11 



Basic Phosphatic Slag. — This material is purchased chiefly 

 as a source of phosphoric acid, of which it contains 16 to 18 per 

 cent, mostly in an available form, in addition to 40 to 50 per cent 

 of lime. The exact form in which the lime is united with the 

 phosphoric acid is unknown, but recent investigations indicate a 

 silico phosphate of lime and ferrous oxide. ^ (CaO)5 FeO PsQs 

 Si02. The slag gives a decidedly alkaline reaction and a portion 

 of the combined lime is easily liberated and will probably act 

 in the soil as a base, but because of the complexity of the lime 

 combination it is quite impossible to state the exact percentage 

 of basic lime. Different samples also show from 2 to 7 1-2 per 

 cent of free lime (calcium oxide and calcium carbonate) but largely 

 as oxide. 



It would probably not be advisable to depend upon slag meal 

 for the purpose of producing that sharp change in mechanical 

 condition which is needed in the heavy, sour clays ; but by a rather 

 free use of slag meal many of the ordinarily looked for bene- 

 ficial effects of liming may be expected to follow; and in any 

 case, if soil has once been brought into satisfactory condition by 

 one heavy application of lime, we may doubtless depend upon 

 the lime in slag meal freely used as a source of phosphoric acid, to 

 hold the soil in a satisfactory condition as regards that element. 



Waste lime from tanneries can often be had for the cost of 

 carting. It is a desirable form of lime, probably largely carbonate 

 and hydrate. It may contain a large excess of water and not be 

 as convenient to apply as some other forms. It may be conven- 

 iently distributed, however, by means of a manure spreader. 

 Many samples contain considerable nitrogen, coming from hair 

 and fleshings from the hide, which gives the material an additional 

 value. 



Waste lime from gas houses is not as desirable as that from 

 tanneries. It is apt to contain injurious sulfites and sulfides and 

 should be left exposed to the action of the air for some time before 

 applying it to the land. The lime may be present in this ma,terial 

 in several forms, such as sulfate, sulfide, sulfite, carbonate and 

 hydrate. In many instances when in close proximity to its source, 

 the farmer can use this material, provided it can be had at a slight 

 expense. • 



Gypsum, sulfate of lime or land plaster, found in large quan- 

 tities in Nova Scotia and in Onondaga County, New York, is a 

 combination of lime and sulfuric acid. The Nova Scotia gypsum 

 contains substantially 34 per cent of lime and 48 per cent of sul- 

 furic acid ; the Onondaga plaster 30 per cent of lime, 32 . 5 per 

 cent of sulfuric acid, 8 or more percent of carbonic acid, and rather 



1. Morrison in the Journal of Agricultural Science, Vol. Ill, Part 2, p. 169; also Hendrick 

 in the Journal of the Society of Chemical Industry, Vol. XXVIII, No. 14, pp. 775-778. 



