CHAPTER XXY. 



THE USE OP CALCAREOUS EARTH RECOMMENDED TO PRESERVE 

 PUTRESCENT MANURES, AND TO PROMOTE CLEANLINESS AND 

 HEALTH. 



THE operation of calcareous earth in enriching barren soils has 

 been, in a former part of this essay, ascribed mainly to the chemi- 

 cal power possessed by that earth of combining with putrescent 

 matters, or with the products of their decomposition ; and in that 

 manner preserving them from waste, for the use of the soil, and 

 for the food of growing plants. That power was exemplified by 

 the details of an experiment (page 95), in which the carcass of an 

 animal was so acted on, and its enriching properties secured. That 

 trial of the putrefaction of animal matter in contact with calcare- 

 ous earth,' was commenced with a view to results very different 

 from those which were obtained. Darwin says that nitrous acid 

 is produced in the process of fermentation, and he supposes the 

 nitrate of lime to be very serviceable to vegetation.* As the 

 nitrous acid is a gas, it must pass off into the air, under ordinary 

 circumstances, as fast as it is formed, and be entirely lost. But as 

 it is strongly attracted by lime, it was supposed that a cover of 

 calcareous earth would arrest it, and form a new combination, 

 which, if not precisely nitrate of lime, would at least be composed 

 of the same elements, though in different proportions. To ascertain 

 whether any such combination had taken place, when the manure 

 was used, a handful of the marl was taken, which had been in im- 

 mediate contact with the carcass, and thrown into a glass of hot 

 water. After remaining half an hour, the fluid was poured off, 

 filtered, and evaporated, and left a considerable proportion of a 

 white soluble salt (supposed eight or ten grains). I could not 

 ascertain its kind ; but it was not deliquescent, and therefore 

 could not have been the nitrate of lime. The spot on which the 

 carcass lay was so strongly impregnated by this salt, that it re- 

 mained bare of vegetation for several years, and until the field was 

 ploughed for cultivation. 



But whatever were the products of decomposition saved by this 

 experiment, the absence of all offensive effluvia throughout the 

 process sufficiently proved that little or nothing was lost, as every 

 atom must be, when flesh putrefies in the open air ] and I presume 

 that a cover of equal thickness of clay, or sand, or any mixture 

 of both, without calcareous earth, would have had very little effect 



* Darwin's Phytologia, pp. 210 and 224. Dublin edition. 

 23 * (269) 



