524 M. Ullgren on the Determination of Nitrogen in Iron, 



monia collected and determined in the usual way. The iron was 

 thus found to contain 0*103 per cent, of nitrogen, — a result 

 which agreed very closely with that obtained by determining 

 the ammonia which escaped when the same quantity of the same 

 iron was dissolved in HC1, and by determining that remaining 

 in the liquid. 



To determine the nitrogen which remains in the residual iron 

 graphite when iron has been dissolved, Boussingault has pro- 

 posed its conversion into ammonia by treatment with soda-lime. 

 But this method, as Ullgren found, is not accurate, inasmuch 

 as the temperature at which iron graphite is attacked is above 

 that at which ammonia begins to decompose. Nor were experi- 

 ments more successful which he made to convert the nitrogen 

 into cyanogen by heating the iron graphite with pure carbonate 

 of baryta to a high temperature. He thinks that the nitrogen 

 can only be determined as gas; and the best method he has 

 found is by means of sulphate of mercury. This is well adapted 

 for those carbonaceous substances which do not volatilize or de- 

 compose at an incipient red heat, and it sustains the combustion 

 both with the oxygen of the oxide of mercury and of that of the 

 sulphuric acid, which is thereby reduced to sulphurous acid. 



The execution of the method is briefly as follows : — A com- 

 bustion-tube closed at one end is provided at the other with a 

 delivery-tube which dips under a graduated glass tube receiver. 

 In the posterior end of the tube, either some magnesite or some 

 bicarbonate of soda, which readily part with their carbonic acid, 

 is placed ; after this an asbestos plug, and then the substance 

 mixed with sulphate of mercury and introduced with the usual 

 precautions ; then comes another asbestos plug ; while the rest of 

 the tube is filled with pumice which has been boiled with con- 

 centrated solution of bichromate of potash, allowed to cool, drain, 

 and introduced while still moist. In this condition it completely 

 absorbs sulphurous acid. The other gases are absorbed by means 

 of caustic potash and turmeric. For this purpose the graduated 

 absorption-tube is filled with mercury, inverted over the mercu- 

 rial trough, and some of the solution introduced by a pipette. 



The combustion-tube being placed in a combustion furnace, 

 the posterior end of the tube is heated so as to expel some car- 

 bonic acid ; when the tube is quite full of it, which is determined 

 by obvious methods, the delivery-tube is placed under the ab- 

 sorption-tube, and the part of the combustion-tube containing 

 the substance then rapidly raised to redness and maintained in 

 that state until the disengagement of gas ceases. The rest of 

 the carbonate is then heated until the combustion- and delivery- 

 tube are filled with carbonic acid. The gas is then measured 

 with the usual precautions. 



