PROGRESS IN BIOLOGICAL INQUIRIES, 1926 545 
from pH 7 to pH 9.2. In the deeper lakes the bottom water usually 
gave lower readings than the surface water; in Trout Lake, for 
example, the range was from pH 7.6 at the surface to pH 6.6 at 
the bottom (32 meters). 
The surface stratum in these lakes was well supplied with dissolved 
oxygen; the amount varied from 4 cubic centimeters to a little 
more than 7 cubic centimeters per liter. In some of the deeper lakes 
the lower water possessed very little or no dissolved oxygen at all. 
The quantity of free ammonia in the surface water ranged from 
a minimum of 0.016 to a maximum of 0.68 milligram per liter of 
water. In lakes having a depth of 5 meters or more, the lower water 
usually contained a larger amouit of free ammonia than the upper. 
In Lake Mary, on July 12, 1926, the surface water yielded 0.024 
milligram of free ammonia per liter, and the bottom water (20 
meters) 2.40 milligrams, or a hundred times as much as the surface. 
In inost instances, however, the bottom water vielded mot more that 
5 to 10: times as much as the surface. 
The amount of combined or organic nitrogen in the surface water 
varied from a minimum ef 9.073 milligram per liter to a maximum 
of 0.88 milligram. The quantity of organic nitrogen depends chiefly 
npen the amount of plankton that is present. In some of the deeper 
lakes a larger amount of organic nitrogen was found in the lower 
than in the upper water, but the reverse was true in the majority 
of these lakes. 
Most of the lakes contained no nitrite nitrogen, or only a trace; 
a few yielded measurable amounts of nitrite, the amount varying 
from 0.001 to 0.01 milligram per liter. Similar results were ob- 
tained for the nitrate nitrogen, but as much as 0.08 milligram per 
liter was noted in the bottom water of Trout Lake on August 14. 
In only a few instances did the nitrate nitrogen exceed 0.02 milli- 
gram per liter, and only a trace or none at all was found in the great 
majority of the samples. 
The 1926 observations included the organic phosphorus as well 
as the soluble; only the latter was determined in 1925. No soluble 
phosphorus was found in the upper water of one lake and only a 
trace in another; in all of the other lakes the amount in the upper 
water varied from a minimum of 0.003 to a maximum of 0.015 milli- 
gram per liter. In many instances the soluble phosphorus was uni- 
formly distributed from surface to bottom, but in others there was 
a more or less marked increase in the lower water. In Lake Mary 
there was no soluble phosphorus at the surface and at 3 meters, but 
0.75 milligram per liter of water at 20 meters on July 12, 1926. 
The quantity of organic phosphorus in the upper water varied 
from a minimum of 0.01 to a maximum of 0.05 milligram per liter, 
but it exceeded 0.04 milligram in only three lakes. In most of the 
lakes the upper water contained from two to four times as much 
organic phosphorus as soluble phosphorus. In some of the lakes the 
organic phosphorus was substantially the same from surface to bot- 
tom, but in others the lower water contained from two to four times 
as much as the upper. 
The silica varied from only a trace or none at all to a maximum 
of 10 milligrams per liter in one lake. In most instances, however, 
66552—28——3 
