454 



AGRICULTURAL ANALYSIS 



the solution passes from green to black and at the end the green 

 color is restored. The apparatus employed is shown in Fig. 36. 

 A plain pipette bent as is shown in the figure serves as the 

 generating flask and for the attachment on the one hand to the 

 carbon dioxid apparatus and on the other to the system of ab- 

 sorption bulbs for holding the potassium iodid. The latter 

 should be glass, sealed to the evolution bulb of the pipette to pre- 

 vent the action of the evolved gases on organic materials. The 

 point of the potassium iodid apparatus is drawn out so as to be 

 pushed well into the second receiver, being held in place by a 



Figure 36. Apparatus of Gooch and Gruener. 



piece of rubber tubing. The third receiver acts simply as a trap to 

 exclude the air from the absorption apparatus. The first receiver 

 contains in solution three grams, the second one, and the third a 

 fraction of a gram of potassium iodid for each one tenth of a 

 gram of nitrate used. During the reaction the first re- 

 ceiver is kept cool by immersion in water. Before connecting 

 the apparatus with the carbon dioxid generator the solution of 

 manganous chlorid and afterwards the nitrate solution are drawn 

 into the bulb of the pipette by gentle suction. After connecting 

 the apparatus the current of carbon dioxid is started and kept 

 up until all the air is expelled. Heat is then applied to the 

 bulb of the pipette and the distillation continued until all the 

 liquid has passed over. At the end of the reaction the contents 



