37 



4. Coloration of Ammonia Solution. 



The intensity of coloration of the aiunionia extract as an indica- 

 tion of the dej^ree of acidity (33) was tested on only the two upper 

 sections, the smaller amounts of orji;anic matter ])resent in the two 

 lower sections precludino- the use of this method. Twenty grams ol 

 air-dry soil was treated with 250 c.c of 4 per cent ammonia, weU 

 shaken and allowed to stand for ei,e:ht days, when portions were drawn 

 off and compared with a standard solution in a colorimeter. The 

 standard solution was made up from one of the soil extracts which 

 had been drawn off from what appeared to he the darkest in the series. 

 A column of this solution 11.7 cm. high shut out all the lig^ht coming- 

 through an aperture 1 cm. in diameter from a new 25-\vatt Mazda 

 lamp when tested in a dark room. The standard was made by diluting 

 100 cc. of this solution to F^O cc. with distilled water. In comj)aring 

 the test solutions with the standard a column of the former 10 cm. in 

 height was employed and the data reported in tal)les 33 and 34 are the 

 heiglits in centimeters of columns of standard retjuired to exactlv 

 equalize this. All solutions were brown in color, there being none of 

 the black color often obtained in the determination of humus {maticrc 

 noire of Grandeau ). 



On the second day after starting the extraction eight of the solu- 

 tions, ranging in color from dark to light, and representing the differ- 

 ent types, were selected and comparisons with the standard were made 

 daily in order to determine when the increase in depth of color ceased. 

 The results are shown in table 33. Thus, at the time of reading on the 



Tabic JJ. — Prof^ortioiial niiioiiiits of coloring matter cxtrnctcd by amniouia 

 fro)ii day to day. 



sixth da\- it re((uired a higher colunm of standard icj match the dei)th 

 of color in Xos. 1 . 2 and 4 on the Kansan and No. 1 on the Late Wis- 

 consin than it had on the previous day, while in Xo. 3 on the Kansan. 

 and Xos. 2, 3 and 4 on the Late Wisconsin the test showed that no more 

 coloring matter had been extracted during this period. During the 

 seventh dav but little increase in the depth of color occurred. Then all 

 solutions were shaken and on the next day they were compared with 

 the standard. The eight test solutions .showed a slight increase in the 

 depth of color over the previous day. imdoubtcdly due to the last 

 shaking. 



