128 Farmyard Manure. 



inserted. At the same time an equal quantity of rotten dung 

 was put into a second bottle, and some of M'Dougall's pow- 

 der was well mixed with the dung. The animal smell, as before, 

 was completely removed. In the neck of the second bottle a 

 red litmus paper was inserted. In the course of a few minutes 

 the litmus paper in contact with the air surrounding the deodo- 

 rized dung was distinctly turned blue, whilst the paper in the first 

 bottle retained its original red colour, thus proving clearly that 

 the dung which contains no free ammonia, when deodorized 

 with M'Dougall's powder, gives oif ammonia in a perceptible 

 degree. 



I have shown in numerous experiments" that the amount of 

 ammonia wliich may be obtained by treating farmyard manure 

 with quick lime is but small ; unmixed with any other animal 

 emanations, when gradually liberated by a powder Avhich, like 

 M'Dougall's, contains only little caustic lime, and masked by the 

 smell of tar, the ammonia in dung is hardly perceptible by the 

 smell. And as many people refer the smell of dung to ammonia, 

 forgetting that the peculiar putrescent smell of dung is princi- 

 pally due to other animal exhalations, I can readily understand 

 the mistaken idea which no doubt many entertain who have 

 practically tested the effects of this disinfecting powder upon 

 dung. But let them try the effect of M'Dougall's powder upon 

 a solution of sal-ammoniac or sulphate of ammonia, and they will 

 find, without difficulty, that it liberates from these inodorous 

 salts the pungent-smelling ammonia. Or, by mixing a moderate 

 quantity of the powder with a manure which, like guano, contains 

 a large proportion of ammoniacal salts, it may be shown tliat 

 M'Dougall's powder contains a constituent, the chemical effect 

 of which manifests itself by the copious discharge of ammonia. 



?)rd Set of Experiments. 



In a third series of experiments I have studied the disinfecting 

 properties of M'Dougall's powder in relation to liquid manure. 



With a view of ascertaining what share the sulphite of mag- 

 nesia and sulphite of lime had in the deodorizing effect upon 

 liquid manure, and what share the free lime contained in the 

 powder, I prepared a pure and concentrated solution of sulphite 

 of lime and sulphite of magnesia, the effects of which were tried 

 upon liquid manure. 



For other experiments I used a solution of gas-lime, prepared 

 as described above, and I also tried the effects of slaked lime 

 mixed with some coal-tar. 



Finally, I saturated the free lime in M'Dougall's powder, by 

 passing into it sulphurous acid as long as it was absorbed, and 



