MAN 



[ 579 ] 



MAN 



the Use of Salt in Agriculture, by Mr. 

 Cuthbert Johnson. 



Horse-dung evaporated previously to 

 dryness, at a temperature of 100, ab- 

 sorbed during an exposure of three 

 hours to air saturated with moisture 

 at 62, 145 parts ; putrefied tanners' 

 bark, under similar circumstances (66 ), 

 14") parts ; unputrefied tanners' bark, 

 115 parts; cow-dung, 130 parts; pig- 

 dung, 120; sheep-dung, 81; pigeon- 

 dung, 50; refuse marine salt (GO) , 

 49; soot (08), 36; burnt clay, 29; 

 the richest soil (in one hour), 23 ; coal 

 ashes, 14; lime (part carbonate), 11; 

 crushed rock salt, 10 ; gypsum, 9 ; 

 chalk, 4. 



The absorbing power of a manure is 

 much influenced by the state in which 

 it is presented to the atmosphere. In 

 a finely divided state mere capillary 

 attraction assists it ; hence the im- 

 portance of keeping the soil frequently 

 stirred by hoeing, &c. But a mere 

 mass of cotton, by means of capillary 

 attraction, will absorb moisture from 

 the air, yet it parts with it at a very 

 slight elevation of temperature ; it is 

 of importance, therefore, to ascertain 

 which are the manures that not only 

 absorb but retain moisture powerfully. 

 The following results of our experi- 

 ments throw some light on this point : 



Pig-dung evaporated to dryness at a 

 temperature of 106, and then moist- 

 ened with six parts of water, required 

 for being reduced to dryness again, at 

 the above temperature, 135 minutes; 

 horse - dung under similar circum- 

 stances, 90; common salt, 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. 

 The stimulating powers of excrementi- 

 tious manures arise from the salts of 

 ammonia they contain. 



Sir H. Davy found vegetation assisted 

 by solutions of muriate of ammonia 

 (sal-ammoniac), carbonate of ammonia 



(volatile 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. It may be observed, that the 

 nearer any animal approaches to man 

 in the nature of its food, the more fertili- 

 zing is the manure it affords. We have 

 no doubt that a languishing plant one, 

 for example, that has been kept very 

 long with its roots out of the earth, as 

 an orange-tree recently imported from 

 Italy might be most rapidly recovered, 

 if its stem and branches were steeped 

 in a tepid weak solution of carbonate 

 of ammonia ; and when planted, an 

 uncorked phial of the solution were 

 suspended to one of the branches, to 

 impregnate the atmosphere slightly 

 with its stimulating fumes. 



Manures are also of benefit to plants 

 by affording some of the gases of the 

 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, 

 which by a few hours' exposure to the 

 air subsides into a grey or black hue. 

 The first colour appears to arise from 

 the oxide 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 

 gardener may have observed how ra- 

 pidly a blight spade of iron left foul 

 with coal ashes becomes covered with 

 rust, or red oxide. 



Manures assist plants by destroying 

 predatory vermin and weeds. This is 

 not a property of animal and vegetable 

 manures they foster both those ene- 

 mies of our crops. Salt and lime are 

 very efficient destroyers of slugs, snails, 

 grubs, &c. 



Stable manure, and all decomposing 

 animal and vegetable substances, have 

 a tendency to promote the decay of 



