96 ON MANURES. 



earths, lime, &c. are present. From the action of car- 

 bonic acid on silicates, both lime and magnesia may 

 change the purple to blue, and during the decomposition 

 which ensues between the sulphate ot" lime which the 

 muck contains and the test itself, lime in its passage from 

 one state to another may affect the test like a free alka- 

 li. Dr. Dana's analysis is doubtless correct. To de- 

 termine whether the muck we used differed essentially 

 from common peat in its fertilizing qualities, two cart 

 loads of what when dry is a light, fibrous peat, were ta- 

 ken directly from the meadow, mixed with ashes in the 

 same proportion as with the other muck, and four rows 

 through the piece of corn, manured therewith. These 

 rows were as good, we thought a little better than the 

 adjoining ones manured with the compost above men- 

 tioned. Since the publication of the paper above men- 

 tioned, two editions of Liebig's Organic Chemistry, in 

 its applications to Agriculture and Physiology, have been 

 published at Cambridge. This is a valuable work for 

 scientific farmers, although some of its theories, not be- 

 ing well established by experiments in the field, should 

 be received with caution. His theory of the operation 

 of plaster of paris is a plausible one, and if correct, of 

 great importance. He says, " the action of gypsum, 

 and chloride of lime really consists in their giving a fixed 

 condition to the nitrogen, or azote, or ammonia, (a com- 

 pound of nitrogen and hydrogen gases,) which is brought 

 into the soil, and which is indispensible for the nutrition 

 of plants." Ammonia is produced by the putrefaction 

 of animal and vegetable substances which contain nitro- 

 gen. Animal manures doubtless owe much of their effi- 

 cacy to this constituent, as those which contain it in the 

 largest proportion are most valuable. Much of the am- 

 monia formed by the process of putrefaction arises and 

 mixes with the atmospheric air. Every shower of rain 

 or snow brings it down again to the earth, and where- 

 ever it meets plaster of paris or chloride of lime, it takes 

 the acids from these salts, and forms with them fixed 

 salts. These, decomposed by the roots of vegetables, 

 famish the nitrogen necessary to their growth. 



