1 70 AGRICULTURAL CHEMISTRY 



add 3 cc. ammonium molybdate. The yellow precipitate is am- 

 monium phosphomolybdate. See Experiments 17 and 18. 



220. Sulfur also is an essential element of plant and 

 animal bodies, but occurs in plant tissue in comparatively 

 small amounts. It enters into the composition of albu- 

 min and other proteids. Sulfur is used by plants only 

 in the form of sulfates. The part which it takes in plant 

 life is to supply the sulfur for the proteid compounds 

 which always contain this element in chemical combi- 

 nation. Culture experiments have shown that in its 

 absence no growth results. 



Experiment 44. Sulfur as sulfates in plant ash. To the second 

 portion of the filtrate from Experiment 40 add 2 cc. barium chlorid 

 (BaCl 2 ), observe the result, and write the reaction, assuming SO, 

 to be in the form of K 2 SO 4 . In a second test-tube, add a few 

 crystals of Na 2 SO 4 or K 2 SO 4 to 10 cc. H 2 O containing a few drops 

 HC1. When dissolved add BaCl 2 and compare with precipitate 

 obtained in first part of experiment (see Experiment 21). 



221. Chlorin is not an essential ash element. It accu- 

 mulates mainly in the lower part of the plant, and its pres- 

 ence appears to be accidental, it having no decided func- 

 tions to perform. The statements made about sodium, 

 its occurrence, distribution, and importance apply also 

 to chlorin with which it is combined forming sodium 

 chlorid. 



222. Silicon occurs in all plants. It is found in largest 

 amounts in the dense and older parts, as in the stalk and 

 straw, where there is less activity. In some of the lower 

 plants, as diatoms, there is so much silica that when the 

 organic matter is removed by burning, a skeleton of silica 



