86 T. Lyttleton Lyon and James A. Bizzell 



Calcium, magnesium, potassium, and sodium. — To determine the 

 calcium, magnesium, potassium, and sodium content, about 10 grams 

 of the air-dried sample was ground in an agate mortar to a practically- 

 impalpable powder. A 4-gram portion of this powder was placed in 

 a platinum dish and saturated with dilute sulfuric acid (1:1). The 

 excess of sulfuric acid was expelled by gentle heat over a free flame, and 

 the mass was allowed to cool. About 5 cubic centimeters of hydrofluoric 

 acid was added to the dish and then evaporated to apparent dryness 

 on the water bath. The treatment with hydrofluoric acid and evaporation 

 on the water bath was repeated three times, 1 cubic centimeter of dilute 

 sulfuric acid being added at the final treatment. The mass was then 

 heated gently until the excess of sulfuric acid was removed, and it was 

 then cooled, moistened with concentrated hydrochloric acid, and allowed 

 to stand for one hour. Water was then added and the whole was gently 

 heated. In case an insoluble residue resulted after this treatment, the 

 mixture was heated for some time on a water bath, and was then allowed 

 to settle and the clear hquid was decanted. The residue was washed 

 two or three times by decantation, and the treatment with hydrofluoric, 

 sulfuric, and hydrochloric acids was repeated until the silica was entirely 

 removed. The hydrochloric acid solution was then evaporated to dry- 

 ness on the water bath, and the residue was saturated with dilute sulfuric 

 acid and heated to a low red heat to remove the excess of sulfuric acid 

 and to convert the sulfates of iron and aluminum to oxides. The resi- 

 due was extracted with dilute hydrochloric acid and thoroly washed. In 

 the filtrate were usually found small quantities of iron and aluminum. 

 These were precipitated by the addition of ammonium hydroxide and 

 filtered, and the precipitate was thoroly washed. The filtrate and washings 

 were concentrated to about 75 cubic centimeters and used for the deter- 

 mination of calcium according to the official method described in Bulletin 

 107 (revised) of the United States Bureau of Chemistry, page 15. The 

 filtrate and washings from the calcium precipitate were made up to 

 200 cubic centimeters, one-half of which was used for the determination 

 of magnesium according to the official method described on page 16 of 

 the bulletin cited above, and one-half for the determination of potassium 

 and of sodium by the ofl&cial method described on page 17 of the same 

 publication. 



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