352 On the Composition and Origin of Porcelain Earth. 



series, not only in Cornwall, but also in the Alps and in the 

 Vosges, and are situated under precisely the same circum- 

 stances, the fact that the one is decomposed to a hundred times 

 the extent of the other would alone point at a difference in 

 the composition of the felspar of the respective rocks. This 

 is now, in some measure, established by the foregoing analyses 

 of kaolin. It is, however, desirable that the felspar of the pro- 

 togine should also be examined, though it will not be easy to 

 procure a proper specimen for this purpose ; and the chemist 

 must be cautious in his selection of one, that he does not take 

 it from the micaceous or shorlaceous granites with which the 

 protogine is associated. 



We have yet so much to learn concerning the properties of 

 alumina and its combinations, that it is difficult to give a satis- 

 factory account of the changes which occur even during the 

 decomposition of common felspar. It is generally supposed 

 that the alkali is first set at liberty and then acts on the nascent 

 silica; but why not also on the alumina whilst in the same 

 condition, or on the silicate of alumina, and still more on the 

 alkalino-silicate of alumina, which is very soluble in alkalis 

 and is most probably present in disintegrating felspar ? 



But supposing these difficulties surmounted, we have still 

 the first and fundamental change to account for, viz. the sub- 

 version of the powerful affinity by which the constituents of 

 the felspar are united. It is an easy matter to say that it is ef- 

 fected by the long-continued action of water and carbonic 

 acid, but what is the modus operandi! In the laboratory, 

 we cannot dissever the component molecules of this mineral 

 by the most powerful acids ; how then can the weakest effect 

 it in Nature ? 



Berzelius has made some excellent observations on this sub- 

 ject, (Traite de Chimie, tom. iv. p. 574<,) instancing other sub- 

 stances, both natural and artificial,which resist solution in acids, 

 contrary to what might be inferred from the nature of their 

 composition ; and he concludes that the elements of compound 

 bodies do, in reality, combine in two distinct states of union. 



Fournet, who has paid great attention to the difficult sub- 

 ject under consideration, is of opinion that the felspar must 

 be first disintegrated (desagrege) before the chemical action 

 can commence; and he conceives that this is actually accom- 

 plished in consequence of felspar possessing the property of 

 dimorphism, the new or second arrangement of the particles 

 causing the disintegration. Becquerel justly remarks on this 

 solution, that we have yet to learn that the particles of igneous 

 rocks, on consolidation, did not assume a permanent form ; 

 and that they have experienced by the lapse of time a change 



