different Earths for Carhon. 29 j 



contained in the chalk, which had also been thrown down 

 by the alkali. These glasses, compared with No. I, IV, 

 VI, X, XIV, and XVII, wherein the substances formerly 

 operated upon were fused per 5e,-exhibited a decided superi- 

 ority of purity and transparency. 



Experiment XX — Cornwall Clay Crucible. 



Pure lime - - - 20 grs» 



Lamp carbon 1 -80th, or - \ 



There resulted from the fusion of this mixture an elegant 

 primrose-coloured glass, of a different class as to depth of 

 water, if I am allowed the expression, delicacy of colour, 

 and real transparency, from any of the former. 



Experiment XXI — Cornwall Clay Crticille, 



Pure lime - - - 20 grs. 



Lamp carbon l-40th, equal to ^ 

 This mixture was fused into a fine yellow amber colour, 

 still retaining a decided superiority as to transparency and 

 lustre. It only differed from No. XX in the richness or 

 extra depth of the shade, which was intimately blended 

 with bright yellow and amber. 



Experimerit XXII — Cornwall Clay Crucible. 



Pure lime - - - 20 grs. 

 Lamp carbon - - 1 



A perfect glass was here also obtained, but all the fine 

 shades and tints of the two former experiments were lost. 

 The glass was of the same colour and class with Experi- 

 ments No. Ill, V, IX, XI, XII, XIII, and XVI, only pos- 

 sessed of a greater degree of transparency. One-fourth of a 

 grain of charcoal remained untaken up, and two very mi- 

 nute globules of iron of a silvery colour were visible. These 

 I estimated to weigh about the fifteenth part of a grain, and 

 infer that the precipitated lime now made use of contained 

 about l-300dth part its weight of iron. These experi- 

 ments were twice carefully repealed, with similar results. 

 Excepting once, in the experiment last noticed, the charcoal 

 had entirely disappeared. This I attributed to the crucible 

 remaining too long unopened after being taken from the 

 furnace, or to some unseen pore or crack. 



It would appear to result from the foregoing experiments, 

 that the combination of carbon with calcareous earth is ex- 

 tremely small, if not altogether doubtful. In all the sub- 

 stances submitted to experiment a portion of iron was con- 

 T 4 tained, 



