114 



iiCTION Oy HEAT MO-DIFIEIT 



in order to maintain this part of the Huttonian Theory, 

 was nevertheless gained. For granting that our carbonates- 

 were impure, and that their impurity rendered them fusible,, 

 still the same is true of almost every natural carbonate ; so 

 that our experiments were, in that respect,' conformable to na- 

 ture. And as to- the other surmise, it has been shewn by 

 compariiig together a varied series of experiments^ that the 

 mutual action between the lime afid the porcelain was oc- 

 casioned entirely by the presence of the carbonic acid,, si nee, 

 when it was absent,.no action of tliis kind took place. The 

 fusion of onr carbonates cannot, therefore, be ascribed to the 

 porcelain, 

 Exprj.rafiits Being convinced, however, by many observations, that the 



ptoj, cted to fusibility of the carbonate did not depend upon impurity, 

 det.rmine this ^ ,^ « *< , • t^ ■>-' 



pomt. I have exerted myself to remove, oy fresh expermnents, every 



doabt that has arisen on the subject. In order to guard 



against natural impurities, I have applied to such of my friends 



as have turned their attention to chemieal analysis, (a branch 



of the science to Vv^hich I have never attended, (to furnish 



me with carbonate of lime of undoubted purity). Toobviatg 



the contamination arising from the contact of the porcelain 



tubes, I determined to confine the subject of experiment in 



some substance which had no disposition to unite with the 



carbonate, I first tried charcoal, but found it very troublesome, 



ov/ing to its irregvilar absorption of water and air. 



Vine carbonate I then turned my thoughts to the construction of tubes or 



pktiiiaroHed *^"P^ °^ platina for that purpose. Being unable readily to 



up. procure proper iiolid vessels of this substance, I made use of 



thin Laminated plates, formed into cups. My first method' 



was to fold the plate exactly as we do blotting-paper to form 



a filter (Fig. 26. See the quarto Plate marked 3, in vol. xiir.)-; 



this produced a cup capable of holding the thinest liquid ; 



and being covered with a lid, formed of a similar thin plate, 



bent at the edges, so as to overlap considerably (Fig. 28.), 



the carbonate it contained was secured on all sides from the 



contact of the porcelain tube within which it was placed. 



Another convenient device likewise occurred :. I wrapt a 



piece of the plate of platina rounci a cylinder, so as to form 



a tube, each end of which was closed by a cover like that just 



described (Fig. 27. and2p.). In figure 26". and 27.. these 



cups are represented upon a large scale, and in 28. and 2.9. 



nearly 



