On the Chemical Covtposition of Clay-slate. 257 



Analysis of Clay-sJate, hy separation into its component portions 

 {Gemengtheile). 



The clay-slate, reduced to fine powder, was several times 

 digested with moderately concentrated muriatic acid, and the 

 solution filtered ; and, in order to sepai'ate the silica of the por- 

 tion decomposable in acids from the undecomposable component 

 part, the still moist filter with the residue was then boiled with 

 a concentrated solution of carbonate of soda in a platinum ves- 

 sel, and the liquid obtained was filtered while hot. The re- 

 mainder, which had the same colour as clay-slate, became white 

 when exposed to a high temperature, a sufficient proof that the 

 colour of the clay-slate proceeded from a mixture of an organic 

 substance, and that this colouring matter is contained only in 

 the portion undecomposable by acids. After the powder was 

 exposed to a red heat it was Aveighed, and from its weight was 

 calculated the weight of the part undecomposable by muriatic 

 acid. The alkaline solution, separated by filtration from the in- 

 soluble powder, was saturated to excess with muriatic acid, then 

 evaporated to perfect dryness, and the silica, as above, separated 

 from the dry mass by dissolving the latter in water. The solu- 

 tion obtained by digesting the powdered clay-slate with muriatic 

 acid, was tested for copper by means of sulphuretted hydrogen, 

 but no precipitate appeared. Alumina and oxide of iron were 

 thrown down by ammonia, and separated, as in the previous 

 analysis. The portion of magnesia still contained in the solu- 

 tion, separated by filtration from the succinate of iron, was preci- 

 pitated by phosphate of soda. The lime was, as formerly, pre- 

 cipitated from the solution filtered from the oxide of iron and 

 alumina. In order to determine the magnesia and the alkali in 

 the solution separated from the lime, the liquid was evaporated 

 to dryness, and for a long time cautiously heated in a weighed pla- 

 tinum crucible until all the sal-ammoniac was volatilized. There 

 remained behind chloride of magnesium and chloride of calcium, 

 which were converted into sulphuric salts by sulphuric acid. 

 The salts were then weighed and dissolved, the sulphuric acid 

 was precipitated by acetate of baryta, the solution evaporated to 

 dryness, and the dry mass heated to redness in a platinum ves- 

 sel. The heated mass, which consisted of carbonates, was treat- 



