37 
heat, whereas there was relatively large reduction in the nitrogen of 
the monamino acid group in every soil studied. 
Heating, therefore, caused a loss of nitrogen on the one hand and 
an increase in ammonia on the other, and the decompositions appear 
to come principally from the monamino acid group. The amounts 
of amids in soils Nos. 428 and 447 and the diamino acids in Nos. 406 
and 447 also sustained considerable loss from the heating. 
Regarding that portion of soil nitrogen remaining insoluble in 
hydrochloric acid, next to nothing is known. By again referring 
to the table (p. 35) it will be seen, however, that the heat had some 
effect on the insoluble nitrogen compounds. The difference between 
the total nitrogen in the soil and that extracted shows that consid- 
erable reduction in the insoluble nitrogen of soils Nos. 379 and 447 
took place by heating, while there was a gain in the insoluble nitro- 
gen of soil No. 428. The organic matter of soil No. 428 is in a less 
advanced stage of decomposition than that of the other soils studied 
and it was noticed that a pronounced charring in this soil took 
place under the action of the heat. It seems probable that such 
charring of the organic matter would tend to protect the nitrogen 
bodies in the interior of the particles from the action of the solvent, 
thus apparently increasing the percentage of insoluble nitrogen. 
SUMMARY. 
(1) Twelve different soils representing a wide range of types and 
agricultural conditions were studied with reference to the effects of 
heating to 100° C, to 250° C, and to ignition. The solubility of 
all the mineral constituents except sodium was determined, using 
water and fifth-normal nitric acid as solvents. The effects on the 
nitrogen compounds were also investigated. 
(2) The results showed considerable variation. Neither the abso- 
lute nor the relative solubility of the inorganic constituents were 
effected similarly in all the samples studied. 
(3) On the average, drying at 100° C. was found to bring about 
an increase in the water soluble manganese, lime, magnesia, phos- 
phoric acid, sulphates, and bicarbonates. At this temperature an 
increase in the solubility of potash, silica, and alumina was pro- 
duced in about 50 per cent of the soils examined, but a decrease 
was observed in the solubility of these elements in some instances. 
The solubility of iron was decreased in most instances. 
(4) Heating to 250° C. or ignition produced effects on the solu- 
bility in water similar to those brought about at 100° C, but vary- 
ing in degree, these being sometimes greater, sometimes less in 
intensity than those produced at 100° C. 
(5) The solubility in fifth-normal nitric acid was not greatly 
affected by heating to 100° C, but in some instances heating to 
