XII.] Loss OF NITROGEN IN DUNG-MAKING 233 



so result in a large evaporation of ammonia. With an 

 entirely covered yard it is often necessary to pump the 

 liquid over the litter again in order to maintain it in 

 a proper condition. Various materials have been sug- 

 gested to reduce the loss of ammonia. Gypsum, super- 

 phosphate, kainit, and other substances are sometimes 

 strewn about the cattle stalls and over the litter with the 

 idea of absorbing the ammonia whenever it is set free. 

 All these substances, however, possess but little practical 

 value; either they are too expensive, or they set up 

 some secondary injurious action which renders them 

 unsuitable. The only practical method is to keep the 

 manure tight and move it as little as possible during 

 either the making or the storage. It has been shown 

 that the loss on storage can be reduced by making a 

 foundation to the new dung-heap of a few inches of old 

 and well-rotted manure. 



It will thus be seen that the changes during the 

 making of farmyard manure are of a very complex 

 character. In the first place, we have the purely carbon 

 compounds of the litter turning into humus — this change 

 being accompanied by a loss of nearly half of the dry 

 matter. Secondly, the nitrogenous compounds are 

 being broken down in one or several stages into the 

 form of ammonia, some of which escapes. Lastly, other 

 bacterial changes under certain conditions of free 

 aeration causes part of the nitrogen to be lost by con- 

 version into gas, while at all times a certain amount of 

 reverse change from the soluble to the insoluble protein 

 state is taking place through the multiplication of the 

 bacteria themselves. No preservatives are of any avail, 

 but the loss of nitrogen can be best reduced by moving 

 the manure as little as possible and getting it on to the 

 land at the earliest available time. With these general 

 principles in mind we may now consider a little the 



