PREPARATION OF REAGENTS 353 



portion of the body and neck is kept sufficiently warm to prevent 

 the sulfuric acid fumes from condensing and flowing back into 

 the retort. Both these ends are attained by surrounding the re- 

 tort with a piece of sheet iron, cylinder-shaped beneath, and with 

 an oval upper part, having an opening of about one centimeter 

 in diameter for the neck of the retort. To conduct the distilla- 

 tion, a burner is used with an arrangement for spreading the 

 flame. To avoid with certainty all bumping of the sulfuric acid 

 and the resulting danger therefrom, the lamp is so arranged that 

 only the products of combustion go up between the retort and 

 its iron hood, without allowing the flame itself to come into con- 

 tact with the glass vessel. The retort should be filled about half 

 full, or with 200 cubic centimeters of acid. By this device, with- 

 out any danger whatever, about one liter of sulfuric acid may 

 be distilled in a day. The retort will stand numerous distilla- 

 tions. Once begun, the distillation takes care of itself ; it is neces- 

 sary to discontinue it when only the bottom of the retort is cov- 

 ered with sulfuric acid, and to fill with fresh acid through a funnel 

 when the retort has cooled off. The first 20 cubic centimeters 

 of the distillate going over are collected by themselves and re- 

 jected. What comes over later is, as shown by experience, ab- 

 solutely ammonia-free, and can be used without any correction 

 for the nitrogen determinations according to Kjeldahl. The acid 

 is kept in a stoppered bottle in a place not reached by ammonia 

 fumes. The 10 cubic centimeter pipette used for measuring the 

 quantity of sulfuric acid required for each determination is fast- 

 ened in the perforated rubber stopper with which the bottle is 

 kept closed, and is itself closed above by a small rubber tube 

 with a plug of glass wool in it. 



(2) Potassium Permanganate. Crystals of this salt are crushed 

 (not pulverized) with a pestle into small pieces of about one- 

 half millimeter size, which are kept in a long glass tube of about 

 ten millimeters diameter, closed with a stopper. 



(3) Ammonia-free Water. Common distilled water can not be 

 used in the determination of nitrogen according to Kjeldahl, since 

 it contains ammonia. Water may be obtained free from ammonia 



12 



