26 



REPORT 1877. 



indirect determinations ; but the Committee strongly recommends the em- 

 ployment of direct processes whenever possible. 



In all cases where such a course is possible it is very desirable that the 

 various compounds of potassium present should be calculated into the salt 

 which the name of the article indicates as the leading constituent of tho 

 sample. In the case of sulphates, muriates, and carbonates, the correspond- 

 ing amount of anhydrous potash should bo stated. Thus the Committee 

 recommends that an analysis of a German muriate should be stated some- 

 what in the following manner : — 



Centesimal composition. 



Calcium Sulphate. 

 Potassium Sulphate. 

 Potassium Chloride. 

 Sodium Chloride 

 Magnesium Chloride. 

 Insoluble Matter. 

 Water. 



A. 

 B. 



100-00 



=Potassium Chloride. 



B 



B + a. 



= Anhydrous Potash. 



X 



y 



x+y 



In the case of carbonates, the anhydrous potash corresponding to the car- 

 bonate of potassium present should always be stated separately from that 

 calculated from the sulphate and chloride, as it is only in certain cases that 

 the potassium existing in the latter forms is of any real value 



Third Report of a Committee, consisting of E. C. C. Stanford A 

 E. Fletcher, J. Dewar, E. W. Parnell, T. W. Ogilvie, and 

 Alfred H. Allen {Secretary), on the methods of estimating Potash 

 and Phosphoric Acid in Commercial Products containing them, and 

 on the Statement of the results. Braion up by Alfred H. Allen. 



Estimation of Potash. 



Although the process of determining potassium by precipitation with 

 chloride of platinum is Ihe method almost universally adopted by chemists of 

 large experience m tho assay of commercial potash salts, the Committee 

 thought it desirable to investigate also the volumetric method of Stolba, 

 which is based on the precipitation of potassium as silicofluoridc and the 

 titration Ox the precipitate with standard alkali, according to the equation— 

 K 2 SiP G + 4KHO = 6KF + H.SiO,. 



This process is thus described on page 176 of the 7th English edition of 

 iresemuss 'Quantitative Analysis':— "To. the moderately concentrated 

 solution of the potash salt in a beaker add a sufficiency of hydro- 

 ihiosilicic acid, and then an equal volume of pure strong spirit The 

 silicofiuoiide of potassium will separate as a translucent precipitate. When 

 it has settled, filter, wash out the beaker with a mixture of equal parts strong 

 spmt and water, and wash the precipitate with the same mixture till the 

 washings are no longer acid to litmus paper. Put the filter and precipitate 



