17G 



6. Determination of Sodium Sulphate and Carbonate : 



To an aliquot part of the soil solution a measured volume of N/50 sodium 

 carbonate is added in excess of that required for complete decomposition of all 

 calcium and magnesius 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 sodium carbonate in the 

 filtrate is then determined by titration with N/50 sulphuric acid. The quantity 

 of N/50 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 com- 

 bined with Calcium and Magnesium and the total amount already found, gives the 

 proportion combined as Sodium sulphate. Should more N/50 sulphuric acid be 

 required than the quantity of Sodium carbonate originally added, the excess ^over 

 such amount is calculated as Sodium carbonate. By "total alkaline salts" is 

 understood the sum of the Sodium chloride, carbonate, and sulphate. 



7. Determination of Total Lime: 



To an aliquot part of the soil solution two or three drops of rosolic acid are 

 added; then dilute ammonia by means of a dropping tube, and a sufficiency of 

 ammonium chloride to redissolve any precipitated magnesia, after which the liquid 

 is warmed, 20 c.c. of four per cent, ammonium oxalate solution are added, and 

 the determination is further conducted exactly as in the extraction of the soil by 

 hydrochloric acid. It may, however, be found preferable, especially when the 

 quantity of lime is small, to dissolve the oxalate precipitate in dilute sulphuric 

 acid and determine its amount by titration with N/100 Potassium permanganate. 



8. Calcium and Magnesium carbonates and sulphates : 



Any carbon dioxide which may be present in excess of that combined with 

 soda, as Sodium carbonate, is calculated in the first instance as Calcium carbonate. 

 Should this not yet account for all the carbon dioxide, the rest of the latter ir 

 calculated as Magnesium carbonate : on the other hand, if there still remains an 

 excess of Lime unaccounted for, it is calculated as Calcium sulphate. Any excess 

 of Sulphuric oxide which may still remain is assigned to Magnesia.* 



DIVISION OF HEKBERT. 



According to the methods outlined above, determinations of aLkaJine 

 salts were made in the three samples of surface soil from Douglas, referred 

 to in connection with the Division of Herbert (see p. 62). These 

 determinations resulted as follows : | 



Sodium Sodium Sodium Total alka- Calcium Calcium Magne- Magne- Total soluble salt -. 



v chloride, sulphate, carbon- line salts, 'sulphate, carbon- sium sium calculated, found, 

 ate. ate. sulphate, carbon- 

 ate. 



1 -006 .006 -021 -028 '065 '048 



2 -005 '002 '007 '001 '038 '046 '060 



3 '006 '003 -001) '035 '003 '048 '056 



* Should there be more Lime or Magnesia, or both, than required for the sulphuric 

 oxide present, these are in such case calculated as chlorides, a corresponding deduc- 

 tion from the Sodium chloride being made. Under these circumstances the amount 

 of chlorine combined with Magnesium may be checked by determining the chlorine 

 in the heated " total salts " residue, and deducting the figure so obtained from 

 that arrived at under (4), the difference between the two determinations being due 

 to chlorine combined with Magnesium. 



t The results are given in percentages, and, except where the contrary is indi- 

 cated, blanks in the tables denote absence of the particular substances specified. 



