458 AGRICULTURAL ANALYSIS 



centimeters at a time, from a stock solution of potassium nitrate 

 which contains o.ooooi gram nitrogen, or 0.000045 nitric acid in 

 one cubic centimeter. Each cubic centimeter of this solution, 

 when diluted to 100 cubic centimeters, represents o.oi nitrogen in 

 100,000, and consequently if it is desired to make a solution con- 

 taining 0.35 part nitrogen in 100,000, 35 cubic centimeters are 

 made up to 100 cubic centimeters, and so on. The solution of 

 potassium nitrate (b) is best prepared from a stronger one (a) 

 containing o.oooi gram nitrogen to the cubic centimeter, or 

 0.7214 gram potassium nitrate to the liter; 100 cubic centimeters 

 of (a) made up to one liter give the solution (b). It is obvious 

 that the series of solutions above described could be made directly 

 from (a), but by first making (b) greater accuracy is secured. 



5. For purposes which will be presently described, a solution 

 of aluminum sulfate is required, containing five grams to the 

 liter. The salt used must be free from chlorin and iron ; and the 

 solution should give no reaction when tested with carbazol. 



6. The solution of silver sulfate is required for the removal 

 of chlorin from the water or soil extract to be examined. It is 

 prepared by dissolving 4.3943 grams of the salt in pure distilled 

 water and making up to one liter. The sulfate is preferably 

 obtained by dissolving metallic silver in pure sulfuric acid. The 

 solution should be tested with carbazol in the same way as will be 

 presently described for water; if perfectly pure, no reaction will 

 be obtained. As silver sulfate is often prepared by precipitation 

 from the nitrate, it is very apt to contain nitric acid, and conse- 

 quently, if the source of the salt be unknown, this test should 

 on no account be omitted. The analytical process is carried 

 on as follows: 



Two cubic centimeters of the solution containing the minute 

 quantity of nitric acid are carefully delivered by means of a 

 pipette into the bottom of a test-tube ; four cubic centimeters of 

 sulfuric acid are added, and the solution thoroughly mixed by 

 the help of a glass rod. The test-tube is then immersed in cold 

 water, and when well cooled one cubic centimeter of the sulfuric 

 acid solution of carbazol is added, and the whole again mixed 

 as before. The intensity of the color is observed, and a little 



