283 COTTER: SODA INDUSTRY OF SIND. 



This method prevents any loss of C0 2 . It was checked by 

 titrating pure sodium carbonate, when it was found that exactly 

 half the quantity was required to the end-point of the phenol- 

 phthalein. There are still difficulties in using this method of testing, 

 as the personal equation enters largely into the determination of 

 the end-points, which are difficult to fix. It is necessary to practise 

 first upon pure sodium carbonate before titration, to use very 

 minute quantities of indicator, to take the same amounts of solu- 

 tion and as nearly as possible the same strengths of alkali, and to 

 use the same number of drops, (not more than two, preferably one) 

 of indicator in each experiment. Titration must be carried on 

 exactly to the end-points indicated in F. K. Cameron's paper, 

 viz., to complete loss of colour of the phenol-phthalein, and to the 

 first change of the methyl-orange. 



