44 METHODS OF ANALYSIS [Chap. 



the precipitate once or twice by decantation with 1% ammonium oxalate solution. 

 Dissolve the precipitate in hydrochloric acid, dilute to 100-200 cc, add a little 

 oxalic acid, and precipitate as above. After standing 3 hours, filter, wash with the 

 ammonium oxalate solution as above, dry, ignite, heat over a blast lamp, and weigh 

 as calcium and strontium oxids. Subtract from this weight, the weight of strontium 

 oxid equivalent to the strontium under 46. The difference is the weight of calcium 

 oxid. Calculate to calcium. Designate the filtrate and washings as C. 



As a check on the calcium oxid, evaporate to dryness the filtrate from the stron- 

 tium nitrate under 46, beginning with "Filter, wash with ether-alcohol mixture, 

 etc.," dissolve the calcium nitrate in water, precipitate as oxalate, filter, wash, 

 ignite, and weigh as calcium oxid. 



46 STRONTIUM.— TENTATIVE. 



Dissolve the oxids under 45 in dilute nitric acid and test with the spectroscope for 

 strontium. If strontium is present, transfer the nitric acid solution to a small 

 Erlenmeyer flask. Evaporate nearly to dryness over a low flame and heat in an 

 air bath at 150°-160°C. for 1 or 2 hours after the water is evaporated. Break up the 

 dried material with a stirring rod, add 10-15 cc. of a mixture of equal parts of absolute 

 alcohol and ether to dissolve the calcium nitrate. Cork the flask and allow to stand 

 with frequent shaking for 2 hours or longer. Decant the solution through a 5.5 cm. 

 filter, preserving the filtrate. Wash the residue several times by decantation with 

 small portions of ether-alcohol solution. Dry the residue and the filter paper and 

 wash the filter paper repeatedly with small portions of hot water, collecting the 

 filtrate in the flask containing the main portion of the strontium nitrate residue. 

 Add 1 or 2 drops of dilute nitric acid, evaporate, dry, pulverize, and treat with 

 10-15 cc. of ether-alcohol mixture as above. Cork the flask and let stand about 12 

 hours with occasional shaking. Filter, wash with ether-alcohol mixture until a few 

 drops of the filtrate evaporated on a watch glass leave practically no residue. Dry 

 the paper and precipitate. Dissolve the strontium nitrate in a few cc. of hot water. 

 Add a few drops of sulphuric acid, then a volume of alcohol equal to the volume of 

 the solution and allow to stand 12 hours. Filter, ignite, weigh as strontium sulphate 

 and calculate to strontium. Test spectroscopically for absence of calcium. 



47 MAGNESIUM.— OFFICIAL. 



Concentrate C, under 45, to about 200 cc. ; add 2-3 grams of diammonium hydrogen 

 phosphate and sufficient hydrochloric acid to clear the solution when the arnmonium 

 phosphate is all dissolved; disodium hydrogen phosphate or sodium ammonium 

 hydrogen phosphate may be used instead of the diammonium hydrogen phosphate. 

 When cold, make slightly alkaline with ammonium hydroxid, stirring constantly. 

 Add 1-2 cc. excess of ammonium hydroxid and allow to stand about 12 hours. Filter 

 off the supernatant liquid and wash 3 or 4 times by decantation with a solution of 

 2.5% ammonium hydroxid. Dissolve the precipitate in hydrochloric acid, dilute to 

 about 150 cc, add a little diammonium hydrogen phosphate and precipitate with 

 ammonium hydroxid as before. Allow to stand 6-12 hours, filter, wai.?h free from 

 chlorin, ignite, heat over a blast lamp, and weigh as magnesium pyrophosphate. 

 (Cf. II, 16). Calculate to magnesium. 



Sulphuric Acid, Sodium, Potassium and Lithium. 



48 sulphuric acid.— official. 



Make a preliminary examination, using 100-250 cc. of the water to determine the 

 approximate quantity of sulphates. The alkali salts present can be approximated 



