236 AGRICULTURAL ANALYSIS 



process must be freed from this impurity by. removing the precipi- 

 tate from the filter, boiling with water and a little nitrate of am- 

 monia and repeating this treatment, if after the first application 

 of it, the filtrate still shows the presence of magnesia. 



208. Jones' Variation. The method of E. Glaser described 

 above, has been found by Jones to be inaccurate on account of 

 the alcohol not being added in sufficient quantity in the pre- 

 cipitation of calcium sulfate and for the additional reason that the 

 amount of sulfuric acid added is more than is actually necessary. 83 

 A further objection to the method is found in the small quantity 

 of the original material, viz., 0.4 gram, which gives only a small 

 precipitate of iron and alumina, especially in those cases where 

 the samples contain only small quantities of these substances. 

 Jones modifies the method as follows : Ten grams of the material 

 are dissolved in nitro-hydrochloric acid and the solution made up 

 to 500 cubic centimeters and filtered. Fifty cubic centimeters of 

 this solution, representing one gram, are evaporated to 25 cubic 

 centimeters and, while still hot, 10 cubic centimeters of dilute 

 sulfuric acid (one to five) added. The mixture is well stirred 

 and 150 cubic centimeters of 95 per cent, alcohol added and, 

 after stirring, the solution is allowed to stand three hours. The 

 calcium sulfate is collected on a filter, washed with alcohol, and 

 the filtrate and washings collected in an erlenmeyer. The wash- 

 ing is completed when the last 10 drops, after dilution with an 

 equal volume of water, are not reddened with a drop of methyl 

 orange. The filtration is conveniently hastened by a moderate 

 vacuum. 



The moist calcium sulfate is transferred to a platinum cruci- 

 ble, the filter placed on it, the alcohol burned off, the filter inciner- 

 ated, and the calcium sulfate ignited and weighed. The precipi- 

 tate is not sufficiently hygroscopic to offer any difficulties to con- 

 ducting the operations in an open dish. The contents of the flask 

 are heated to expel the alcohol, which is contaminated with hydro- 

 chloric or nitric acid and can not be used again until distilled over 

 an alkali. The residue is washed into a beaker, made slightly 

 alkaline with ammonia, and again heated till all the ammonia is 



n Zeitschrift fur angewandte Chemie, 1891, 4 : 3. 



