METHODS OF ANALYSIS. 37 
aliquots of the above liquid for determining carbonates, bicarbonates, chlorids, 
sulphates, calcium, magnesium, and sodium. é 
Follow the methods given for determining these constituents in waters in 
Bulletin 91, Bureau of Chemistry, U. S. Department of Agriculture, except 
“in one particular, which is as follows: 
When the salts are obtained in a hydrochloric acid solution, ready for the 
determination of calcium, magnesium, and sodium, pass through hydrogen sul- 
phid to get rid of copper. Filter, evaporate to dryness, again take up in hydro- 
chlorie acid, and determine calcium, magnesium, and sodium in aliquots of this 
soiution. 
Black alkali. 
Solutions required: (1) A standard N/50 sodium carbonate solution. (2) 
A standard N/50 sulphuric acid solution. (8) A solution of erythrosin con- 
taining 0.25 gram to a liter of water. (4) Chloroform. 
MetuHop: Transfer 200 ce of the soil extract, obtained as in the preceding 
method, to a platinum dish, add 50 to 150 ce of standard sodium carbonate 
according to the amount of soluble salts of calcium and magnesium present, 
and evaporate to dryness. Rub the residue up with distilled carbon-dioxid- 
free water, transfer to a 100 ce graduated flask, make up to the mark, shake 
thoroughly, stopper, and allow to stand until clear. When clear, carefully 
remove 50 ce without disturbing the residue in the bottom of the flask and trans- 
fer to the titrating bottle. For this purpose use a bottle of the best color- 
less glass without any tinge of pink, with ground glass stopper and of about 
250 ce capacity. Add 5 ce of chloroform and 1 ce of erythrosin and titrate 
the solution with the standard acid until the color disappears. The solution 
should be vigorously shaken after each addition of acid, the chloroform pro- 
ducing a milky appearance, which makes the reading of the end point sharp 
and certain. : 
If less sulphuric acid is required than that necessary to balance one-half of 
the sodium carbonate added, it iS evident that some of the sodium carbonate 
has been used up and that the solution originally contained no black alkali. 
If, on the other hand, more sulphuric acid is required than that equivalent to 
one-half of the sodium carbonate added, then black alkali was originally present 
and can be calculated from the amount of standard sulphuric acid used in ex- 
cess of that necessary to neutralize one-half the sodium carbonate originally 
added. 
WATERS. 
Total copper. 
Shake sample thoroughly till well mixed with sediment and use 500 ee for 
analysis. Evaporate to dryness in a porcelain dish and determine total copper 
by the same methods used for total copper in soils. 
Soluble copper. 
Filter off 1,000 to 2,000 ce of the water from its sediment. Evaporate to dry- 
ness, take up with 1 or 2 ce of nitric acid by the aid of heat, dilute, filter, and 
determine soluble copper by the method used for soluble copper in soils. 
Soluble salts. 
Filter off 1,000 to 2,000 ce of the water from its sediment and determine ear- 
bonates, bicarbonates, chlorids, sulphates, calcium, magnesium, and sodium, 
according to the methods given for these constituents in waters in Bulletin 91, 
Bureau of Chemistry, U. S. Department of Agriculture. 
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