On the Cheinical Composition of Clay-slate. 261 



I made some experiments to ascertain if the relation of the 

 component part decomposable by oxides, to that of the part un- 

 decoraposable, be the same in every spacimen of clay-slate, and 

 I obtained the following results. 



Goslar. Lehsten. 



30.53 : G9.47 25.31 : 74.69 



29.73 : 70.27 24.48 : 75.52 



28.98 : 71.02 23.G1 : 76-39 



In all these analyses the iron was regarded as the peroxide. I 

 ascertained by direct experiment in the case of the portion decom- 

 posable by acids, that the iron is contained in it only in the state 

 of peroxide. To determine this the clay-slate was dissolved by 

 muriatic acid in a small flask, which was closed by a tightly fit- 

 ting glass-stopper. The solution diluted with water yielded with 

 cau.stic potash the usual brown precipitate of oxide of iron. This 

 point could not be determined by exact experiment in the por- 

 tion indecomposable by acids ; but it is probable that the iron 

 is there also in the state of peroxide. 



It results from these analyses, that the transition clay-slate, from 

 the great formation constituting the Rhenish slate series, the transi- 

 tion-rocks of the Hartz, and those of Thuringia, and indeed most 

 probably all transition clay-slate, can be separated by treatment 

 with acids, into two, and if the small admixture of carbonate of 

 lime be taken into account, into three component ingredients. The 

 composition of the first-mentioned two portions is not similar, but 

 the chemical constituents are the same, though extremely different 

 in their relative proportions. We have also found that the pro- 

 portion of the part decomposable in acids, to that of the portion 

 indecomposable, is not the same in true varieties of clay-slate 

 which were examined ; and, indeed, not even in the different 

 fragments of one and the same variety, though the differences 

 are not very great. But the distinctions are sufficiently great 

 to enable us to ascertain, with some probability, if the quan- 

 tities of oxygen of the separate chemical constituents of the 

 clay-slate stood in a simple relation. On comparing, however, 

 tlie numbers placed next the results of the analysis, with the 

 amount of oxygen in the ascertained chemical constituents, we do 

 not find this to be the case. It is when we consider the com- 

 position of the clay-slate as a whole, that we have the nearest 



s2 



