Mr. KirwarCs Ucfuiat'ion of the Ihdton'ian Theory, 9 



in aqua detcrtninatas acqitirunt formas, veruin cluim ni fallor 

 fatis attenuatu." Ecrnman, ii, p. 15. It is fufHcicnt that the 

 panicles fufpendcd and lufiiciently attenuated l)ave an afiinity 

 to each other. 



Page 22, <' Barytic earth 15 well known to have a Wronger 

 attraction to fixed air than common calcareous earth has, fo 

 that the carbonate of barytes is able to endure a great degree 

 of heat before its fixed air is expelled : aceordinglv, when cx- 

 pofed to an increafing heat at a certain temperature, it is- 

 brought into fufion, the fixed air I'till remaining united to it: 

 it the heat be further increafed the air is driven off, and the 

 earth lofes its fiuidity." And, p. jS.5, " Carrara marble may 

 require a heat of 6300° of Wedgwood to melt it in the opeii 

 air; but under fuch a prelTure as would retain this gas it 

 cannot be inferred that it might not melt with the heat of ci 

 glafshoufe furnace. In like manner it may be true that 280 

 cubic inches of air acting on charcoal cannot cfTccl the fufiou 

 of one grain of this marble after its fixed air is driven oiV 

 from it; but we cannot from thence draw any inference ap- 

 plicable to a cafe where the carbonic acid is retained, and 

 where the aftion of heat is independent of atmofpheric air." 

 Now, in no experiment with which I am acquainted has na- 

 tive aerated barytes been fufcd without the expulfion of its 

 air, or union with the earth of the crucible. Dr. Hope, in- 

 deed, fufed it in a black lead crucible, but found it loll 23 per 

 cent, nearly of its weight; which is the whole, or nearly fo, 

 ol the air contained, and accordingly it made but a verv (ligiit 

 effervefcence with marine acid. Hence the pofitlon laid 

 down, p. 23, that barolite or native carbonate of barytes 

 may be fufed and ftill retain its fixed air, is founded on no 

 experiment; but from all known experiments the contrary 

 inference is fairly deducible with rcfpedl to it, as well as with 

 refpcdt to Carrara marble; nor is there any reafon to think 

 tiiat a lower heat, independent of the atmofphcrc, could have 

 any other effect. 



Page 201 — 203. The fact alluded to, namely, that fliells 

 are found incorporated in the body of a rock at a great height 

 near Guancavelica, I have fully fiated and explaitied in a dif- 

 fcrlalion long fiuec printed, and which' accompanies this 

 letter; lo which I (hall therefore beg leave to refer*. 



I'age 24A- " Mr. Kirwan, in order to account for the 

 ina(jnilude of mallls of iron found in Siberia and I\tu, fup- 

 po'es that Iniall pieces of native iron have bn-n oriiiinally 

 agglutinated by petrol : this is, no doubt, the mod fingular 

 of all the opinions advanced on the fubje6l; and, as it bor- 

 • Set ttie next i«rticlc in tht jt)rcftnt Nunibci.— l^iuir. 



rows 



