368 AGRICULTURAL ANALYSIS 



in order to give a better view of the arrangement of the fur- 

 nace. In the furnace there are three sets of eight digestion flasks. 

 The neck of each flask is held by an opening into a lead tube of 

 five inches diameter, connected with a ventilating flue concealed 

 by the tube in the photograph. Any sulfuric acid which con- 

 denses in this tube is caught by a vessel placed under the lowest 

 part of the lead tube ; the volatile products escape in the flue. 



318. The Distillation Apparatus in Use in the Laboratory of 

 the Bureau of Chemistry. In the nitrogen laboratory of the Bu- 

 reau the distilling apparatus is arranged as shown in Fig. 18. The 

 flasks are the same as are used in the digestion process. They are 

 connected to the block tin condensers by the trap shown in Fig. 19. 

 The block tin condensers are contained in an iron tube through 

 which cold water flows during the distillation. The trap (Fig. 19) 

 above the flask carries an emergent tube which extends to near- 

 ly the center of the trap and is bent laterally to avoid any danger 

 of carrying over any alkali that may be projected into the trap 

 during boiling. A small hole near the bottom allows any con- 

 densed steam to flow back into the distilling flask. The cold 

 water enters the condensers through the pipe provided with a stop- 

 cock shown in the center, and leaves by the two pipes shown at 

 the sides of the apparatus. The boiling is continued usually 

 for nearly an hour, or until bumping begins. The table on 

 which the apparatus is placed is so arranged as to permit of 

 easy access on all sides. The standard acid is held in erlen- 

 meyers placed on wooden blocks so that the end of the con- 

 denser, which is a drawn-out glass tube, dips beneath the surface 

 of the acid. 



319. Patrick's Distilling Flask. To avoid the expense and 

 annoyance attending the breaking of the distilling flasks, Patrick 

 has proposed to make them of copper. 10 The size, about half a 

 liter, made for the evolution of oxygen for experimental pur- 

 poses, may be used. A little excess of potassium sulfid is used 

 tc make up for any of it which might be consumed by the cop- 

 per. About 25 cubic centimeters of this solution are recom- 

 mended. No zinc or pumice stone is required to prevent bumping, 



10 Division of Chemistry, Bulletin 31, 1891 : 142. 



