50 METHODS OF ANALYSIS [Chap. 



Q6 IRON AND ALUMINIUM.— OFFICIAL. 



Determine as directed under 41 . 



67 CALCIUM.— OFFICIAL. 



If no phosphoric acid is present, concentrate the filtrate from the determination 

 of iron and precipitate with ammonium hydroxid and oxalate as directed under 45. 

 Usually one precipitation is sufficient. 



$8 MAGNESIUM.— OFFICIAL. 



Determine as directed under 47. 



69 SULPHURIC ACID AND ALKALIES. -OFFICIAL. 



Follow the methods described under 48 and 49. Generally, however, for tech- 

 nical purposes it is sufficiently accurate to determine the acids and the bases, 

 except sodium and potassium, and then to calculate the excess of acid over basic 

 ions to the sodium salt, and state the alkali thus found as sodium and potassium by 

 difference. 



70 TEMPORARY HARD NESS. 7— TENTATIVE. 



The difference between the alkalinity after boiling, 74, and the alkalinity before 

 boiling, 72, is the temporary hardness in parts per million of calcium carbonate. 



ALKALINTTY-Before BoiUng. 



71 REAGENTS. 



(a) N /50 sulphuric acid. 



(b) Erythrosin indicator. — Dissolve 0.1 gram of the sodium salt in 1 liter of water. 

 (C) Chloroform. — Neutral to erythrosin. 



72 



DETERMINATION. 



Measure 100 cc. of the water into a 250 cc. white, glass-stoppered bottle, add 2.5 cc. 

 of the erythrosin and 5 cc. of the chloroform, add X/50 sulphuric acid in small quanti- 

 ties, shaking the bottle vigorously after each addition of the acid. The rose color 

 gradually disappears and is finally discharged by 1 or 2 drops of the acid. A white 

 paper held back of the bottle facilitates the detection of the end point. Multiply 

 the number of cc. of N/50 sulphuric acid used by 10 to obtain the number of parts per 

 million of alkalinity in terms of calcium carbonate. 



Boil 100 cc. of the water in a porcelain dish gently for 30 minutes. Cool, transfer 

 to a 100 cc. volumetric flask and fill to the mark with recently boiled and cooled 

 water. Filter through a dry paper and determine the alkalinity of the filtrate as 

 directed under 72, making the proper calculation for the aliquot employed and cal- 

 culating in terras of calcium carbonate the parts per million of alkalinity after 

 boiling. 



