26 Farmyard Manure. 



straw is gradually changed into these excellent fixers of ammonia, 

 and thus a natural provision is made in dung-heaps to prevent the 

 loss of ammonia. 



Drainings of dung-heaps present us with another interesting 

 chemical particular, which at first sight appears quite anomalous, 

 but which finds a ready explanation in the peculiar composition 

 of these drainings and the properties of humus and ulmic acid. 

 Drainings of dung-heaps, namely, present us with a liquid which, 

 though perfectly neutral to test-paper, may be mixed with a 

 certain quantity of acid without becoming in the slightest degree 

 acid. This will appear from the following experiment : 7000 

 grains of perfectly clear, dark-brown coloured and neutral 

 drainings were mixed with 50 drops of concentrated hydro- 

 chloric acid ; the liquid strongly effervesced, gave off a horrid 

 smell, and deposited a considerable quantity of a brown, flaky 

 substance. The supernatant liquid was much paler, and pro- 

 duced no change on litmus paper. 



A single drop of concentrated hydrochloric acid added to 7000 

 grains of distilled water was readily detected by turning blue 

 litmus paper distinctly red, thus proving that the test-paper was 

 sufficiently delicate to detect the presence of a very small quantity 

 of free acid. 



A further addition of 50 drops of concentrated hydrochloric 

 acid to the same drainings produced a decided acid reaction, 

 and caused the separation of a little more flakulent matter. 



The whole of the brown flaky substance was collected in a 

 weighed filter, dried at 212 Fahr., and weighed, and found to 

 amount to 12*55 grains. 



An imperial gallon of these drainings accordingly contained 

 125*5 grs. of humic and ulmic acids. 



If it be remembered that these organic acids are insoluble in 

 water, and are contained in the drainings in combination with 

 alkalies, the curious circumstance that an acid may be added to 

 neutral drainings without producing an acid reaction will be 

 readily understood. The first quantity of hydrochloric acid had 

 the effect of uniting with the alkalies, and it thus became 

 neutralized, whilst the organic humus acids previously in union 

 with the alkalies of the drainings were separated, and, being 

 insoluble in water, of course could not affect litmus paper. 



I have determined also in the same drainings the amount of 

 carbonic acid which is expelled by simply boiling this liquid, 

 and found in one imperial gallon of drainings 88*20 grains of 

 carbonic acid, which is thus loosely united with the liquid. 



The amount of free ammonia (ammonia expelled on boiling 

 the liquid) in these drainings was determined in the manner 



