16 Farmyard Manure. 



by this gentleman that his disinfecting powder possesses the 

 property of fixing ammonia in dung, and thereby rendering it 

 more valuable than manure made in the ordinary manner. 

 . According to the published accounts, M'Dougall's powder 

 consists chiefly of sulphite of lime and sulphite of magnesia, and 

 contains also some carbolic acid in combination with lime, and 

 free lime. It is said to be prepared by passing sulphurous acid 

 into slaked lime, obtained on burning magnesian limestones, and 

 by mixing with this product a certain quantity of crude carbolic 

 acid, probably in the state of gas-tar. 



The theory of the action of this disinfecting powder is described 

 by the inventor in the following words : 



" The only agent we know which will decompose the noxious emanations 

 from putrescent excreta, or other animal offal, without creating any detri- 

 mental action upon those elements which we wish to preserve, is sulphurous 

 acid. 



" Let us take two atoms of sulphuretted hydrogen, and one of sulphurous 

 acid ; when they are brought into contact, they are mutually decomposed, 

 and form three of sulphur and two of water, both of which are entirely odour- 

 less. A similar reaction will ensue if we put phosphoretted hydrogen in the 

 place of sulphuretted hydrogen, only the products would be two of phos- 

 phorus, one of sulphur, and two of water as before, both of which are also 

 entirely odourless. 



" Here, then, we have the means of solving the first condition of the pro- 

 blem. By the agency of sulphurous acid the offensive smell of putrescent 

 substances may be removed. Further than this, sulphurous acid has a 

 conservative action, which is highly favourable to our object. It has a strong 

 affinity for oxygen, and will not permit other substances in its presence to 

 combine with oxygen till its own affinity is satisfied. It thus exercises an 

 influence highly anti-putrescent, besides decomposing the offensive compounds 

 which have been already formed. 



" We have another guarantee, however, for the prevention of putrefactive 

 fermentation ; this is the carbolic acid, which has the property of coagulating 

 albuminous substances, and generally of preventing putrescence. As it is a 

 liquid oily compound, we combine it with lime, and are thus enabled to dry 

 it and reduce it to a powder, so rendering its application easy and simple. 



" It only remains now that I explain the reason why we use magnesia in 

 combination with the sulphurous acid. The reason is, that the compounds to 

 be preserved are ammonia and phosphoric acid, and magnesia is the only 

 available element which combines with them both and forms a triple com- 

 pound, perhaps of all other possible combinations the best for agricultural pur- 

 poses, viz. the triple phosphate of magnesia and ammonia. 



" In the treatment of sewage or other similar matter in an advanced stage 

 of decomposition, containing any considerable percentage of ammonia, we find 

 it advantageous to add a soluble phosphate, as the quantity of phosphoric acid 

 in the substances to be operated upon is not, in the circumstances, sufficient to 

 permit the formation of the triple phosphate. 



" Thus, then, we use sulphurous acid to remove the offensive smell, car- 

 bolic acid to prevent putrefactive fermentation, a little lime to neutralize and 

 dry this latter acid, and magnesia to combine with and preserve the phosphoric 

 acid and ammonia ; and, in special cases, we add a soluble phosphate to pre- 

 vent the loss of any of the ammonia." 



