ERUPTIVE BOOKS. 



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TABLE IH. Determinations of lead, nine, cobalt, and barium, chiefly in eruptive rocks. 



(Complete analysis in Table I. 



X. B. The blauk spaces under the headings PbO, etc., do not indicate absence of the respective oxides. Where no 

 results are given, no tests were made. 



REMARKS ON TABLES I, II, AND III. 



Insoluble silicates were decomposed by fusing with alkaline carbonates for the 

 determination of silica, titauie acid, aud all bases except tbe alkalies. 



Ferric oxide and alumina were separated either by pure potassium hydrate, or 

 more generally by ammonium sulphide, after addition of tartaric acid and ammonia. 



For the determination of ferrous oxide, treatment with sulphuric acid in sealed 

 tubes at about 1300 C. was employed in cases where complete decomposition of the 

 silicates could thus be effected, and the solution titrated with potassium permanganate. 

 For the decomposition of refractory silicates, pure hydrofluoric acid, distilled from 

 a platinum retort, was employed, the solution being effected in platinum vessels with 

 careful exclusion of air. The iron was then determined as above. 



