Loess Soils of the Transition Region 7 



the samples, in order to have as complete a comparison as possible 

 of the two methods. However, in reporting the humus content of 

 the transition soils the gravimetric results are used in the case of 

 samples from the first and the second feet, while for those from 

 the third, fourth, fifth and sixth feet, the colorimetric results are 

 employed. The colorimetric method involves simply a compari- 

 son of the color of the solution under investigation with the color 

 of a known standard solution, the solutions being made up in the 

 same manner as the solutions for the gravimetric determination. 

 Alway and Pinckney,- who have previously worked on this method, 

 describe it as follows : " A standard solution of convenient strength 

 is prepared, and an aliquot portion, say 50 c.c, is placed in a 

 Hehner or a Nessler cylinder. This is held beside a similar, but 

 empty, cylinder vertically over a white plate in a good light. To 

 the empty cylinder the humus solution under examination is 

 slowly added until the same tint is observed in both. The results 

 are most accurate when the standard is diluted to such an extent 

 that the diluted solution is of about the same color as the solution 

 under examination." 



From the relative depth of the two solutions and the known 

 strength of the standard, the strength of the unknown solution 

 is readily computed by means of a simple proportion. In this 

 particular work, however, the manipulation was made easier by 

 the use of the " colorimeter," a contrivance in which the two 

 cylinders containing the solutions may be moved up and down 

 until the depth of color is the same in both solutions, the light 

 being reflected up through a wooden chamber from a white 

 glazed paper. The principle is essentially the same, however, in 

 both cases. 



COMPARISON OF THE SOIL COLORS 



Comparisons of the color, of the soils, themselves, both in a 

 wet and in a dry state, were also made. This was done by putting 

 25 gr. samples in shallow porcelain dishes, and attempting to 

 arrange them in order of humus content. This could be done 

 with a fair degree of success where only soils from the same local- 



2 Agri. Exp. Sta. Uni. of Nebr. 25th Annual Report, 1910. 



117 



