46 Olservaiivis on the Change of 



It is therefore very different from the schirUus, the com- 

 ponent ingredients of which were ascertamed by the follow- 

 ing analysis. 



Analysis of t/w Schistus from Iceland'^. 



A. 250 grain?, by distillation, yielded water, which, in 

 the latter part of the process, became slightly acid and 

 turbid, = 4C.50 grains. 



E. The heat was gradually increased, nntil the bulb of 

 the retort was completely red hot. During the increase of 

 the heat, a thick brown oily bitinncn came over, which 

 weiirheJ 7.50 grains ; it was attended with a copious pro- 

 duction of hvdrogen, carbonated hydrogen, and carbonic 

 acid, the whole of which may be ectmiated at 23.75 

 grains. 



C. The residuum was black, like charcoal, and weighed 

 170.25 grains ; but, being exposed to a strong red heat in 

 a crucible of platina, it burned with a faint lambent flame, 

 and was at length reduced to a pale brown earthy powder, 

 which weighed 122 grains ; so that 54.25 grains were 

 consumed. 



D. The 122 grains were mixed with 240 of pure potash ; 

 and, as some particles of charcoal remainea, 50 grains of 

 nitre were added, and the v.'hole was strongly heated, 

 durina; half an hour, in a silver crucible. The mass was 

 then dissolved in distilled water ; and muriatic acid being 

 added to excess, the liquor was evaporated to dryness, ancf 

 was again digested with muriatic acid much diluted ; a 

 quantity of pure silica then remained, which, after having 

 been exposed to a red heat, weighed 98 grains. 



E. The liquor from which the silica had been separated 

 was evaporated nearly to dryness, and added to boiling lixi- 

 vium of potash ; after the boiling had been continued for 

 about one hour, the liquor was filtrated, and a (]uantity of 

 oxide of iron was collected, which amounted to 6 grains. 



F. Solution of muriate of ammonia was added to the 

 preceding filtrated liquor ; and the whole being then heated, 

 a copious precipitate of alumina was obtained, which, after 

 having been made red hot, weighed 15 grains. 



Carbonate ( f soda caused the preceding liquor (after the 

 separation of alumina) to become slightly turbid, but not 

 any precipitate could be collected. 



• The remtiining specimens are now in the British Museum, and in 

 the coU-jciign of the Riijht Honourable Charles Grcrillc. 



By 



