52 METHODS OF ANALYSIS 



For this purpose distilled water should be vigorously boiled until approximately 

 one third of the original volume is evaporated, then cooled and stoppered. An 

 ordinary laboratory wash bottle should not be used to transfer the residue, as the 

 carbon dioxid from the breath of the operator is sufficient to vitiate the results. 



Transfer to a 100 cc. graduated flask, make up to the mark, shake thoroughly, and 

 allow to stand until clear (12-15 hours). Remove 50 cc. of the clear, supernatant 

 liquid, equivalent to one half of the original quantity of water and sodium carbonate 

 added, and transfer to a stoppered titrating bottle, of 250 cc. capacity, of clear glass 

 without any tinge of pink. Add 5 cc. of the chloroform and 1 cc. of the erythrosin 

 and titrate with the standard acid until the color disappears. Shake the solution 

 vigorously after each addition of the acid; the chloroform produces a milkj^ appear- 

 ance which makes the reading of the end point sharp and certain. 



(1) If less sulphuric acid is required than is equivalent to one half of the sodium 

 carbonate added, due to some of the sodium carbonate reacting with soluble salts of 

 calcium and magnesium, the solution originally contained no black alkali in excess 

 but rather an excess of the so-called permanent or non-carbonate hardness. It is 

 customary to express the hardness in terms of calcium carbonate or calcium sul- 

 phate. With irrigating waters the latter form is to be preferred. Therefore, the 

 difference between the number of cc. of the sulphuric acid required and one half of 

 the number of cc. of the sodium carbonate added multiplied by the factor 0.00136 

 gives the equiA^alent of calcium sulphate in 100 cc. of the water. 



(2) If more sulphuric acid is required than that equivalent to one half of the 

 sodium carbonate added, black alkali was originally present in the solution and the 

 difference in cc. multiplied by the factor 0.00106 gives the black alkali in terms of 

 sodium carbonate in 100 cc. of water. 



BIBLIOGRAPHY. 



1 Fresenius. Quantitative Chemical Analysis. Revised and amplified trans- 

 lation of the 6th German ed., 1906, 2: 204. 



2 Ber., 1888, 21: 2843; Rept. Mass. State Board of Health, 1890, 2: 722. 



» J. Am. Chem. Soc, 1911, 33: 362; Standard Methods of Water Analysis. Am. 

 Pub. H. Assoc, 2nd ed., 1912, pp. 61 and 62. 



« Sutton. Volumetric Analysis, 10th ed., p. 303; Analyst, 1901, 26: 141, 



5 Am. Chem. J. 1887, 9: 33; U. S. Geol. Surv. Bull. 422, 175. 



«Am. Chem. J. 1887,9: 23. 



^ Standard Methods of Water Analysis. Am. Pub. H. Assoc, 2nd ed.. 1912. dd. 

 36 and 37. > , , ff 



» Ibid, pp. 40 and 41. 



i 



