88 T. Lyttleton Lyon and James A. Bizzell 



METHODS FOR THE CHEMICAL ANALYSIS OF CROPS 



Preparation of sample. — The air-dry sample was ground to a fineness 

 sufficient for passing thru a sieve having circular perforations 1 miUimeter 

 in diameter, and then thoroly mixed. 



Moisture. — A convenient quantity of the sample (from 2 to 5 grams) 

 was dried at the temperature of boiling water for five hours. The loss 

 in weight was considered as moisture content 



Nitrogen. — Nitrogen was determined by the official Gunning method 

 described in Bulletin 107 (revised) of the United States Bureau of 

 Chemistry, page 7, with the following slight modification. Approximately 

 1 gram of copper sulfate was added to the Kjeldahl flask at the beginning 

 of the digestion. 



Phosphorus. — The method of making the solution for determining the 

 phosphorus content of the crops was as follows. Two grams of the sample 

 ■was placed in a platinum dish and mixed with 5 cubic centimeters of 

 magnesium nitrate solution The mixture was then dried, ignited, and 

 dissolved in hydrochloric acid. 



The determination of phosphorus was made by the optional volumetric 

 method described in Bulletin 107 (revised) of the United States Bureau 

 of Chemistiy, page 4, 



Sulfur. — The provisional peroxide method, described on page 23 of 

 the bulletin cited above, was used for determining the sulfur content. 



Ash. — To determine the ash content, 10 grams of the sample was 

 placed in a platinum dish, and the whole was placed in a graphite muffle 

 and heated gently until the volatile matter was expelled. The heat 

 was then raised to just below redness and this temperature was maintained 

 for several hours. The contents of the dish were then extracted wdth 

 distilled water and the insoluble residue was dried and incinerated until 

 it was white. The aqueous extract was then evaporated and added to 

 the ash. 



Calcium, magnesium, potassium, and sodium. — To determine the 

 calcium, magnesium, potassium, and sodium content, the ash, prepared 

 as described above, was transferred to a beaker or an evaporating dish 

 and dissolved in hydrochloric acid. This was evaporated to complete 

 dryness, to render the silica insoluble. The residue was moistened with 

 from 5 to 10 cubic centimeters of hydrochloric acid, 50 cubic centimeters 

 of water being added, allowed to stand on the water bath for a few minutes, 



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