522 M. Ullgren on the Determination of Carbon in Iron. 



been produced. This is the case when the combustible produces 

 a strong acid, phosphorus for example, in which case the acid 

 formed expels the NO 3 and combines with the ammonia. Schon- 

 bein shows that, when small pieces of phosphorus are burnt in a 

 bell -jar over a plate containing water, the water always con- 

 tains traces of ammonia. He has also found that the combus- 

 tion of arsenic, which takes place at 200° C, is attended with 

 the formation of ammonia, and that the same is the case with 

 the combustion of sulphur. 



Schonbein thinks that in all these cases the combustion of a 

 body produces nitrite of ammonia only in so far that it is a 

 source of heat, and that the process of oxidation in and for 

 itself has nothing to do with the production of the nitrite. He 

 holds in general that nitrite of ammonia is always produced 

 whenever a space containing aqueous vapour and atmospheric 

 air is in any way suitably heated. 



The Messrs. Rogers showed, in 1850, that carbon, even in the 

 difficultly combustible substance graphite, could be oxidized com- 

 pletely by means of a mixture of chromate of potash and sulphuric 

 acid ; and Brunner subsequently improved the method. Ullgren 

 has made a communication* on the subject. The method has 

 the inconvenience that it is difficult to tell when the whole of the 

 carbon is oxidized ; for when strong sulphuric acid and chro- 

 mate of potash are used, as is necessary for graphite, an almost 

 insoluble anhydrous chrome-alum is deposited, which partly 

 prevents the oxidation, and partly prevents any unoxidized par- 

 ticles from being seen. This evil is remedied by using chromic 

 acid instead of chromate of potash. During the operation, too, 

 a large quantity of oxygen gas is disengaged along with the car- 

 bonic acid, and hence it is necessary to pay special attention to 

 the complete absorption of the latter. This is effected in the 

 following manner. About one part of caustic potash is dissolved 

 in four parts of water kept heated at 100°, and pumice in small 

 pieces is added and stirred with it until the whole mass is nearly 

 dry, when it is transferred to stoppered bottles. With this mate- 

 rial the absorption-tubes are filled. It is excellently adapted for 

 the purpose, as it absorbs carbonic acid even when disengaged 

 with extreme rapidity. 



Ullgren gives a description of the apparatus which he uses for 

 effecting the oxidation, for which the original paper must be 

 referred to, where a figure of it is given. Jt consists essentially 

 of a small flask in which the oxidation is effected, of a cylinder 

 containing pumice saturated with sulphuric acid, and also a chlo- 

 ride-of-calcium tube to retain the moisture, and a U-tube con- 



* Liebig's Annalen, October 1862. 



