228 Apx)endix 



above. The loss includes organic matter, water not given off at 

 100 C, and carbon dioxide from the carbonates; allowance maj' be 

 made for the latter, but not for the combined water. 



Total nitrogen. Kjeldahl's method is almost invariably adopted. 

 About 25-30 grams of soil are ground up finely in an iron mortar; 

 10-15 grams are then heated in a Kjeldahl flask with 20-25 c.c. 

 of strong sulphuric acid for f hour; then 5 grams of potassium 

 sulphate are added, and shortly after a crystal of copper sulphate. 

 The heating is continued till all the black colour has gone. Then 

 cool and dilute the mixture, transfer the fluid part to a distillation 

 flask, but leave as much as possible of the sand behind, and wash 

 well to remove all the adhering liquid. Add saturated soda solution 

 till the liquid is strongly alkaline, distil and collect the ammonia in 

 standard acid. 



Nitrate. Place 100 grams of soil in a stoppered bottle and shake 

 well with 100 c.c. of water. After waiting for the heavier particles 

 to settle, decant some of the extract through a filter. Evaporate 

 10 c.c. of the filtrate to dryness on a water-bath and add 1 c.c. of 

 phenol sulphonic acid (made by adding 55-5 c.c. of strong pure 

 H2SO4 to 4-5 c.c. of water containing 9 grams of phenol) to the 

 residue, stirring well with a small glass rod. After 10 minutes dilute 

 with 25 c.c. of water and add ammonia or caustic potash till alkaline 

 to litmus paper. If nitrate is present the solution becomes bright 

 yellow, the depth of the colour being proportional to the amount of 

 nitrate. The colour should be compared with that produced by 10 c.c. 

 of a solution of nitrate of soda containing 10 parts of nitrogen per 

 million, i.e., 0-06 gram of the salt per litre. A safety pipette should 

 be used for the phenol sulphonic acid. 



For more accurate work reduce the extract with a zinc-copper 

 couple, distil off the ammonia with standard acid and titrate. 



Carbonates are determined by treating a weighed quantity of the 

 soil with dilute sulphuric acid and estimating the carbon dioxide 

 evolved. Large quantities can be determined rapidly and accurately 

 by Collin's calcimeter (p. 27). Small quantities can be estimated by 

 absorbing the CO2 in potash and determining the amount by titration. 

 Forms of apparatus are described by Amos, Journ. Agric. Science, 

 1905, I. 322-326, Hutchinson and MacLennan, Journ. Agric. Science, 

 1914, VI. 323, and others. 



Mineral substances. Complete analysis of a soil after the" silicates 



