'294 PHILOSOPHICAL TRANSACTIONS. [ANNO 1/82. 



a separate trial ; therefore, deducting 13 from 22, we have 1 6 for the quantity of 

 calciform iron obtained from the stone. 



e. The earthy parts were next precipitated from the liquors by the addition of 

 mild fossil alkali. The precipitate, when perfectly edulcorated and dried, weighed 



29tV 



f. Distilled vinegar was added to this powder, and suffered to stand in a cool 



place for 4 hours; the vinegar was poured off, and the residuum repeatedly 

 washed with pure water. To these liquors mild fixed alkali was added, and a 

 white precipitate subsided, which, when washed and dried, weighed 7-^. 



g To the residuum (f) dilute vitriolic acid was added: a solution took place, 

 which solution, by evaporation and crystallization, yielded alum. 



h. The part of the residuum (f) undissolved by the vitriolic acid was boiled in 

 nitrous acid, in marine acid, and in aqua regia, without being diminished; the 

 weight of it when dried was 7-rV It could not be fused by the greater heat of 

 a blow-pipe, but melted into a glass when mixed with calcareous earth. 



i. The undissolved part (exp. c.) was not fusible by itself; nor was it acted on 

 by vitriolic, nitrous, or marine acid. It melted into a glass with fossil alkali. 



k. The precipitate of 7 T v (exp. p.) after a sufficient exposure to heat was put 

 into 1 oz. of water: the next morning the water had a pellicle on its surface, and 

 tasted like lime-water. 



c. Siliceous earth 56 ? .-., 5 



ii . More ditto 7 T » ff ( — "»» 



^ , . TT .1 , , __ d. Calciform iron \6 



Conclusions. — Hence it appears, that 100 F K calcareous earth.. . 



parts of this specimen of toad-stone contained: <*■ h. Earth of alum 14- 



I o 



i 



io'A 



From the addition of \-fc of weight it is probable, that the substances capable of 

 uniting with fixnble air were not in the specimen used fully saturated with it, as 

 they would be after their precipitation by the mild alkali. On repeating these 

 experiments with different portions of the toad-stone, the quantities of the 

 calcareous earth were found to differ a little; but nothing further appeared to 

 invalidate the general conclusions. 



