96 THE ANALYSIS OF SOILS. V. 



allowed to trickle slowly and with frequent shaking, or better, 

 rotation, into A. The copper sulphate affords a good indica- 

 tion of the amount required. When the solution is alkaline 

 the copper is precipitated as blue copper hydroxide, which, 

 however, is usually quickly converted into black copper oxide 

 owing to the heat evolved by the action of the potash on 

 the sulphuric acid. Care should be exercised, lest frothing 

 takes place during neutralisation. When an excess of potash 

 has been added, the tap of the separating funnel is turned off 

 and steam from B is admitted by connecting with the rubber 

 tube at R. The lamp under A should only have a small flame, 

 lest bumping, due to the presence of the solid matter in the 

 flask, be produced. The flame under B should be of such a 

 size f ;hat the pressure of the steam is sufficient to raise the 

 water in the vertical tube some 8 or 10 inches, due attention 

 being, particularly at first, directed to the prevention of frothing 

 in A. The flask F should be surrounded with cold water in 

 order to condense the steam coming over. This method works 

 very satisfactorily and the ammonia is entirely driven over in 

 about half an hour, and there is little risk of bumping or suck- 

 ing back. 



When the operation is over, the rubber at K is disconnected, 

 the cork loosened from F, E and G are rinsed out by distilled 

 water into F, a little (one or two drops) methyl orange solu- 

 tion added, and decinormal caustic soda solution added from a 

 burette until the red colour just disappears. The amount of 

 ammonia and hence of nitrogen is then easily calculated from 

 the amount of sulphuric acid which has been neutralised by 

 the ammonia carried over in the steam. 



The method gives the nitrogen existing as organic matter 

 and as ammonia in the soil ; it also probably gives some at 

 least of that existing as nitrates, but if nitrates are likely to be 

 present in any considerable quantity about a gramme of salicylic 

 acid or benzoic acid should be added with the sulphuric acid, 

 when nitro-compounds of these acids will be formed, readily 

 capable of reduction to amides and finally to ammonia. 



An example will show the method of calculation. 1O868 

 grammes of soil were treated as described. On distillation into 

 50 c.c. of decinormal sulphuric acid there were required 



