TECHNIC BACTERIOLOGICAL EXAMINATION OF SOILS. 



293 



4. That the increased concentration of the soil in the soil and water 

 mixtures increases the amount of soil taken in succeeding 10 cc aliquots. 



5. That per cc of aliquot taken the 10 ec aliquots contain nearer con- 

 stant amounts of a given soil in spite of 4. 



The experiments to this point having shown that a ten cc aliquot is more 

 representative of a soil and water mixture than a 1 cc aliquot the following 

 determinations and calculations were made to find out if, in following regular 

 systems of dilution, the soil making up part of a 10 cc aliquot would cause 

 more or less departure from the bacterial dilution desired than the soil making 

 up part of the 1 cc aliquot would. 



In addition to using the determinations of the soil in the 10 cc and 1 cc 

 aliquots already given, the results from five more soils were also secured. 

 All determinations used as the basis of calculations are given in Table III. 

 The soil in the first 10 or 1 cc aliquot taken is used as this would be the aliquot 

 used in making bacterial dilutions. 



Table IV shows the dilutions that actually would be made if uniform 

 systems of dilution were employed. A 1 cc aliquot would be put in practice, 

 with 9 cc of water and a 10 cc aliquot with 90 cc of water to increase the 

 dilution ten times. 



Table IV. 



Actual bacterial dilutions made with 10 cc and 1 cc aliquots of 1-4 bac- 

 terial dilutions of ten soils. 



Column headings denote bacterial dilutions desired. 



*Samples very finely divided and dry. 



