360 AGRICULTURAL ANALYSIS 



has nearly ceased the contents of the flask are brought into gentle 

 ebullition. The boiling is continued until the contents of the 

 flask are colorless, usually about two hours. As a rule, such sub- 

 stances as cottonseed-meal and dried blood will take a longer 

 time for complete combustion than other fertilizing materials. 

 During the combustion the flasks are closed with an oblong loose- 

 fitting unground glass stopper. When the oxidation is finished 

 the contents of the flasks are allowed to cool, the stoppers are re- 

 moved, and enough water is added to fill the flasks about three- 

 quarters full. The flasks are gently shaken, and the possibility of 

 breaking from the heat developed must not be overlooked. To 

 avoid confusion, the flasks are all numbered before beginning the 

 work and the numbers noted by the analyst in connection with 

 the samples. The contents of each one are next poured into the 

 distillation flask and the digestion vessels are washed with 100 

 cubic centimeters of water in three portions and the wash-water 

 added to the liquid. Sometimes in washing out the digestion 

 flask yellow basic mercury compounds separate on its walls, but 

 this does not in any way influence the accuracy of the results. 

 The distillation flasks should have about 600 cubic centimeters 

 capacity. To avoid the transfer, the digestion may take place in 

 the distillation flask, in which case the latter must be made of 

 special glass as indicated. 



To the liquid thus transferred are added 75 cubic centimeters 

 of soda-lye, containing one and one-half times as much potas- 

 sium Ftilfid as is necessary to combine with the mercuric sulfate 

 present. The lye is of such a strength that 60 cubic centimeters 

 are sufficient to neutralize the acid present. It has a specific 

 gravity of 1.375 an< ^ contains 33 grams of potassium sulfid in 

 a liter. 



In order to avoid the bumping which may take place during 

 the distillation, some granulated zinc should be added. 



The distillation flask is closed with a rubber stopper carrying 

 a bulb-tube which ends above in a glass tube about three-quar- 

 ters of a meter long, bent at an acute angle and passing obliquely 

 downward on a convenient support. This tube is connected by a 

 rubber, with the end tube bent nearly at a right angle and dip- 



