516 MISCELLANEOUS FARM SUBJECTS 



should first have a sample of it analyzed. If the material will not 

 effervesce upon the addition of either hot or cold vinegar, it proba- 

 bly contains but little carbonate of lime and may be of doubtful 

 value. This test, however, should precede, and not be substituted 

 for, a careful chemical analysis. 



On account of the varying chemical composition of marl, it 

 must be obvious also that no definite rules 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 actual 

 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, depend- 

 ing 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 retentive of manures and moisture. A marl containing sand 

 would, on the other hand, be better suited to clayey soils. Accord- 

 ing to Heinrich, 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 

 decomposition of the iron compounds. Some so-called marls con- 

 tain considerable quantities of phosphoric acid and potash in such 

 forms as to greatly enhance their fertilizing value. 



Phosphate of lime 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 superphos- 

 phate manufacture. Both classes of phosphate when ground finely 

 have been found to be more or less effective upon acid soils, parti- 

 cular 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 con- 

 tact with them for some time the assimilability of the phosphoric 

 acid seems to materially increase. The lower-grade phosphates con- 

 taining considerable quantities of carbonate of lime are particularly 

 effective upon acid soils. 



In employing undissolved phosphate rock upon acid soils, cer- 

 tain authorities recommend following the application of the phos- 

 phate at an interval of some months, or, if possible, a year, with a 

 dressing of lime. This seems to be a reasonable 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 



