APPENDIX I 349 



passing contains practically all the nitrates, but it is safer to wash 

 more fully. The solution is poured into a flask covered by an 

 inverted porcelain crucible-lid, lo c.c. of 4 per cent, caustic soda 

 and I or 2 c.c. of 3 per cent, potassium permanganate are 

 added, and the whole is then boiled down to some 75 c.c. and 

 kept just boiling for about two hours. If the permanganate is com- 

 pletely decolorised a little more is added until there is no appreci- 

 able change in half an hour. The excess is then destroyed by 

 cautious addition of sodium sulphite solution and the solution is 

 diluted to 200 c.c. and distilled down to 50 c.c. with the addition 

 of I grm. powdered Devarda alloy, 10 c.c. more of 4 per cent, 

 caustic soda and half a grm. of recently ignited lime. The condenser 

 should be of pure tin with a short length of hard glass tubing at its 

 lower end to dip into the N/50 sulphuric acid in the receiver. 

 Shortly before the end of the distillation the cooling water is emptied 

 out so that steam passes through. A large volume of hydrogen and 

 spray is given off at the beginning of the operation, so special 

 attention must be given to trapping. The titration is carried out as 

 described under Ammonia. 



In the United States the more rapid phenol sulphonic acid 

 method is used. (See C. B. Lipman and L. T. Sharp, Univ. Cal. 

 Pub. Ag. Sci., 191 2, I, 23-37.) 



For statistical discussion of errors see D. D. Waynick, Univ. 

 Cal. Pub. Ag. Sci., 1918, 3, 243-270. 



Ammonia is determined by aeration. The apparatus consists of 

 a glass tube sloping at an angle of about 40° ; its dimensions are 

 about 83 cm. by 2*2 cm. and it has a pear-shaped bulb blown on it 

 at about one-third of its length from the upper end, the small end 

 of the bulb being downwards. It is closed at the lower end by a 

 rubber stopper, through which a glass inlet tube for air passes close 

 to the wall of the larger tube at the under side. The upper end of 

 the large tube is connected by a rubber stopper with a short tube 

 packed with cotton-wool to stop spray, and this in its turn is con- 

 nected with an absorber containing from 5 to 10 c.c. of N/50 

 sulphuric acid diluted with water and a few drops of a 0*05 per cent, 

 solution of methyl red. The freshly taken soil is passed as quickly 

 as possible through a 3 mm. sieve, stones above this size being 

 rejected; 25 grms. are placed at the lower end of the tube on a 

 loose cotton- wool plug, and 50 c.c. of a solution containing 108 

 grms. of sodium carbonate crystals and 150 grms. of sodium chloride 



