TECHNIC BACTERIOLOGICAL EXAMINATION OF SOILS. 



291 



aliquots Avere used from the start. The colorimeter shows the depth of color 

 in all bottles made from the 1 cc original aliquot to be about 4-5 of the depth 

 where the 10 cc aliquot was taken at the start. Just as small pebbles form 

 a large part of a small aliquot of soil that may be taken for bacteriological 

 analysis and prevent the results from being representative, the variations in 

 the solid material contained in small aliquots of soil and water mixtures cause 

 a large error in high dilution based on these aliquots. 



To determine whether the differences in color in the above tests might be due 

 to differences in amount of the original soil carried through as part of the 

 aliquots rather than to representativeness of the aliquots under comparison, the 

 bacterial dilutions of two silty loam soils which happened to be at hand were 

 examined. Ten and one cc aliquots of the 1-4, 1-40, and 1-400 1)acterial 

 dilutions were put into tared evaporating dishes, evaporated, dried in the 

 oven at 105°C for two hours, and the residues weighed. The results obtained 

 are given in Table 1. 



Table I. 



Weight of soil in 10 cc and 1 cc aliquots of soil and water mixtures made 

 up by technic under discussion. 



The weight of soil taken in 1 cc from the 1-4 bacterial dilution represents 

 the weight that would be in the 1-400 bacterial dilution providing the bac- 

 terial dilution was increased 100 times at once. 



The weight of soil taken in the 10 cc aliquot from the 1-40 bacterial 

 dilution represents the weight that would be in the 1-400 bacterial dilution 

 providing the bacterial dilution is increased 10 times at the start. 



1 cc aliquots would cause .087 and .111 grams of soil, respectively, to be 



