175 



per cent, of carbonate was harmful, and '4 generally fatal. Maize was 

 least affected of the cereals. Wheat grew well in the presence of '137 

 per cent, of carbonate, but was destroyed by '2 per cent. Legumes are 

 IP ore affected than cereals, but even the latter were fatally affected if the 

 soil around their roots contained a proportion of '2 per cent, of sodium 

 carbonate. 



METHODS OF ANALYSIS. 



The chemical analysis of an alkaline soil is far from being as 

 empiric in its nature, and in the method by which its results have to be 

 interpreted as is the case with the investigations into the proportions of 

 plant food in soils. There is therefore not always the same necessity, 

 when tabulating results of analyses of alkaline soils to specify particularly 

 ihe methods adopted by the analyst. And yet it is for many reasons not 

 only convenient, but also advisable that the methods employed in Gov- 

 ernment Laboratories should be stated here. These methods, as now car- 

 ried out, are as follows: 



1. Preparation of solution: 



100 grammes of true soil (i.e., the field sample sifted through a 3 m.m. sieve; 

 are placed in a flask marked to contain 1,000 c.c. and the flask is filled up to the 

 mark with distilled water and placed in a revolving continuous shaking apparatus 

 for twenty to twenty-four hours. At the expiration of that time the solution is 

 either filtered under pressure through a dry filter placed in a porcelain perforated 

 plate funnel, or, preferably, by means of a Berkefeld candle filter. 



2. Determination of Total Soluble Salts: 



50 c.c. of the above soil solution are evaporated to dryness in a tared platinum 

 dish, ignited at a temperature just below redness, so as to destroy any organie 

 matter present, and weighed. 



5. Determination of Total Carbon Dioxide as Carbonates : 



An aliquot portion of the above soil solution is very cautiously titrated with 

 N/50 sulphuric 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. 



A. Determination of Sodium Chloride: 



To the aliquot portion used in the last determination a few more drops of N/50 

 sulphuric acid are added, then four drops of a chlorine-free Potassium chromate 

 solution, and titratipn is carried on by means of N/100 Silver nitrate, all the 

 chlorine thus determined being calculated as Sodium chloride.* 



5. Determination of Sulphuric Oxide: 



Another aliquot portion of the original soil solution is sightly acidulated by 

 means of hydrochloric acid. If this causes the flocculation of clay, the mixture 

 is filtered and the residue on the filter is 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 

 distilled 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. 



* As a proviso to this the footnote on page 176 should be noted. 



