232 Appendix 



small crystal of copper sulphate or a globule of mercury to the liquid 

 in the digestion flask. During the process the nitrogen compounds 

 are converted into ammonia, the amount of which is determined by 

 distillation into standard acid after liberation with alkaU, and, where 

 mercury has been used, with the addition also of sodium or potassium 

 sulphide solution. A blank experiment, using 1 gram of pure sugar 

 in place of the sample, is made in order to give the amount of nitrogen 

 present as impurity in the reagents used, which amount must be 

 deducted from the quantity found in the first experiment. 



(6) In presence of nitrates. A weighed sample is put into the 

 K jeldahl flask with 30 c.c. of concentrated sulphuric acid, 1 gram of 

 salicyUc acid is added, and the flask shaken at intervals, but kept 

 cool; then 5 grm. of sodium thiosulphate and 10 grm. of potassium 

 sulphate are put in, and the flask heated till the contents are colour- 

 less or nearly so. The rest of the procedure is as before. 



(c) Nitrogen as ammonia. Alkali is added, and the ammonia is 

 distilled into standard acid as above. 



[d) Nitrogen as nitrates, ammonia and organic nitrogen heinq absent. 

 1 grm. of the sample is placed in a 500 c.c. Erlenmeyer flask with 

 50 c.c. of water. 10 grm. of reduced iron and 20 c.c. of sulphuric acid 

 of 1-35 sp. gr. are added. The flask is closed with a rubber stopper 

 pierced with a thistle tube the head of which is half-filled with glass 

 beads. The hquid is boiled for five minutes and the flask is then 

 removed from the flame, any liquid that may have accumulated 

 among the beads being rinsed back into the flask with water. The 

 solution is boiled for three minutes more, and the beads again 

 washed with a little water. The ammonia is then distiUed off and 

 estimated as before. 



Phosphates, (a) Soluble in water. 20 grm. of the sample are 

 continuously shaken for thirty minutes in a htre flask with 800 c.c. 

 of water. The flask is then filled to the mark, again shaken, and the 

 contents filtered. 50 c.c. of the filtrate are boiled with 20 c.c. of 

 concentrated nitric acid, and the phosphoric acid determined by the 

 molybdate method below. 



(b) Soluble in 2 per cent, citric acid solution. 5 grm. of the sample 

 are put into a stoppered bottle of about 1 litre capacity, and 500 c.c. 

 of a solution of citric acid, containing 10 grm. of the crystallised acid, 

 added. The bottle is shaken in a mechanical shaker for thirty 

 minutes. The solution is then poured all at once on to a large folded 



