TRANSACTIONS OF CHAMPAIGN CO. HORTICULTURAL SOCIETY. 245 



3rd, That in some way the nitrous acid of a soil is iminiateiy connected with vege- 

 table growth ; that, therefore, those conditions most favorable to its production arc, 

 other things being equal, just the conditions most favorable to growth. Hence we find 

 the season of most luxuriant vegetation is coincident with that of the most abundant for- 

 mation of nitrous acid. It is when, by alternate showers and sunshine, the soil is con- 

 stantly passing from the moist to the dry state, that the processes of nitrification and veg- 

 etation alike go on most vigorously. 



4th, We see how the mechanical condition of a soil is related to growth. To dry 

 rapidly after it has been wet by a shower, a soil must be porous ; for when compact, even 

 though supplied with all the solid constituents necessaiy for growth, it neither receives 

 nor parts with moisture readily, and therefore gives rise to but little nitrous acid. 



Such are the inferences of Jeannel. 



These experiments have suggested several important questions, which we have en- 

 deavored to study, and to which we now beg leave to invite your attention. 



1st. What is the true cause of nitrous acid in a soil, or rather is it due to one or to 

 several similar causes ? If we wash ]3ure silicious sand with pure water, and nearly dry 

 it, we find by farther washing no nitrous acid. If we mix with such sand some pure 

 pulverized marble, and repeat the jirocess, we obtain nitrous acid. If we now take pure 

 pulverized marble alone, and proceed as before, we obtain again nitrous acid. This 

 teaches us that limestone is one thing, at least, in a soil capable of producing nitrous acid. 

 In some way it has, while drying, the power of changing the chemical combination of the 

 oxygen, nitrogen, and water in the interstices of the limestone to nitrous acid. This 

 acid, under proper conditions, readily passes into nitric acid ; and hence is explained the 

 occurrence of nitre in caves of limestone districts — as for instance in the mammoth cave. 

 The walls of the cave are alternately moist and nearly dry, from the intermittent (low of 

 water thrciugh the crevices above, and are therefore in just the condition to produce ni- 

 trous acid. Hence the accumulation of nitre in caves of limestone, or rather of calcium 

 nitrate, from which common nitre is, in such cases, prepared. 



But is limestone the only substance capable of producing nitrous acid ? Three 

 other substances have properties very similar to those of lime, viz., baiyta, strontia, and 

 magnesia; and the thought was natural, that these substances might also act in a similar 

 manner. Experiment teaches that they do act in a similar maimer, although not, per- 

 haps, in eveiy instance quite so energetically. For instance, a mixture of pure sand and 

 barium carbonate, washed until it gave no reaction for nitrous acid, and left three days, 

 gave, on washing again, distinct indications of nitrous acid. A mixture of pure sand 

 and magnesium carbonate, treated in the same way, gave feeble indications of nitrous 

 acid. A mixture of pure sand and strontium carbonate, washed in like manner, gave 

 .ilso feeble indications of nitrous acid. Similar experiments made with tire-clay and 

 sand, also with sesquioxide of iron and sand, seemed to show a trace of nitrous acid ; but 

 further experiments are necessary to ascertain the exact truth in these cases. It appears, 

 then, that not only limestone, but several other substances, under similar conditions, have 

 the power of i)ro<]ucing nitrous acid. As some of these substances, particularly baryta 

 .xnd strontia, arc comparatively rare, their agency in nitrification must be correspondingly 

 small. 



It should be added that moderately high temperatures, and free access of air, arc 

 indispensible conditions in the formation of nitrous acid. Each of the mixtures above- 

 mentioned, when washed clean and allowed to stand twenty-four hours at a temperature 

 near the freezing point, showed no sign of nitrous acid. We learn from this the condi- 

 tion of our soils during the frosty months of the year, and how a cold season, moreover, 

 is ill suited to produce abundant crops. 



Another question suggested by the study of this subject is, does calcium sulphate, 

 or gypsum, act in this respect like the carbonate ? So far as ex])eriment teaches, gypsum, 

 washed and nearly dried, does produce nitrous acid, although apparently in smaller 

 (|uantity than that produced by the carbonate. If this be so, it suggests a new theory of 

 the action of gypsum in fertilizing soils, viz., its inlluence in forming nitrous acid. It will 

 be remembered that one of the most important theories of the action of gypsum in fertiliz- 

 ing soils, is its fixation of the ammonia of the atmosphere and of the soil as sulphate o 



