68 



AGRICULTURAL CHEMISTRY. 



Organic substances not estimated, con-" 

 taining 12 per cent, of matter insolu- 

 ble in water. Soluable Salts of Iron 

 in small quantity. Water- 



67.7 



32.3 



100.0 



It will be observed from the above analy- 

 sis, that urea does not enter into the compo- 

 sition of guano. The uric acid of the ex- 

 crements must have been decomposed into 

 oxalic acid and ammonia. The soluble sub- 

 stances contained, in guano amount to half 

 its weight. It is singular that we do not 

 find nitrates amongst the ingredients which 

 compose it. Guano possesses a urinous 

 smell, precisely similar to that perceived on 

 the evaporation of urine. The experiments 

 upon the efficacy of this manure in Eng- 

 land have not yet been sufficiently multi- 

 plied to enable us to judge whether or not 

 its virtues have been overrated. 



The corn-fields in China receive no other 

 manure than human excrements. But we 

 cover our fields every year with the seeds of 

 weeds, which from their nature and form 

 pass undigested along with the excrements 

 through animals, without being deprived of 

 their power of germination, and yet it is 

 considered surprising that where they have 

 once flourished, they cannot again be ex- 

 pelled by all our endeavours : we think it 

 very astonishing, while we really sow them 

 ourselves every year. A famous botanist, 

 attached to the Dutch embassy to China, 

 could scarcely find a single plant on the 

 corn-fields of the Chinese, except the corn 

 itself.* 



The urine of horses contains less nitrogen 

 and phosphates than that of man. Accord- 

 ing to Fourcroy and Vauquelin it contains 

 only five per cent, of solid matter, and in 

 that quantity only 0.7 of urea; whilst 100 

 parts of the urine of man contain more than 

 four times as much. 



The urine of a cow is particularly rich 

 in salts of potash ; but according to Rouelle 

 and Brande, it is almost destitute of salts of 

 soda. The urine of swine contains a large 

 quantity of the phosphate of magnesia and 

 ammonia ; and hence it is that concretions 

 of this salt are so frequently found in the 

 urinary bladders of these animals. 



It is evident that if we place the solid or 

 liquid excrements of man or the liquid ex- 

 crements of animals on our land, in equal 

 proportion to the quantity of nitrogen re- 

 moved from it in the form of plants, the 

 sum of this element in the soil must increase 

 every year ; for to the quantity which we 

 thus supply, another portion is added from 

 the atmosphere. The nitrogen which we 

 export as corn and cattle, and which is thus 

 absorbed by large towns, serves only to be- 

 nefit other farms, if we do not replace it. A 

 farm which possesses no pastures, and not 

 fields sufficient for the cultivation of fodder, 



* Ingenhouss on the Nutrition of Plants, page 

 i9 /German edition., 



! requires manure containing nitrogen to be 

 imported from elsewhere, if it is desired to 

 produce a full crop. In large farms, the an- 

 nual expenditure of nitrogen is completely 

 replaced by means of the pastures. 



The only absolute loss of nitrogen, there- 

 fore, is limited to the quantity which man 

 carries with him to his grave ; but this at 

 the utmost cannot amount to more than 3 

 Ibs. for every individual, and is being col- 

 lected during his whole life. Nor is this 

 quantity lost to plants, for it escapes into 

 the atmosphere as ammonia during the pu- 

 trefaction and decay of the body. 



A high degree of culture requires an in- 

 creased supply of manure. With the abun- 

 dance of the manure, the produce in corn 

 and cattle will augment, but must diminish 

 with its deficiency. 



From the preceding remarks it must be 

 evident, that the greatest value should be at- 

 tached to the liquid excrements of man and 

 animals, when a manure is desired which 

 shall supply nitrogen to the soil. The 

 greatest part of a superabundant crop, or, 

 in other words, the increase of growth 

 which is in our power, can be obtained ex 

 clusively by their means. 



When it is considered that with every 

 pound of ammonia which evaporates a loss 

 of 60 Ibs. of corn is sustained, and that 

 with every pound of urine a pound of wheat 

 might be produced, the indifference with 

 which these liquid excrements are regarded 

 is quite incomprehensible. In most place? 

 only the solid excrements impregnated with 

 the liquid are used, and the dunghills con- 

 taining them are protected neither from eva- 

 poration nor from rain. The solid excre- 

 ments contain the insoluble, the liquid all 

 the soluble phosphates, and the latter con- 

 tain likewise all the potash which existed as 

 organic salts in the plants consumed by the 

 animals. 



Fresh bones, wool, hair, hoofs, and horn, 

 are manures containing nitrogen as well as 

 phosphates, and are consequently fit to aid 

 the process of vegetable life. All animal 

 matter is fitted for the same purpose. 

 Butchers' offal, such as the blood and intes-v 

 tines of animals, form a most powerful ma- 

 nure. It is in general necessary to dilute 

 such manure by admixture with other kinds 

 less powerful in their action. 



One hundred parts of dry bones contain 

 from 32 to 33 per cent, of dry gelatine ; now 

 supposing this to contain the same quantity 

 of nitrogen as animal glue, viz., 5.28 per 

 cent., then 100 parts of bones must be con- 

 sidered as equivalent to 250 parts of human 

 urine. 



Bones may be preserved unchanged for 

 thousands of years, in dry or even in moist 

 soils, provided the excess of rain is prevent- 

 ed; as is exemplified by the bones of an- 

 tediluvian animals found in loam or gyp- 

 sum, the interior parts being protected by 

 the exterior from the action of water. But 

 they become warm when reduced to a flue 



