[235] _Vide_ Professor Wagner's pamphlet, 'Der Duengewerth und die rationelle Verwendung der Thomas Schlacke,' Darmstadt, 1888. [236] No. 1 fineness was such as passed entirely through a fine gauze sieve of 250 wires to the linear inch. [237] No. 2 fineness was such as passed entirely through the regular standard sieve--_i.e._, containing 120 wires to the linear inch. [238] No. 3 was what would not pass through the standard sieve. [239] 'Transactions of the Highland and Agricultural Society,' 1891; 'Chemical News,' 1893. APPENDIX TO CHAPTER XIV. NOTE (p. 404). For those more particularly interested, we append a full analysis of the slag, taken from Messrs Stead and Ribsdale's paper in the 'Journal of the Iron and Steel Institute,' 1887, vol. i. p. 222:-- Lime 41.58 Magnesia 6.14 Alumina 2.57 Peroxide of iron 8.54 Protoxide of iron 13.62 Protoxide of manganese 3.79 Protoxide of vanadium 1.29 Silica 7.38 Sulphur } .23 Calcium } .31 Sulphuric anhydride .12 Phosphoric acid 14.36 ----- 99.93 CHAPTER XV. POTASSIC MANURES. _Relative Importance._ In Chapter VI. we pointed out that of the three manurial ingredients potash was the one most abundantly occurring, and that, consequently, the necessity of adding it in the form of an artificial manure existed less frequently than in the case of nitrogen or phosphoric acid. It was further pointed out that, under the ordinary conditions of agriculture, a greater restoration to the soil of the potash removed in the crops was made in the straw used in farmyard manure than was the case with regard to the other two ingredients. Despite these facts, there are many cases where the addition of potassic manures is of the highest importance in increasing plant-growth. It will be well, therefore, to devote a little space to considering our different potassic manures and their respective action. _Scottish Soils supplied with Potash._ Potassic manures are not so valuable in this country since experience has shown that most Scottish soils are abundantly supplied with this manurial ingredient. Moreover, under the conditions of most European farming, there seems to be a steady gain to the soil of potash. In America, however, the action of potash as a manure seems to be more strikingly illustrated. Indeed, wherever forage crops or straw are sold off the farm in large quantities, or where beets, cabbages, carrots, potatoes, onions, &c., are also grown in large quantities, the necessity for potash manuring generally arises. _Sources of Potassic Manures._