24 Farmyard Manure. 



contained in drainings of dung-heaps, partly in mechanical solu- 

 tion, but chiefly in the form of bi-carbonates ; these, on boiling, 

 are decomposed into neutral carbonates, and into carbonic acid, 

 which escapes. 



On addition of hydrochloric acid the liquid strongly effervesced 

 and gave off a most disgusting stench. Notwithstanding the 

 disagreeable odour produced, on adding hydrochloric acid to 

 these drainings of a dung-heap, there was no sulphuretted hydro- 

 gen in the mixed gases which escaped. The acidulated liquid 

 being heated deposited in abundance a dark brown flaky sub- 

 stance, which was afterwards identified as a mixture of humic 

 and ulmic acids. The deposition of these organic acids in the 

 shape of a brown flaky mass had the effect of leaving the super- 

 natant liquid merely pale yellow. It is thus plain that the dark 

 brown colour of drainings of dung-heaps is due to compounds of 

 humic and ulmic acids. These compounds are easily decom- 

 posed by mineral acids, and as the dark-coloured organic acids, 

 which separate, in a free state are nearly insoluble in water, the 

 original dark brown liquid is decolourized. 



Humic and ulmic acid are both products of the decay of car- 

 bonaceous organic matters, and their abundance in the drainings 

 of dung-heaps is easily explained by the decomposition of the 

 straw and the non-nitrogenized constituents of excrementitious 

 matters. In combination with potash, soda, and ammonia, 

 humic and ulmic acids form dark -coloured, readily-soluble salts ; 

 whilst with lime, magnesia, and earthy and metallic bases the 

 same organic acids form compounds insoluble in water. 



The dark brown colour of the drainings therefore is an indirect 

 proof of the existence in them of potash, soda, or ammonia. The 

 subsequent examination indeed has afforded the direct proof that 

 drainings of dung-heaps contain all three alkalies, combined at 

 least in part with organic acids, which being found in large quan- 

 tities in humus may be called by the generic name of humus- 

 acids. 



Chemists are well acquainted with the fact that with the 

 degree of heat to which chemical agents are exposed their 

 affinities "one towards the other are changed. Thus, for instance, 

 at the ordinary temperature of the atmosphere, or at the heat of 

 boiling water, sulphuric acid is capable of separating phosphoric 

 acid from bone-earth, and forming with the lime of the latter 

 sulphate of lime or gypsum. But when a mixture of sulphate of 

 lime and phosphoric acid is heated to redness, the affinities 

 between lime and phosphoric and sulphuric acid are changed. 

 A reverse action to that which takes place at a comparatively low 

 temperature manifests itself, and, provided the temperature is 

 sufficiently elevated and enough phosphoric acid present, all 



