42 METHODS OF ANALYSIS [Chap. 



38 FREE CARBON DIOXID.— TENTATIVE. ' 



If the water reacts acid to phenolphthalein and alkaline to methyl orange, titrate 

 100 cc. with N/20 sodium carbonate (free from bicarbonate) until the solution ia 

 neutral to phenolphthalein. The number of cc. used multiplied by 1.1 gives the 

 milligrams of free carbon dioxid in 100 cc. Express results in milligrams per liter. 



39 CARBONIC AND BICARBONIC ACIDS.— OFFICIAL. 



To 100 cc. of the water add a few drops of phenolphthalein and, if a pink color is 

 produced, titrate with N/20 crystallized potassium hydrogen sulphate or sulphuric 

 acid, adding a drop every 2 or 3 seconds, until the red color disappears. Multiply 

 the burette reading by the factor 3 which gives the milligrams of the carbonic acid 

 ion in 100 cc. To the colorless solution from this titration, or to the original solution 

 if no color is produced with phenolphthalein, add 1 or 2 drops of methyl orange; con- 

 tinue the titration without refilling the burette and note the total reading. If 

 carbonic acid is absent, multiply the total burette reading by the factor 3.05, which 

 gives the value of the bicarbonic acid ion in milligrams per 100 cc. If carbonic acid is 

 present, multiply the reading with phenolphthalein by 2 and subtract from the total 

 reading of the burette. Multiply the difference by 3.05, which gives the bicarbonic 

 acid ion in milligrams per 100 cc. Express results in milligrams per liter. 



Silica, Iron, Aluminium, Calcium. Strontium and Magnesium. 



40 silica.-official. 



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

 approximate quantity of calcium and magnesium present, in order to ascertain 

 the quantity of water to be evaporated for the final analysis. 



Evaporate a quantity, usually 1-5 liters, of the water sufficient to yield 0.1-0.6 

 gram of calcium oxid or 0.1-1 gram of magnesium pyrophosphate. Acidify the 

 water with hydrochloric acid and evaporate on the water bath to dryness in a plati- 

 num dish; continue the drying for about an hour. Thoroughly moisten the residue 

 with 5-15 cc. of hydrochloric acid (1 to 1). Allow to stand 10-15 minutes and add 

 sufficient water to bring the soluble salts into solution. Heat on the steam bath 

 until solution of the salts is effected. Filter to remove most of the silica and wash 

 thoroughly with hot water. Evaporate the filtrate to dryness; treat with 5-10 cc. 

 of the hydrochloric acid and sufficient water as above. Heat, filter, and wash 

 thoroughly with hot water. Designate the filtrate as A . Transfer the 2 residues to 

 a platinum crucible, ignite, heat over a blast lamp and weigh. Moisten the contents 

 of the crucible with a few drops of water. Add a few drops of concentrated sulphuric 

 acid and a few cc. of hydrofluoric acid and evaporate on the water bath under a good 

 hood. Repeat the treatment if all the silica is not volatilized. Dry carefully on a 

 hot plate, ignite, heat over a blast lamp, and weigh. The difference between the 

 two weights 'S the weight of the silica. The residue in the crucible consists of alumin- 

 ium and iron oxids. The weight of this residue is added to that of the total alumin- 

 ium and iron oxids obtained in 41 . (If the above residue weighs more than 0.5 mg., 

 barium sulphate may be found here when barium is present in the water. If so, 

 make the necessary correction and add to the weight of the total iron and aluminium 

 oxids in 41 .) 



41 IRON AND aluminium.— OFFICIAL. 



Concentrate A , under 40, to about 200 cc. ; while still hot, add ammonium hydroxid 

 slowly with constant stirring until alkaline to methyl orange. Boil, filter, and wash 

 2 or 3 times with hot water. Dissolve the precipitate in hot hydrochloric acid. 



