IV] WATERS 51 



TOTAL HARDNESS."— TENTATIVE. 



75 REAGENTS. 



(a) Soda reagent. — Prepare a N/10 alkali solution, using equal parts of sodium 

 hydroxid and sodium carbonate. Standardize the solution by titration against 

 N/20 sulphuric acid, using erythrosin as indicator. 



76 DETERMINATION, 



Add sufficient N/20 sulphuric acid to 200 cc. of the sample to neutralize the alkalin- 

 ity, the amount required for this purpose being calculated from the results obtained 

 as directed under 72. Concentrate to 100 cc, add 25 cc. of the soda reagent, and 

 again boil down to 100 cc, using a porcelain, silver, or platinum dish. Cool, rinse 

 into a 200 cc. volumetric flask and dilute to 200 cc. with freshly boiled and cooled 

 water. Filter through a dry paper, reject the first 50 cc. of the filtrate, and titrate 

 100 cc. of the filtrate, using N/20 sulphuric acid and chloroform with erythrosin as 

 indicator, as directed under 72. Calculate the total hardness by the following 

 formula: H = 12.5 (S-2N) in which 



H = total hardness expressed as parts per million of calcium carbonate. 



S = number of cc. of N/20 sulphuric acid equivalent to the 25 cc. of the soda 

 reagent used. 



N = number of cc. of N/20 sulphuric acid used in titrating back the excess of 

 the soda reagent. 



77 PERMANENT OR NON-CARBONATE HARDNESS.— TENTATIVE. 



The difference between the alkalinity before boiling 72 and the total hardness 76 

 is the permanent or non-carbonate hardness expressed as parts per million of cal- 

 cium carbonate. 



IRRIGATING WATER. 



78 GENERAL METHODS.— OFFICIAL. 



Determine the solids in solution, chlorin, carbonic and bicarbonic acids, sulphuric 

 acid, calcium and magnesium as directed under 7, 19, 39, 48, 45, and 47 respec- 

 tively. To make the hypothetical combination, calculate calcium and magnesium 

 to the acid ions in the following order: bicarbonic, sulphuric and chlorin. Then 

 calculate the remaining acid ions, including carbonic, to the corresponding salts of 

 sodium. 



BLACK ALKALI.— OFFICIAL. 



79 REAGENTS. 



(a) N'/50 sodium carbonate. — One cc. of this solution is equivalent to 0.00106 

 gram of sodium carbonate. 



(b) N/50 sulpJmric acid. — One cc. of this solution is equivalent to 0.0010 gram of 

 calcium carbonate or 0.00136 gram of calcium sulphate. 



(C) Enjihrosin indicator. — Dissolve 0.25 gram of the sodium salt in 1 liter of water, 

 (d) Chloroform. — Neutral to erythrosin. 



80 DETERMINATION. 



Transfer 200 cc. of the water to a platinum or silver dish, add 50-100 cc. of N/50 

 sodium carbonate, according to the amount of soluble salts of calcium and magnesium 

 present, and evaporate to dryness. Rub up the residue with carbon dio-xid-free 

 water. 



