ino STONE CONTAINING POTASH. 



of ftones employed in the manufaftory of earthen-ware, a par- 

 ticularly exa6t anaiyfis was demanded of a flone, labelled grey 

 Cornijh *, in which I detected this alkali. I fhall not detain 

 you with a circumfrantial detail of my reiterated experiments, 

 which were undertaken with a view to learn the nature of the 

 flone under confideration, which is fought for by the potters 

 with avidity ; I fliall merely confine myfelf to point out its 

 chara<5lers, as well as that examination which may ferve to 

 eftabUfli the credit of my alTertion. 

 I am. Sir, with refped. 



Your moft obedient humble fervant, 



FREDERICK ACCUM. 

 Old Cowpton Street, Soho. 



Phi/fical CharaSiers vf a Siliceous Stone containing Potafh. 



Phyfical charac- THIS ftone is found in amorphous maffes, forming irregular 

 tcrspfaftone flrata, under the furface of a blue clay. Its colour, when 

 containing pot- ^ewly taken frOm the bed, is a greeniih-grey interfperfe.d with 

 black fpots ; but when left expofed to the air, it acquires an 

 sfli-grey colour. It is not very hard ; its powder is white. 

 When rubbed, it exhales a faint argillaceous odour. Its fub- 

 Itance is coarfe or uneven, having many fmall, fliarp, abrupt, 

 irregular elevations and irregularities. Its fracture is very ir- 

 regular. It may be eafily fcratched with a knife. It fcinti- 

 lates with fteel. It is abfolutely opaque in fmall fragments. 

 Urged before the blow-pipe, it froths and melts into a white 

 enamel. Treated with borax in a fimilar vvay, it forms a 

 reddifh bead. 



Its fpecific gravity is 2,465. 



ANALYSIS. 



Anaiyfis of a Experiment 1. — One hundred grains of the finely levigated 



itone containing ftone, after having been previoufly ignited f, were mixt with 

 potafli. ^ folutlon of potafti containing 400 grains of alkali, the mix- 



ture was evaporated in a filver capfcel to drynefs, transferred 



* I am not permitted to ftate the exa^t place in Cornwall where 

 this ftone is found. 



t 100 parts loft, during Ignition, 6 parts. 



into 



