120 NEW YORK STATE MUSEUM 



The effect of lime in gravel beds may be noticed when such a 

 deposit is uncovered; for even in dry seasons the pebbles are 

 found in many cases to be covered with a slimy material which 

 on exposure to the air, becomes solid. This in most cases is a 

 salt of lime, usually the bicarbonate, though the sulfate would 

 have much the same effect. A coating of such slimy material has 

 an important chemical action on the pebbles with which it is 

 found, if these be slate, shale or flagstone; for in this case, the 

 lime acts on the potash in these rocks in the same way that it 

 would on the potash in clay. In some soils particles of glauconite 

 or green sand are present, and, as this substance contains an 

 appreciable amount of potash, which in its natural state is only 

 slightly available as plant food, the salts of lime would have an 

 important effect in setting free this potash. 



The amount of moisture retained by a sandy soil where lime 

 salts are not present is nearly if not quite as great as where they 

 are absent, so that the theory that gypsum absorbs moisture and 

 stores it for plant food may be discarded, and the treatment of 

 its action on the constituents of the soil may be taken up undeT 

 the third heading. As a matter of fact, gypsum does not take 

 up water; but as has been stated before, water dissolves gypsum, 

 and, when the w^ater evaporates, the gypsum separates in its 

 former condition. 



The theory noted above, that gypsum gives up part of its 

 oxygen to oTganic substances to promote decomposition, seems 

 to be without foundation, as the experiments of Sir Humphrey 

 Davy show that not the slightest difference in the time of putre- 

 faction can be noted between meat treated with gypsum and that 

 not so treated. That gypsum does absorb ammonia or change it 

 to the sulfate is an unquestioned fact, and it may well be em- 

 ployed about stables as an absorbent of this valuable fertilizer; 

 but that it promotes the formation of ammonia seems to be dis- 

 proved by Davy's experiments. 



The chemical action of gypsum and other salts of lime in set- 

 ting potash free from insoluble compounds is undoubtedly the 

 only tenable explanation of the wonderful results following their 



