102 Dr. Perc/s Chemical Examination of Lettsomite, 



The peroxide of iron was redissolved in hydrochloric acid 

 and precipitated by ammonia ; washed and ignited, it weighed 

 0*05. 



In every instance the washing of the precipitates was con- 

 tinued until the wash-water either ceased to be rendered in 

 the slightest degree turbid by nitrate of silver, or to leave an 

 appreciable residue by evaporation. 



Phosphoric acid was sought for in the alumina obtained in 

 the second analysis, and detected both by Berzelius's process 

 (fusing with silica and carbonate of soda, and subsequent pre- 

 cipitation by ammonia and chloride of magnesium), and Svan- 

 berg's test, molybdate of ammonia. But by the latter test 

 phosphoric acid was also detected in the potash used in the 

 preceding analysis, although prepared with alcohol. And 

 the same test also indicated its presence in the carbonate of 

 potash from which the potash was derived. On testing the 

 mineral directly with molybdate of ammonia, I did not detect 

 phosphoric acid ; and I have obtained the same result with 

 another specimen of velvet ore, which I have recently received 

 from Berlin. I am particular in stating these facts, because 

 it is obviously of great importance to the analytical chemist 

 that his potash should be free from phosphoric acid, especially 

 in the separation of alumina from iron*. 



Matrix. — It consists chiefly of hydrated peroxide of iron, 

 but contains also alumina, lime, oxide of copper, sulphuric 

 acid, silica, and a trace of phosphoric acid (by Svanberg's 

 test). Here and there upon the surface is some amorphous 

 white matter, which is probably a basic sulphate of alumina, 

 as it contains alumina and sulphuric acid. 



Results tabulated. 



First analysis. Second analysis, 



grs. grs. 



1. Weight of mineral . 2*99 4<'25 



2. CuO 1'44< 1*98 



3. BaS03 l-34. = 0'46SO3 l-74 = 0-60SO3 



4. AP03 and\ ^ .^ 0-47 



5. Fe^Oa J * * * "'^^ 0-05 



6. HO 0*98 



7. Matter after heating\ „ , „ 



insoluble dilute NO^ J •" "*^" 



* I have found, I believe, an exact method of separating alumina from 

 iron without the use of potash, which I hope shortly to publish with the re- 

 quisite analytical proofs. 



