In the first place, it must be distinctly understood that the form in which ammonia escapes from the manure-heap is not, as is so commonly erroneously stated in agricultural text-books, as "free" ammonia. Whenever ammonia is brought into contact with carbonic acid, carbonate of ammonia is formed. When it is remembered that carbonic acid is by far the most abundant of the gaseous products of the decomposition of organic matter, it will be at once seen that free ammonia could not exist under such circumstances. 1. In the case of _hydrochloric acid_, the following chemical equation will represent the nature of the reaction-- 2HCl + (NH_{4})_{2}CO_{3} = 2NH_{4}Cl + H_{2}O+CO_{2} (Hydrochloric (carbonate of ammonia,) (sal-ammoniac,) (carbonic acid.) acid,) 2. In the case of _sulphuric acid_, the equation will be-- H_{2}SO_{4} + (NH_{4})_{2}CO_{3} = (NH_{4})_{2}SO_{4} + H_{2}O+CO_{2} (Sulphuric (carbonate of (sulphate of ammonia,) (carbonic acid.) acid,) ammonia,) 3. With _gypsum_ (CaSO_{4})-- CaSO_{4} + (NH_{4})_{2}CO_{3} = CaCO_{3} + (NH_{4})_{2}SO_{4} (Gypsum,) (carbonate of (calcium (sulphate of ammonia.) ammonia,) carbonate,) 4. With _copperas_ (FeSO_{4})-- FeSO_{4} + (NH_{4})_{2}CO_{3} = FeCO_{3} + (NH_{4})_{2}SO_{4} (Sulphate of (carbonate of (ferrous (sulphate of ammonia.) iron,) ammonia,) carbonate,) 5. With _sulphate of magnesia_ (MgSO_{4})-- MgSO_{4} + (NH_{4})_{2}CO_{3} = MgCO_{3} + (NH_{4})_{2}SO_{4} (Sulphate of (carbonate of (carbonate of (sulphate of magnesia,) ammonia,) magnesia,) ammonia.) Reference has been made to the fact that magnesium sulphate may probably not only fix the ammonia, but the phosphoric acid. When magnesium sulphate, soluble phosphoric acid, and ammonia are brought in contact with one another, the double insoluble phosphate of ammonium and magnesium (MgNH_{4}PO_{4}6Aq) is formed. While such a reaction is possible, it is highly improbable that it takes place to any extent. The double phosphate is a crystalline salt which only separates after a considerable time, and in the presence of a large excess of ammonia. NOTE XI. (p. 250). ANALYSES OF COW-MANURE.[181]