142 MANUFACTURE OF FERTILIZING MATERIALS 



following scheme for soil analysis it is in- 

 tended to use the air-dried soil from the sample 

 bottle for each separate investigation. The de- 

 termination of moisture, made once for all on 

 a separate portion of air-dried soil, will afford 

 the datum for calculating the results of analysis 

 upon the soil dried at the temperature of boil- 

 ing water. It is not desirable to ignite the soil 

 before analysis, or to heat it so as to change 

 its chemical properties. 



The acid digestion is to be performed in a 

 flask so arranged that evaporation of acid shall 

 be reduced to a minimum, but under atmos- 

 pheric pressure and at the temperature of boil- 

 ing water. The digestion is easily accomplished 

 in a flat-bottom conical flask of hard glass, Car- 

 rying a stopper and hard-glass condensing tube 

 at least 18 in. long. Where sulphuric acid is 

 to be determined a rubber stopper cannot be 

 used. A flask with ground-glass stopper, carrying 

 a condensing tube, is useful in such cases. 



The flask must be immersed in the water- 

 bath up to the neck, or at least to the level of 

 the acid, and the water must be kept boiling 

 continuously during the digestion. 



In the following scheme 10 gms. of soil are 

 used, this being a convenient quantity of most 

 soils, in which the insoluble matter is about 

 80 per cent. If desired, a larger quantity of 

 such soil may be used, with a proportionately 

 larger quantity of acid, and making up the soil 



