MODIFIED METHOD 613 



ner. The phosphoric acid is then determined in another aliquot 

 part of the original filtrate from the first solution of the ash. 



Since most ashes contain an excess of phosphoric acid above 

 the quantity required to combine with the iron it is preferable to 

 proceed as described in the next paragraph. 



520. Modified Method. The principle of the method rests on 

 the assumption that all the phosphoric acid may be removed 

 from the solution by the careful addition of iron chlorid. Any 

 excess of iron is then removed by ammonium acetate and the 

 manganese, lime, and magnesia are separated in the filtrate. The 

 percentage of iron is determined by reduction of the iron in an- 

 other portion of the solution and titration with potassium per- 

 manganate. The process as conducted by McElroy is as fol- 

 lows : 80 



Moisture. If the ash contain much carbon the water is best 

 determined by drying in vacuo to avoid oxidation. 



Sand, Silica, and Carbon. Place a portion of the ash in a 

 weighed platinum dish, weigh, and cover the sample with hydro- 

 chloric acid of 1.115 specific gravity. Evaporate to dryness on 

 the water bath, and then heat for 15 minutes at 105 to no 8 in 

 an air bath. Repeat the treatment with acid and drying : Finally 

 cover with a third portion of acid and digest on the water bath 

 for an hour or two. Filter into a weighed gooch and wash the 

 residue free of chlorids. The gooch is best weighed with the dish 

 to avoid the necessity of transferring the silica which may adhere 

 to the sides of the former. Dry at a few degrees above the boil- 

 ing temperature of water and weigh. Where the ash contains 

 much charcoal the drying is best done in a vacuum at from 60 

 to 70. The increase in weight found represents sand, silica, and 

 carbon : Burn and reweigh. The loss is carbon. 



Another portion of ash is treated as before except that it is 

 filtered through a paper filter. The filtrate is united with that of 

 the previous sample in a graduated flask. When the washing is 

 completed the filter is placed in the dish, a weak solution of 

 caustic soda added, and the mixture heated on the water bath 

 for some time. Decant while hot through a fresh filter and re- 

 86 Manuscript, Unpublished. 



