ON THE ESTIMATION OF POTASH AND PHOSPHORIC ACID. 23 



of sodium chloroplatinatc. The error increases with the amount of sodium, 

 but is never very large, and a correction may be applied if desired. 



3. If Tatlock's method be employed there is no occasion to separate any 

 sulphates, nitrates, or magnesium ; but if the amount of chloride present is 

 insufficient for the existence of all the potassium as chloiido of potassium, 

 the deficiency must be supplied by addition of chloride of sodium or hydro- 

 chloric acid." The results obtained are in many cases very accurate, but 

 have a tendency to be somewhat below the truth. 



-1. There is practically no advantage in drying the cbloroplatinatc of po- 

 tassium at 130° C. rather than at 100° C. The loss at the higher tempera- 

 ture was found not to exceed -07 per cent, of the weight of the precipitate, 

 but is probably governed by the conditions of precipitation. 



5. The Committee is of opinion that a preliminary washing of the preci- 

 pitate of chloroplatinatc of potassium with a solution of platinic chloride is 

 a valuable modification of the usual process. As the method so modified is 

 capable of direct application to the commercial salts of potassium, and does 

 not necessitate the previous removal of sulphates, nitrates, or magnesium, 

 the Committee considers that it deserves to be generally applied for the 

 determination of potassium in commercial products containing that metal. 



So far the Committee has not thought it necessary to make any experi- 

 ments on other methods of determining potassium than that in which it is 

 converted into chloroplatinatc 



Statement of the Results of Analysis of Potash Salts. 



Your Committee has devoted considerable attention to the difficult question 

 of the proper mode of stating the results of analyses of potash salts. 



Hitherto the statements of various analysts appear to have been charac- 

 terized by a lamentable want of system, and in many cases they are greatly 

 at variance with the generally accepted principles of chemical combination 

 and double decomposition. 



The Committee has been furnished with copies of analyses of potash salts 

 in which carbonate of potassium is reported as coexistent with sulphate and 

 chloride of sodium, and the cases are numerous in which similar anomalous 

 statements occur. 



These various modes of statement are by no means solely due to eccentric 

 notions respecting chemical affinity, but appear in many cases to be owing 

 to the desire to attribute as high or low (as the case may be) a commercial 

 value to the article analyzed as is compatible with its percentage composi- 

 tion. Thus a commercial carbonate is chiefly valuable on account of the 

 potassium carbonate it contains ; aud therefore if the whole of the potassium 

 be stated as existent in that form, while the valueless sulphate and chloride 

 arc relegated to the sodium, the apparent value is considerably greater than if 

 only that portion of the potassium be assumed to exist as carbonate which 

 is in excess of the quantity necessary to combine with the more powerful 

 salt radicals. 



The Committee believes it would be practically impossible to lay down 

 general rules for statement of results which, if followed, would necessarily 

 and invariably lead to an exact and scientific statement of the mode of 

 existence of the various metals and salt radicals in a complex commercial 

 salt of potash ; but it is of opinion that whatever modifications in detail 

 individual analysts may think proper to adopt, the following general prin- 

 ciples should be adhered to : — 



