VOL. LXXII.J PHILOSOPHICAL TRANSACTIONS. 2g3 



g. The edulcorated powder (e) was now perfectly white; was not acted on 

 either by the vitriolic, nitrous, or marine acids, but readily melted into a glass 

 with fossile fixed alkali; during the melting an effervescence took, place. 



h. The white powder (p) readily dissolved in diluted vitriolic acid, and 

 under a slow evaporation formed crystals which had the appearance and the taste 

 of alum. These crystals were then reduced to powder, and boiled in alcohol. 

 The alcohol was decanted off, but did not appear to have dissolved any part of 

 the powder; nor did it afford any precipitate on the addition of mild fixed alkali. 



Conclusions. — From these experiments it appears, that the Rowley-rag-stone 

 consists of siliceous earth, clay, or earth of alum, and calx of iron. From the 

 latter must be deducted 1 \\ for the quantity of calciform iron, found by experi- 

 ment to be contained in the quantity of phlogisticated alkali made use of, and 

 then the proportions in 100 parts of the stone will be these: Pure siliceous 

 earth A7±; pure clay, free from fixable air, 324-; iron in a calciform state 20; 

 the sum 100. 



From this view of the component parts of this stone, it is not improbable, 

 that it might advantageously be used as a flux for calcareous iron ores. The 

 makers of iron are acquainted with such ores; but never could work them to 

 advantage, for want of a cheap and efficacious flux. 



Toad-Stone, 



From Derbyshire; sent to Dr. W. by Mr. Whitehurst, who has so fully and 

 so accurately described the mode of its stratification, that it is needless to enlarge 

 on that subject. 



More obvious properties. — Of a dark brownish grey, a granulated texture; 

 with several cavities filled with crystallized spar. It does not strike fire with 

 steel. It melts to a black glass. 



Exb. A. 100 parts rubbed to an extremely fine powder in a China mortar, 



and boiled in marine acid; the solution was decanted: the undissolved part, after 

 proper washing and drying, weighed 7 1 • 



b. The undissolved part was rubbed with twice its weight of mild fossil alkali, 

 and then exposed to a red heat in a black lead crucible for 1 hour. 



c. This mixed mass was reduced to powder, and repeatedly boiled, first in 

 marine afterwards in strong vitriolic acid: the residuum now weighed 56, and 

 was perfectly white. 



D. The liquors of exp. a. and c. being put all together, phlogisticated fixed 

 alkali was added till no further precipitation ensued. This precipitate was a 

 Prussian blue, which, when washed and dried, weighed 56-V- After exposure 

 to a red heat in a crucible for 40 minutes, it weighed only 2Q, and was wholly 

 attracted by the magnet. Now the 2 oz. 5 dr. and 32 gr. of phlogisticated fixed 

 alkali used in this experiment, contain 13 gr. of calciform iron, as ascertained by 



