NITROGENOUS MANURES. 255 



Commercial Sulphate of Ammonia. — Commercial sulphate of 

 ammonia contains in round figures 20 per cent of nitrogen. 

 Generally 24-5 per cent of ammonia, the term used in Great 

 Britain, is guaranteed ; however, there is generally found salts up tO' 

 25 per cent of ammonia. ^ When pure, sulphate of ammonia is white, 

 but it generally contains traces of tar or its derivatives. The yellow 

 colour is often produced by the presence of arsenious sulphide, 

 the green coloration by cyanide of iron, but these colours dis- 

 appear on drying. It is known that ammonia is converted in the 

 soil by a ferment into nitric acid NH3 + 40 = HNO.3 + Hp, but 

 this nitrification is only possible if the sulphuric acid of this salt be 

 combined with lime. Commercial sulphate of ammonia should be 

 neutral and contain as a maximum 2 per cent of water ; when it 

 contains only 1 per cent of rhodanate of ammonia (NH^SCN), 

 ammonium sulpho-cyanide, it is injurious to plants, according to- 

 Maercker. But these impure products are no longer manufactured. 

 Sulphate of ammonia is dried in a steam dryer, crushed in ball 

 mills with a No. 50 sieve or in Carr's disintegrator. Bags which 

 have contained sulphate of ammonia, like nitre bags, are dried and 

 cleaned bv beating or bv washinc^ with water ; the wash water, if it 

 be not desired to evaporate it, is sent to the concentration pan. 



As already mentioned, the strength of sulphate of ammonia may 

 be expressed in two ways. In France it is customary to give the 

 percentage in nitrogen ; in other countries, especially in Great 

 Britain, it is given as ammonia, so that the same sulphate has a 

 strength 21'21 per cent or 25-75 per cent according to the designa- 

 tion adopted. To prevent any confusion, it suffices to multiply the 

 strength in ammonia by the nuinher 0'8235 to obtain the correspond- 

 ing p>ercentage of nitrogen. Inversely, by multiplying the pjercentage- 

 of nitrogen by 1-214 the corresponding piercentage of ammonia is 

 obtained. The following table gives the calculations for all strengths 

 met with in commerce : — 



1 Pure sulphate of ammonia contains 25-7 of ammonia XH3. But com- 

 mercial sulphate always contains free acid and other impurities including 

 moisture. Even good commercial sulphate of ammonia contains enough im- 

 purities to stultify the " complete " analysis as usually performed. All the nitrogen 

 is calculated to sulphate, although very evidently it is not all present as sul- 

 phate. There are traces of substances with lower equivalents than sulphuric 

 acid, so that when the nitrogen is calculated to ammonium sulphate, the free acid 

 determined and the combined acid also as well as the moisture, no manipulation 

 of the figures will bring them down to 100 per cent. A trace of this " rhodanate " 

 of ammonia, so rich in nitrogen, would explain all this, and the particulars given 

 in the following paragraph throw still further hght on the subject. The re- 

 inventor of a back titration process for testing sulphate of ammonia took no 

 account of free acid ! Needless to say, that when facts like the above were also 

 brought before him, he could not grasp their significance. An accurate and 

 complete analysis of even fairly pure commercial sulphate of ammonia is not so 

 simple a matter as at first sight appears. It shows great lack of skill and 

 judgment to combine the extraneous nitrogen in sulphate of ammonia with the 

 free acid, and thus report a larger percentage of sulphate of ammonia than is 

 actually present. 



