152 S. G. WALTON. 



cipitated together as hydroxides and weighed as oxides, 1 

 after which the mixed oxides were dissolved in hydrochloric 

 acid, and after diluting and warming with a little potassium 

 iodide, the liberated iodine was determined by titration 

 with standard sodium thiosulphate. The iodine was calcu- 

 lated into its equivalent of |erric oxide, and the amount 

 thus found deducted from the weight of the total oxides, 

 the difference gives the alumina. This method although 

 little used gives very accurate results. The calcium after 

 removal of the zinc and manganese as sulphides was pre- 

 cipitated as oxalate and weighed first as carbonate and 

 afterwards as oxide, while the magnesium was precipitated 

 as magnesium ammonium phosphate and weighed as pyro- 

 phosphate. I might mention that the precipitates of silica, 

 calcium, and magnesium were tested spectroscopically for 

 traces of barium or strontium without any being detected. 



Sodium and potassium— Four litres of water were taken 

 for this estimation and the usual method for the separation 

 of the calcium and magnesium followed, the metals being 

 weighed as sulphates. It was found, however, that the 

 sulphates contained a small quantity of magnesium. This 

 amount was determined by precipitation as phosphate, 

 calculated to MgS0 4 , and the weight so obtained deducted 

 from the weight of the total sulphates, leaving the weight 

 of the pure sodium and potassium sulphates. I have always 

 found that the whole of the magnesium is not removed by 

 the usual treatment for the estimation of the alkalies, and 

 in order to obtain accurate results, it is absolutely neces- 

 sary to determine the quantity remaining with the sulphates 

 of the alkalies. A number of determinations of the alkalies 

 were made and thus a large quantity of the mixed sulphates 

 of the alkalies was available for the estimation of the 



1 A small amount of phosphate was found together with the oxides, 

 this was estimated and allowed for. 



