8 Morris J. Blish 



ity, and of the same general composition, were used ; but when 

 soils from different localities were used, attempts to arrange them 

 in such a manner were not very satisfactory. For instance, 

 when soils from Lincoln and Weeping Water were compared in 

 this way with soils from Wauneta and McCook, a Lincoln soil 

 containing .5 per cent humus was in no way similar in appearance 

 to a Wauneta soil with the same humus content. This was, no 

 doubt, due to the widely varying amounts of lime and iron in 

 the two types of soil. The same difficulty was experienced in com- 

 paring any of the above mentioned soils with soils from Hold- 

 rege or Hastings. The differences in color were especially marked 

 in the subsoils. Consequently, such a comparison of soils from 

 different localities would be of very little significance, unless one 

 were already very familiar with each soil in all of its characteris- 

 tics. Where the solutions and the colorimeter are used, however, 

 a striking concordance between the colorimetric and the gravi- 

 metric results is generally noticed, excepting in the very weak 

 solutions taken from soils of very low humus content. It is also 

 observed that better results are obtained when the standard is a 

 soil of the same type and locality as the soit under investigation. 



THE PHOTOMETRIC METHOD 



Another method which was tried briefly, and which is especially 

 applicable to soils containing i.oo per cent or more of humus, 

 is the photometric method, which is a modification of the color- 

 imetric method. Li this method it is particularly advisable to use 

 a standard from the same locality as the sample being analyzed. 

 Alway and Pinckney^ did considerable work on this method and 

 describe it as follows : " As a source of light a candle is used, it 

 being placed in a box with a hole, half an inch in diameter, in the 

 top. The candle is held in a clamp 24 inches below the top of the 

 box. Two Hehner cylinders, both of the same internal diameter, 

 are connected by means of a rubber tube, both stopcocks closed 

 and the one cylinder partly filled with the standard solution. 

 The empty cylinder is placed over the opening in the top of the 



3 Agri. Exp. Sta. Uni. of Nebr. 25th Annual Report. 



118 



