384 Mr. Smithson on the Discovery of [May, 



lime, and imbedded in a greyish-coloured substance which I 

 suppose to be also new to mineralogy. 



The colour of latrobite approaches to pink like some of the 

 deep coloured varieties of lepidolite. 



Its specific gravity is about 2*8. 



It scratches glass, and is scratched by felspar. 



It has cleavages in three directions, parallel to the lateral and 

 terminal planes of a doubly oblique prism, P on M, 98° 30'; 

 P on T, 91° ; M on T, 93° 30'. (See the figure already given.) 

 The plane parallel to P is very dull, and the measurement 

 obtained from it not to be confidently relied on ; those parallel 

 to M and T afford good reflections, but one of these is brighter 

 than the other. 



I send herewith specimens of the arfwedsonite and latrobite, 

 which you will, perhaps, take the trouble to analyze at your 

 leisure; and I remain, yours truly, 



H. J. Brooke. 



Article XIII. 



On the Discovert/ of Acids in Mineral Substances. 

 By James Smithson, Esq. FRS. 



(To the Editor of the Annals of Philosophy.) 



SIR, April 12, 1823. 



Acids, it is well known, have been repeatedly overlooked in 

 mineral substances, and hence dubiousness still hovers over the 

 constitution of many, although they have formed the subjects of 

 analysis to some of the greatest modern chemists. 



To be able to dissipate all doubts — to ascertain with certainty 

 whether an acid does or does not exist, and, if one is present, 

 its species, and this with such facility that the trial may be inde- 

 finitely renewed at pleasure, and made by all, so that none need 

 believe but on the testimony of his own experiments, is the 

 degree of analytical power which it would be desirable to 

 possess. 

 . So far as I have gone in these respects, I here impart. 



As the carbonates of soda and of potash precipitate all the 

 solutions of earths and metals in acids, so do they decompose 

 all their salts by fusion with them. Fusion with carbonate of 

 soda or potash affords there a general method of separating 

 acids from all other matters. 



Lead forms an insoluble compound with all the mineral acids 

 except the nitric. It may consequently be immediately known 

 whether a mineral does or does not contain an acid element by 



