METHOD OF SCHMITT 443 



and the volume of gas evolved noted and reduced by the usual 

 tables to o and 760 millimeters pressure of the barometer. 



An amalgam prepared as above gives about three cubic centi- 

 meters of hydrogen for each gram. The thimble holds from 12 

 to 15 grams. 



The estimation of nitric acid is made in a solution containing 

 about one-tenth per cent, of nitrate. Ten cubic centimeters are 

 used, to which six-tenths gram of tartaric acid is added, and placed 

 in the outer part of the glass stopper. The rest of the process is 

 conducted exactly as described above. The deficit in hydrogen 

 is calculated to nitrogen pentoxid. 



The reduction by sodium amalgam is not so convenient a form 

 of estimating nitric acid as many of the other forms of using 

 nascent hydrogen. As practiced by calculating from the deficit 

 of hydrogen, however, it has some advantages by reason of the 

 fact that no heating is required. The presence of organic neu- 

 tral bodies, or even those of an acid nature, like humus, does not, 

 therefore, interfere with the work. Likewise, mineral bodies 

 in solution, which are not reduced by nascent hydrogen, do not 

 interfere with the accuracy of the reaction. 



382. Method of Schmitt. In the method of Schmitt 40 cubic 

 centimeters of glacial acetic acid are placed in a flask of 600 cubic 

 centimeters content, and 15 grams of a mixture of zinc and iron 

 dust added. 65 To this quantity of the solution containing the 

 nitrate, representing about half a gram of the pure nitrate, is added 

 with constant shaking, in portions which do not evolve hydrogen 

 too rapidly. After about 15 minutes when the evolution of hydro- 

 gen has somewhat diminished, an additional 15 grams of the 

 metal dust are added. If the contents of the flask become thick 

 they are diluted with water. The reduction is complete in from 

 30 to 40 minutes. The contents of the flask are saturated with 

 enough soda-lye not only to neutralize the excess of acetic acid, 

 but to keep the zinc hydroxid also in solution. For this purpose 

 about 200 cubic centimeters of soda-lye of 1.25 specific gravity are 

 necessary. The ammonia is obtained by distillation into standard 

 acid in the usual way. 



65 Chemiker-Zeitung, 1890, 14 : 1410. 



