60 



PRACTICE 29 

 Mechanical Analysis. 



Four samples of from five to ten grams of the prepared soil are 

 weighed out and the hygroscopic moisture determined. 



Two of these are then ignited and the percent of loss on ignition 

 is found based upon the water-free soil. Each of the other two sam- 

 ples is placed in a shaker bottle and about 200 cc. of distilled water 

 and from 5 to 10 drops of ammonia are added. The bottles are then 

 placed in the shaker and agitated till a microcopic examination of a 

 drop of the contents shows that the soil particles are completely sep- 

 arated and no granules exist. When this condition is reached, the 

 individual particles will appear clear or semi-transparent in the field 

 of the microscope while any remaining granules will be dark, irregular 

 and opaque. It may be necessary to continue the shaking for twelve 

 or even twenty-four hours tocompletely disintegrate the soil granules. 

 As the determination is quantitive, but a small amount of the liquid 

 is taken from the bottle with a small glass tube and mounted on a slide 

 for examination. When the examination is completed, the slide and 

 cover glass are carefully rinsed with distilled water back into the bot- 

 tle to recover the small portion of soil taken. Great care is necessary 

 throughout the analysis to prevent the loss of any part of the sample, 

 and for purposes of comparison and greater accuracy in results, dupli- 

 cate samples are used. 



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