THE HYDROGEN METHOD 34! 



During the combustion the end of the tube projecting from 

 the furnace must be kept heated sufficiently to prevent the con- 

 densation of moisture, yet not enough to char the stopper. The 

 heat may be regulated by a shield of tin slipped over the pro- 

 jecting end of the combustion tube. 



It is found very advantageous to attach a bunsen valve to the 

 exit tube, allowing the evolved gases to pass out freely, but pre- 

 venting a violent sucking back in case of a sudden condensation 

 of steam in the bulbs. 



300. The Official French. Method. The French chemists pre- 

 fer to drive out the traces of ammonia remaining in the com- 

 bustion tube by means of the gases arising from the decomposi- 

 tion of oxalic acid. 88 The operation is conducted by mixing 

 about one gram of oxalic acid with enough of dry granular soda- 

 lime to form a layer of four centimeters in length at the bottom 

 of the tube. The rest of the tube is then charged substantially 

 as directed above. At the end of the combustion, the oxalic ax:id 

 is decomposed by heat, furnishing sufficient hydrogen to remove 

 from the tube all traces of ammonia which it may contain. The 

 French chemists employ for titration, either normal acids and 

 alkalies or some decimal thereof, or else an acid of such strength 

 as to have each cubic centimeter thereof correspond to 10 milli- 

 grams of nitrogen, thus making the computation of results ex- 

 ceedingly simple. Such an acid is secured when one liter thereof 

 contains 35 grams of pure monohydric sulfuric acid or 45 grams 

 of pure crystallized oxalic acid. The corresponding alkaline re- 

 agent should contain, in each liter, 40 grams of pure potassium 

 hydroxid. 



301. The Hydrogen Method. Thibault and Wagner recom- 

 mend that the combustion with soda-lime be conducted in an at- 

 mosphere of hydrogen ; and Loges replaces this by common 

 illuminating gas freed from ammonia by conducting it through 

 a tube filled with glass balls moistened with dilute sulfuric 

 acid 89 - 90 . 



In these cases the combustion tube is left open at both ends 



88 Grandeau, Trait d' Analyse des Matieres agricoles, 3me Edition, 

 1897, 1 : 427. 



89 Zeitschrift fur analytische Chemie, 1884, 23 : 557. 



90 Chemiker-Zeitung, 1884, 8 : 649, 1741. 



