AGRICULTURAL ANALYSIS 



responding to half a gram of the sample, used for each deter- 

 mination. The apparatus employed is shown in Fig. 32. A 

 mixture of five grams of zinc dust and an equal weight of iron 

 filings is employed as the source of hydrogen. The reduction 

 takes place in an alkaline medium secured by adding to the 

 other materials mentioned 80 cubic centimeters of soda-lye of 

 1.30 specific gravity. The respective quantities of iron and 

 zinc may be measured instead of weighed, as exact proportions 

 are not required. After the addition of all the materials the 

 flask is allowed to stand for an hour at room temperature. The 

 distillation is then commenced and continued until at least 100 

 cubic centimeters of distillate have been collected. The receiv- 

 ing flasks are ordinary erlenmeyers, each of which contains 20 



Fig. 32. Halle Nitric Acid Apparatus. 



cubic centimeters of set sulfuric acid, as in the usual kjeldahl 

 process. The receiving flasks are sealed with a few drops of 

 water by the bulb tubes shown in the figure. After the end of 

 the operation the water in each one of the bulb tubes is washed 

 back into its proper flask with freshly boiled water. During the 

 vigorous evolution of hydrogen at the beginning of the operation, 

 some kind of safety arrangement is necessary to prevent the 

 particles of soda-lye being carried over by the bubbles of that gas. 

 The siphon bulb shown in the figure is found effective for this 

 purpose. In this operation better results are obtained by condens- 

 ing the escaping steam, and for this reason. the block tin tubes are 



