38 
Colorado Experiment Station 
my experiments — I prepared a sample of 3000 pounds and in- 
cubated it out of doors, protecting it from animals, rain and 
from otlier accidents. The moisture content was maintained at 
about 15 percent by addition of ammonia-free water to replace 
that lost by evaporation. The result at the end of 40 days was 
a gain of 36 p.p.m. in total nitrogen, and of 15.79 p.p.m. in 
nitric nitrogen. At the end of this period we applied a dilute 
solution of calcic nitrate to one portion of the surface; to an- 
other portion a dilute solution of sodic nitrate to see if these 
salts would bring about pigmentation. Both of these salts 
brought about a decided change from the ordinary light color 
of the soil to a dark brown, almost black, in a few days. The 
change was distinct in three days. Later in the season the soil 
itself showed this change in spots. This change has been ob- 
served on irrigating furrows in some portions of this land. 
I have expressed elsewhere my conviction that these spots 
are only exceptional manifestations of a general process that 
goes on in our soils with unwonted vigor. 
It may be urged that all this may be true but it does not 
show that these spots actually possess an excessive power of 
fixation in the fields where they are found. In answer to such 
I present the facts shown by the samples collected by Dr. 
Sackett, the most of them in my presence and examined by him. 
It is true that these experiments were strictly laboratory ex- 
periments, but the results of laboratory experiments in these 
lines have yielded results similar to those observed in the field 
and obtained under field or natural conditions. While the ex- 
periments and observations given in the preceding appear to us 
fully adequate for the establishment of all that we have claimed, 
we have endeavored to further ascertain the fixing power of 
samples of soil representing cross-sections of such a nitre-area 
by simply incubating them, adding only enough ammonia-iree 
distilled water to bring the moisture present up to 15 percent. 
The area that we have chosen is in the section of country con- 
sidered in this bulletin. We have had this spot under observa- | 
tion for about three years, during which time it has increased j 
greatly, I would say to at least fifteen times the area that we i 
first observed; and the rate at which it is extending its limits ; 
is much more rapid this season than at any time heretofore. | 
Three years ago there was a very small area that was wholly ^ 
unproductive and none of it was so bad that the owner or lessee | 
did not plant the whole of it. At the present lime no attempt | 
is made to plant several acres of it. Four, perhaps five acres of 
it are now abandoned to such weeds as can tolerate the ])resent j 
