114 fairchild: phosphoric acid determination 



Of course carbon and various electrolytes may be used instead 

 of the metals, with even smaller corrections but the temperature 

 resistance coefficients of these are so large that they are generally 

 less suitable for use as resistances than constantan or manganin. 



When a greater current carrying capacity is desired the wires 

 may be frequently used in parallel soldered between parallel 

 metal strips, provided the spacing is not too small. 



ANALYTICAL CHEMISTRY.— The accurate volumetric deter- 

 mination of phosphoric acid in phosphate rock. John G. 

 Fairchild. Communicated by F. W. Clarke. To appear 

 in the Journal of Industrial and Engineering Chemistry. 



The method here proposed is a modification of Pemberton's 

 caustic alkali titration. In its original form Pemberton's method 

 gives results 1.5 per cent low in comparison with the standard 

 method of weighing the phosphoric acid as magnesium pyrophos- 

 phate. This error is reduced to zero by precipitation of the sol- 

 uble phosphate with barium chloride in excess. The greatest 

 error resulting in the analysis of eight phosphate rocks by this 

 method was 0.32 per cent of P 2 6 , parallel determinations being 

 made by the gravimetric method. The average error was 0.03 

 per cent of P 2 5 . The accuracy is 99 per cent as compared with 

 an accuracy of 99.5 per cent for the gravimetric method. The 

 advantage of the volumetric method is its rapidity, not more 

 than one hour being required for a complete determination. 

 Attention is called to the fact that the barium phosphate precip- 

 itated undergoes hydrolysis, necessitating moderate sized portions 

 for titration. Also, that without this modification the apparent 

 percentage of phosphoric acid is less, the larger the portions 

 titrated. 



GEOLOGY. — Age of the Worcester phyllite. David White. 



The Worcester phyllite consists largely of altered clay shales, 

 some of which are very highly carbonaceous, but comprises also 

 thin beds of sandy shale and sandstone. The rock, which has 

 generally been termed an argillite, is, under the name phyllite, 



