused readily. With borax, on P. W. fusion easy ; when cool, colorless glass. 

 With salt of phosphorus, more difficult of fusion, but at length dissolved, and on 

 cooling exhibited an opaline glass, vsnih large flaws. 



Its specific gravity is 2.5, or the same as the investing or invested limestone. 



It has scarcely any action with the electrometer, although every precaution was 

 used ; its electricity, therefore, is feeble. 



Magnetism, by the usual modes, shewed no action, or at least very feeble if any. 



Phosphorescence — none apparent, in any way. 



