286 PROCEEDINGS OF THE INDIANA ACADEMY OF SCIENCE. 



(1) When tests were made to determine the amount of soil necessary to 

 get rehable cheeks in moisture determination on a silty clay soil, taking 

 aliquots from the sample jars as they came from the field, it was found that 

 it took ten gram aliquots to have the duplicates check regularly to one tenth 

 of one per cent. The soil rarely contained particles o* stone or foreign mattpr 

 that could be picked out and no attempts were made to weigh out exact 

 amounts so we were forced to conclude that to get accurate moisture results 

 ten grams of field soil had to be used. This was when the soil contained 12% 

 to 15% of moisture. Having made the above test, and knowing that the 

 ba3teria which are present in large numbers, are small, and must be dis- 

 tributed in the sample more or less relatively to the internal surface of and 

 the composition of the sample, the authors are forced to conclude that it 

 would take larger aliquots to get good bacteriological results than it would 

 for good moisture results. 



(2) Where the ground is covered with plants and their roots are incor- 

 porated in the surface soil, it is evident that a larger aliquot must be taken 

 to represent the soil. 



(3) When the soil is frozen it is harder to nii.\ the sainples and a large 

 aliquot must be taken to overcome inaccuracies in attempts at mixing. 



(4) A large quantity of soil must be chosen so that the same sized ali- 

 quots of all normal types of soil can be analyzed accurately. This gives a 

 standard. 



(.5) Fifty grams of field soil were cliosen as the ciuantity from whicli to 

 make diluti<ms for the following reasons. Although smaller than the amount 

 used by Dr. Brown it allows the counts made from duplicate and triplicate 

 aliquots from the same field sample to check as well. The results of an ex- 

 tended investigation on size of aliquot of field soil to use will be publish(!d 

 as a separate paper. 



Dilution 



The chemist makes dilutions of various chemical compounds and mix- 

 tures of chemical compounds. To the chemist a s|)ecified dilution is a mix- 

 ture such that all aliquots taken from it by weight (jr l)y volume will be of the 

 same composition. 



Definite amounts of solids are put in solvents and the resulting clear 

 true solutions are exact diluticms of the substances used providing no chemical 

 reaction takes place. Solutions of acids, bases and salts are diluted with 

 water or some other proper solvent and the amounts of materials in the more 

 dilute true solutions bear definite relations by weight and volume to the 

 amounts in the original more concentrated solutions. Definite amounts of 

 a finely divided or ground material are put with definite amounts of another 

 finely divided or ground material and thoroughly mixed. The resulting 

 mixtures are dilutions oi both niiterials because aliquots of mixture have the 

 same composition and the proportions of the original substances contained, 



