Investigations Begarding Brack'' {Alkali) in Cajjc Colony Soils. 133 
3. Determination of Total Carbon Dioxide as Caj^bouates. — An aliquot 
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portion of the above soil solution is very cautiously titrated with sul- 
phuric acid, a few drops of methyl orange, or preferably of phenacetolin, 
being used as indicator ; from the quantity of acid used the total quantity 
of carbon dioxide present as carbonates is calculated. 
4. Determination of Sodium Chloride. — To the aliquot portion used in 
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the last determination a few more drops of sulphuric acid are added, 
then four drops of a chlorine-free potassium chromate solution, and titra- 
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tion is carried on by means of silver nitrate, all the chlorine thus 
determined being calculated as sodium chloride. 
5. Determination of Sidphuric Oxide. — Another aliquot portion of the 
original soil solution is slightly acidulated by means of hydrochloric acid. 
If this causes the flocculation of clay, the mixture is filtered and the 
residue on the filter thoroughly washed. The clear acidulated solution is 
heated to boiling, and a large excess of boiling barium chloride solution is 
then slowly added, the mixture being allowed to continue boiling for five 
minutes. After the precipitate has completely settled the supernatant 
liquid is poured on to a filter ; to the precipitate remaining in the beaker 
is added about 20 c.c. of boiling water, with which it is after thus washing 
transferred to the filter. On the filter the precipitate is again washed, at 
first with distilled water slightly acidulated by hydrochloric acid, and 
ultimately with pure water. The filter is then dried, ignited, and weighed. 
6. Determination of Sodium Sulijliate and Carbonate. — To an aliquot 
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part of the soil solution a measured volume of ^ sodium carbonate is 
added in excess of that required for complete decomposition of all calcium 
and magnesium sulphates, chlorides, and nitrates that may be present. 
The mixture is evaporated to dryness on a water bath, the residue being 
taken up with water and filtered, and the filter thoroughly washed. The 
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sodium carbonate in the filtrate is then determined by titration with ^ 
50 
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sulphuric acid. The quantity of ^ sulphuric acid used in the titration, 
deducted from the total quantity of sodium carbonate originally added, 
gives the equivalents of calcium and magnesium sulphates present. The 
difference between the amount of sulphuric acid thus combined with 
calcium and magnesium and the total amount already found gives the 
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proportion combined as sodium sulphate. Should more sulphuric acid 
be required than the quantity of sodium carbonate originally added, the 
