Page:Transactions of the Geological Society, 1st series, vol. 4.djvu/442

From Wikisource
Jump to navigation Jump to search
This page has been proofread, but needs to be validated.

1. One hundred grains being placed upon red hot iron for the expulsion of the water of absorption, were thereby diminished of a grain.

2. The remainder being reduced to powder in a porcelain mortar and exposed to diluted muriatic acid until all effervescence ceased, there remained an insoluble residue of the original dark colour of the limestone, which when carefully washed and dried, weighed 10 grains; allowing therefore for the weight of the carbonic acid and lime, after the expulsion of the water of absorption, 89 grains.

3. The supernatant acid used in this experiment being decanted, and neutralized by the addition of an alkali, yielded no precipitate of iron to the tincture of galls; but the prussiate of potass threw down a blue precipitate upon which however no reliance can be placed; as it is well known that the prussiate of potass is not a satisfactory test of the presence of iron when this metal exists in an inconsiderable portion.

4. The ten grains of dark brown powder mentioned in No. 2, being collected, washed and dried, were exposed to the heat of a flame of a candle urged by the common blow-pipe, when combustion instantly ensued, accompanied by a lambent flame, which continued during some seconds, the powder thereby losing its colour and becoming white; attended also by a loss of weight, amounting to of a grain. Hence it is manifest that the colour is owing to bitumen.

5. To ascertain the proportion of alumine (which from its chemical combination with silex remained insoluble in the muriatic acid) a plan recommended by Mr. Holme was adopted. One hundred other grains of the same limestone were calcined in a platinum crucible, and the loss of weight owing to the expulsion of the carbonic acid was found to equal 40 grains.