256 On the Chemical Composition of Clay-slate. 



Analysis of Clay-slate considered as a whole. 

 The clay-slate was decomposed by fusion with carbonate of 

 potash, the melted mass was digested with diluted muriatic acid, 

 and the solution evaporated to perfect dryness. The silica \vas 

 separated in the usual v/ay from the dry mass. A stream of sul- 

 phuretted hydrogen was passed through the liquid, which had 

 been separated by filtration from the silica ; and a very incon- 

 siderable precipitate of sulphuret of copper was thus formed, 

 which, as the quantity was too small, was only dried, very 

 strongly heated, and determined as oxide of copper ; while in 

 the filtered solution the oxide of iron was converted into the 

 peroxide by nitric acid. The alumina and oxide of iron were 

 precipitated by ammonia, then dissolved in muriatic acid, and 

 separated by means of caustic potash. The alkaline solution was 

 acidulated, and the alumina precipitated by ammonia. The 

 oxide of iron not having been dissolved by the caustic alkali, was 

 dissolved in muriatic acid, and precipitated by succinate of am- 

 monia. The succinate of iron was heated, and the iron deter- 

 mined as peroxide. The liquid separated by filtration from the 

 succinate of iron, and which contained a minute quantity of 

 magnesia, was added to the liquid containing magnesia that I 

 obtained after the separation of the lime. The lime was sepa- 

 rated by oxalate of ammonia, from the solution which I obtain- 

 ed after the precipitation of the alumina and oxide of iron by 

 ammonia ; and the oxalate of lime was exposed to a red heat, 

 and thus converted into carbonate of lime. The magnesia was 

 jDrecipitated by phosphate of soda. The alkali could not be de- 

 termined in these analyses. The quantity of water was ascer- 

 tained bv the loss sustained during heating. As, however, it 

 appeared during the solution of the clay-slate in acid, that it 

 contained a minute portion of carbonate of lime, the carbonic 

 acid was also included in this loss of weight ; but the quantity 

 was determined in the second analysis, and the amount of water 

 was corrected. The quantity of carbon, a substance v/hich is 

 contained in all the clay-slates I have examined, could not be as- 

 certained, but it was, as we shall afterwards sec, included in the 

 calculation of loss. After a long continued strong red heat the 

 dark colour of the clay-slate remained unchanged. 



