190 



FILTERING STONE. 



gas. A hundred parts of the ochre freed from lead were 



reduced to eighty-eight of a pretty fine red powder. The 



product was pure water. 

 Muriatic acid Muriatic acid applied to the residuum, separated forty- 

 separated -44 f our p ar ts of sand : consequently there were forty-four parts 

 of sand. „ . , ... 



ox red oxide likewise, 



Hidrate of red If forty-four parts of this oxide were combined with twelve 

 ojdde. f water, one hundred parts must have been united with 



twenty-seven in this oxide. It was therefore a hidrate, with 

 base of red oxide. 



If the red oxide, which is generally less disposed to enter 



into combination, be capable of producing a hidrate, must 



not the black oxide be much more so ? The hidrate of i on 



then with base of oxide at a minimum will be found some 



Hidrate of day, either pure, or in a compound of this metal. I am of 



carbon^oV" 1 P m * oa xt is m tms state > tnat it; makes a P art of ti ie cal '- 

 iioru bonate of iron, the base of which is always at a minimum. 



IX. 



On Filtering Stones, and the Method of determining the spe- 

 cif c Gravity of Substances with large Pores. By Mr. 



GUYTON *, 



Filtering JD>0TH Linneus and Wallerius have spoken of a filtering 



stones suppos- sandstone: cos Ultrum particulis arenaceis ceqvalibus, aquam 

 ed to be arena- . J J . x M 



ceous. transmittcndo stdlans : cos particulis arenaceis puris aquam 



transmittals. On their authority most mineralogists have 

 classed these stones among the varieties of arenaceous quartz : 

 but we do not find, that they had ascertained whether the 

 silex in them were pure, or merely the predominant princi- 

 ple. The former appears however to be the most general 

 Kirwan men- opinion, since, excepting one passage in Kirwan, where he 



tions one part- men tions the picrrc de Hats amono- the silicicalcareous stones 

 ly calcareous. * ■ , ,° 



as porous, and used lor filtering y, we do not find in the 



* Annales de Chimie, Vol. LX, p 121. Nov. 18G6. 

 •J- Elements of Mineralogy, Vol. I. p. 102. 



