STONE CONTAINING POTASH. 127 



of the fluid they are made ufe of to ameliorate. In confe- Apparatus for 

 quence of which, they have been induced to apply their art to 

 the fimpleft method of affording an apparatus for the filtering 

 procefs, which (liall not be liable to ihefe objeftions. 



Plate VI. Fig. 1, reprefents the whole apparatus. Fig. 2 

 fiiews a fhaded fe6lion. A is a veflel of (lone-ware perforated 

 with holes, m, at bottom, upon which coarfe grave!, A, is 

 laid, and upon that a ilratum of fine gravel, and laftly fine 

 fand, g. Or otherwife, the bottom may be covered with a 

 coarfe cloth, which will renderthe graduated finenefs of the 

 gravel and fand lefs neceffary. Upon the top of the fand is 

 laid a perforated and loaded board or plate of earthen ware, to 

 prevent the fand from being difturbed when the water is poured 

 in. B is a lower veflel, into which the filtered water from A 

 drops, together with any fand that may efcape from above. 

 The clear water flows out through the neck a c into the veflTel 

 D for ufe. 



The ftru6lure, ufes, and effeds of this apparatus are fo ob- 

 vious, that it is needlefs to enlarge upon them. The finenefs 

 and depth of the; filiceous fand will regulate the perfeflion 

 and expedition of the procefs ; and the requifite cleannefs and 

 delicacy of the veflels and fand may be infured by changing 

 the latter from time to time; for example, once in a fortnight 

 or three weeks. W. N. 



XVIII. 



Examination of a Stone containing Potajh. Bj/ Frederic 

 Ac CUM, Teacher of P radical Cli€?nipy, PIiar?nacy, and 

 Mineralogy. 



To Mr. NICHOLSON. 

 SIR, 



blNCE Klaproth has detefled potafii in the lepldollte, introduftory 

 leucite, and fonorous porphyry, chemifts have fought for this^^^^^er. 

 alkali in other minerals, and their enquiries have not been 

 difappointed : Tromfdorfl^ has found it lately in the augite, 

 and no doubt this alkali will be met with in many other mi- 

 nerals in which it was not expedted. Being called upon by 

 the company of potters of Stafl'ordfliire to examine a variety 



of 



