On the Chemical Composition of Clay-slate. S55 



1. Of a thin lamellar clay- slate, by D'Aubuisson. 



2. Of the clay-slate of Dunmeniss in Downshire, by Stokes. 



3. Of the clay-slate of Gaggenau in Baden, by HoUzmann. 



4. Of the clay-slate of Kieiderselters in Nassau, by Wirapf, 



(»•) (20 (3.) (4.) 



S'l'ca, 48.6 09.4 C4.34 79 17 



^'"™'"^' 23.5 17.4 23.90 10^42 



Oxide of iron, .... 11. 3 11.6 9.70 6.27 



Oxide of Manganese, . 0.5 . 



Lime, , 2.1 



Magnesia, 1.6 00 



Potash, 47 ' 



Carbon, .._.... o.3 '^^ 



Sulphur 0.1 



"^^'ale'"' 7.6 6.4 2.22 ~T8 



»8-2 09.1 100.16 9"a64 



All these analyses, as it appears, are of varieties of clay-slate 

 occurring in the transition series of rocks ; and the small agree- 

 ment among them, renders it probable that clay-slate is not a 

 simple mineral like mica, as has often been considered the case, 

 owing to its supposed passage into mica-slate, but rather that it 

 constitutes a very finely mixed, only apparently homogeneous 

 niountam-rock. I have, therefore, made some analyses to ascer- 

 tarn if clay-slate can be separated by treatment with acids into 

 a decomposable and an undecomposable component ingredient 

 just as C. Gmelin has shewn to be the fact with phonSite and 

 basalt, and Berzelius with meteoric stones ; and as I have fully 

 succeeded in this attempt, I have performed complete analyses 

 of several varieties of clay-slate. 



Each clay-slate was examined in a double manner ; first by 

 separating its two component portions by means of muriatic acid 

 and then submitting each portion separately to analysis • and' 

 secondly, by treating and analyzing the substance as a whole' 

 when of course the result ought to correspond with that of the 

 combmed processes in the first analysis. 



I shall begin by describing the method employed in the last 

 kmd of analysis, as it required the separation of the whole con- 

 stituent parts of the clay-slate ; and I shall afterwards point out 

 in what respect the first ditFercd from it. 



This slate is employed for paving the streets of Paris._E 



DIT. 



