CARBON IN ORGANIC SUBSTANCES BY THE KJELDARL METHOD. 753 



the acid must be kept away from any chance of contamination with ammonia or 

 organic matter. 



Example: — 



500 c.c. of Moorfoot water after filtration through sand at the Water "Works, Alnwick Hill. 

 Tube No. 1 contained 2' 9 c.c. carbonic acid. 



,, ,, -j ,, V 4:0 C.C ., 



Total, . . -3 "3 5 c.c ,, 



= 1'8 milligrams carbon. 



200 c.c. distillate containing ammonia. 



Of this, 50 c.c. contained 0'0495 milligrams ammonia. 



0'0495 X 4 = - 198 milligrams ammonia. 

 10 c.c. sulphuric acid contained 0033 „ „ 



Total, . . 0-165 



= - 1358 milligrams organic nitrogen. 



= 0'36 parts per 100,000 organic carbon. 

 = 0'02716 „ ,, „ nitrogen. 



Should nitrates be present in the water in amount more than 1 grain of nitrate of 

 potassium per gallon, these must be got rid of prior to the combustion. After trying 

 several plans, e.g., addition of sulphurous acid, or bisulphite of potassium, to the water 

 during evaporation, the following was adopted as most reliable. From 5 to 10 c.c. of 

 a strong solution of ferrous sulphate (according to the amount of nitrate present) is 

 added to the flask after the water has been evaporated down to 100 c.c.'s, and the 

 evaporation continued as usual. This solution of ferrous sulphate is prepared as follows. 

 Ferrous oxide is precipitated from a strong solution of ordinary ferrous sulphate 

 by means of caustic potash. The precipitated oxide is washed by agitation with boiled 

 and cooled distilled water and decantation until the washings contain no sulphates. The 

 moist oxide is dissolved in the smallest quantity of pure sulphuric acid. This 

 treatment is necessary to free it of ammonia and organic matter. There is still, how- 

 ever, a trace of ammonia in the solution due to the sulphuric acid, and this must 

 be estimated and allowed for. The nitric acid is not decomposed by the ferrous 

 sulphate till the combustion has begun, and the nitric oxide formed, mixing with the 

 air in the apparatus, forms the brown fumes of trioxide and tetroxide of nitrogen. 

 In passing through the watery solution of permanganate of potassium they are 

 decomposed, according to the well-known reaction, into nitrous and nitric acid, which 

 remain in the fluid. 



