MAN 



363 



MAN 



are the manures that not only absorb 

 but retain moisture powerfully. The 

 following results of my experiments 

 throw some light on this point : — 

 Pig dung evaporated to dry-~ 

 ness at a temperature of 

 106°, and then moistened 

 with six parts of water, ^ 135' 

 required for being reduced 

 to dryness again, at the 

 above temperature i 



Horse-dung under similar ) 

 circumstances i 



90 



Common sail 75 



Soot 75 



Rich soil 32 



Chalk 29 



Poor soil (siliceous) .... 23 



Gypsum 18 



These experiments point out a cri- 

 terion by which we easily ascertain the 

 comparative richness of any two given 

 soils or manures ; the most fertile will 

 be most absorbent and retentive. 



Some manures increase the growth 

 and vigour of plants by stimulating their 

 absorbent and assimilating organs. 



which by a few hours' exposure to the 

 air subsides into a gray or black hue. 

 The first colour appears to arise from 

 the oxyde of iron which all soils con- 

 tain, being in the state of the red or 

 protoxide; by absorbing more oxygen 

 during the exposure, it is converted 

 into the black or peroxide. Hence one 

 of the benefits of frequently stirring 

 soils ; the roots of incumbent plants 

 abstract the extra dose of oxygen, and 

 reconvert it to the protoxide. Coal 

 ashes, in common with all carbona- 

 ceous matters, have the power of 

 strongly attracting oxygen. Every gar- 

 dener may have observed how rapidly 

 a bright spade of iron left foul with 

 coal ashes, becomes covered with rust, 

 or red oxide. 



All animal and vegetable manures 

 absorb oxygen from the air during pu- 

 trefaction ? If it be required of what 

 benefit this property is to plants, since 

 the gases are freely presented to them 

 in the atmosphere, it admits the ready 

 answer, that they enjoy the additional 

 quantity which is thus collected to the 



The stimulating powers of excremen- , vicinity of their roots, without the lat- 

 titious manures arise from the salts of ter source being diminished; and that 



ammonia they contain. 



i plants are benefited by such additional 



Sir H. Davy found vegetation assisted , application to their radiculae has been 

 by solutions of muriate of ammonia (sal- , proved by the experiments of Mr. Hill. 



ammoniac), carbonate of ammonia (vol 

 atile salt), and acetate of ammonia. 

 Night soil, one of the most beneficial 

 of manures, surpasses all others in the 

 abundance of its ammoniacal consti- 

 tuents in the proportion of three to one, 



The question may also be asked, 

 whether the roots have the power to 

 extract the oxygen from its combina- 

 tion ? That they have this power ad- 

 mits of little doubt, since Saussure 

 found that they were able to extract 



It may be observed, that the nearer j various saline bodies from their combi- 

 any animal approaches to man in the ' nations ; not only extracting but select- 

 nature of its food, the more fertilizing ing in those cases where several salts 



is the manure it affords. 



I have no doubt that a languishing I 



were in the same solution. 



Dr. Daubeny, the Oxford professor of 



plant, one, for example, that has been I agriculture, has also shown that stron- 

 kept very long with its roots out of the ' tian is rejected by barley, pelargoniums, 

 earth, as an orange tree recently im- and the winged pea. 

 ported from Italy, might be most rapid- [ Carbonic acid is also of benefit to 

 iy recovered, if its stem and branches plants, when applied to their roots in 

 were steeped in a tepid weak solution an advanced stage of their growth. 

 of carbonate of ammonia, and when [ Animal and vegetable matters evolve 

 planted, an uncorked phial of the so.- this gas whilst putrefying ; and I am 

 lution were suspended to one of the ' not aware of any manure that absorbs 

 branches, to impregnate the atmosphere it from the atmosphere, so as to be for 



slightly with its stimulating fumes. 



that reason beneficial to vegetation. 



Manures are also of benefit to plants 1 Lime attracts it rapidly, but combines 

 by affording some of the gases of the I with it so strongly that it is useless to 



atmosphere to their roots in a concen 

 trated form. A soil, when first turned 

 up by the spade or plough, has gene- 

 rally a red tint, of various intensity. 



the plant, until the carbonate of lime 

 so formed is imbibed and elaborated. 



Manures assist plants by destroying 

 predatory vermin and weeds. This is 



