Scientific A griculture. 



184 



not effervesce upon the addition of either hot or cold vinegar, it probably contains 

 but little carbonate of lime and may be of doubtful value. This test, however, 

 should precede, and not be sustituted for, a carefnl chemical analysis. 



On account of the varying chemical composition of marl, it must be obvious 

 also that no definite rales as to the amounts which should be used in given cases can 

 be stated. On a soil where one has reason to think a ton of burnt lime should be 

 applied per acre, about 4 tons of a marl containing from 20 to 25 per cent of actua 

 lime (calcium oxid) should be employed. If the marl is twice as rich the amount 

 applied should be but 2 tons, etc. 



Marls vary somewhat in their physical characteristics, depending upon the 

 amounts and character of the earthy material associated with the carbonate of lime 

 If the marl is associated with clay it is exceptionally well adapted for use on sandy 

 soils, since the clay and carbonate of lime both tend to make such soils more compact 

 and rententive of manures and moisture. A marl containing sand would, on the 

 other hand, be better suited to clayey soils. According to Heini'ich, sand marl 

 may be applied to the soil immediately, but clay marls sometimes contain injurious 

 compounds of iron and sulphur, in which case it is not safe to use them until they 

 have been composted for two or three years, or long enough to effect the decomposi- 

 tion of the iron compound. 



Some so-called marls contain considerable quantities of phosphoric acid aud 

 potash in such foi'ms as to greatly enhance their fertilizing value. 



Phosphate of Limb is found as bone, guano, apatite, and in the form of 

 the well-known South Carolina, Florida, and Tennessee phosphate rock. The 

 better classes of phosphate rock contain but small quantities of carbonate of lime, 

 while others contain large amounts. The latter are unfitted on this account for 

 superphosphate manufacture. Both classes of phosphate when ground finely have 

 been found to be more or less effective upon acid soils, particular attention having 

 been devoted to their employment on acid muck or peat soils. These phosphates not 

 only seem to materially reduce the acid character of such soils, but after having 

 been in contact with them for some time the assimilability of the phosphoric acid 

 seems to materially increase. The lower-grade phosphates containing considerable 

 quantities of carbonate of lime are particularly effective upon acid soils. 



In employing undissolved phosphate rock upon acid soils, certain authorities 

 recommend following the application of the phosphate at an interval of some 

 months, or, if possible, a year, with a dressing of lime. This seems to be a reason- 

 able recommendation provided the plants to be grown are not injured by soil acidity. 



Superphosphates, which are prepared by treating phosphate rock, bone, 

 and boneblack with sulphuric acid, generally have about one-third of their lime 

 combined with phosphoric acid and two-thirds with sulphuric acid. The lime 

 combined with sulphuric acid is nothing more nor less than gypsum (land plaster). 

 For this and other reasons superphosphates may not work as well on acid muck 

 or peat soils as ordinary undissolved phosphate rock or ground bone, and if, as is 

 sometimes the case, a slight excess of sulphuric acid is present they may even have 

 a temporary injurious action upon upland soils which are deficient in carbonate 

 of lime. 



Basic Slag (Thomas Slag or Slag Meal) is a waste product obtained in 

 the manufacture of steel. It contains relatively more lime than the ordinary 

 high-grade phosphates, and the phosphoric acid in most cases (a few works have 

 put an inferior product on the European market) is possessed of a high degree of 

 assimilability. This product is as yet too little known in this country, and if sold 

 here as cheaply as it might be it would doubtless prove of great value to our 



