METHODS OF CLAY ANALYSES. 49 



pared with that obtained from a standard of titaniunj 

 sulphate. 



Sulphur (total present ) -^The sulphur is deter- 

 mined by fusing one-half gram of clay with a mixture 

 of sodium carbonate, five parts, and potassium nit- 

 rate, one part. The melt is brought into solution with 

 hydrochloric acid. The silica is separated by evapora- 

 tion, heating, resolution, and subsequent filtration. 

 Hydrochloric acid is added to the filtrate to at least 

 five per cent, and the sulphuric acid is precipitated 

 by adding barium chloride in sufficient excess, all solu- 

 tions being boiling hot. The barium sulphate is fl.lt- 

 ered off and washed with hot water, burned and weigh- 

 ed as such. 



Ferrous Oxide- — is determined by fusing one-half 

 gram of clay with five grams sodium carbonate, the 

 clay being well covered with the carbonate, the top be- 

 ing upon the crucible. The melt is dissolved in a'mix- 

 ture of dilute hydrochloric and sulphuric acids in an 

 atmosphere of carbon dioxide. The ferrous iron is 

 determined at once by titration with a standard pot- 

 assium permanganate solution. 



The rational analysis is made from the results ob- 

 tained by the chemical analysis in the following way : 

 The alumina found in the portion insoluble in sul- 

 phuric acid and sodium hydroxide is multiplied by 

 3.51. This factor has been found to represent the 

 average ratio between alumina and silica in orthoclase 

 feldspar; therefore the product just obtained would 

 represent the amount of silica that would be present 

 in undecpmposed feldspar. The sum of this silica with 

 the alumina, ferric oxide and alkalies equals the 

 "feldspathic detritus." The difference between silica 

 as calculated for feldspar and the total silica in the 

 insoluble portion represents the "quartz" or "free 



