709 



Minei.il 

 Superpliospak's. hom-x. 



Sulphate of lime and 



alkaline salts ... 41)'" 1 itS-S^ 



Insoluble ... ... 4 - oS 1-41 



lOO'OO 10000 



1 Containing nitrdgen ... ... 3-09 



Kqual to ammonia ... ... 375 



It will be as well to delay making a comparison between 

 superphosphates as a fertiliser and other phosphatic manures, until 

 we get t > the basic slag or Thomas's fertiliser, which I intend to 

 take next. 



THOMAS s PHOSPIIATKS, OK BASIC SLAC. 



In the year 1879 Thomas and Gilchrist patented their process 

 for the dephosphorising of iron in the making of steel. Before 

 that time the process in use was that known as the Bessemer, 

 which fai'ecl so far as to be ineffectual in reducing the amount of 

 phosphorous in the pig iron made from iron ore, which contained 

 too large a percentage of phosphorous to make steel. The 

 Bessemer process, known a; the acid process, had a lire-brick 

 lining in the converter. The Thomas- Gilchris: process is 

 the reverse, or basic process. The converter is lined with 

 a dolomite limestone ; the molten pig-iron is poured into the 

 converter, a quantity of lime equal to about 20 per cent, of the iron 

 in the converter is added, a hot blast of air, under pressure, is 

 injected through the molten mass, oxidising the phosphorus, which 

 in turn combines with the lime in the slag to form phosphate of 

 lime. The basic slag was first made in England, but it was in 

 Germany that it was rirst used as manure. To bring the slag into 

 a tit state to be used as a fertiliser, the molten slag is treated with 

 super-heated steam or poured into hot water to break it up into small 

 fragments and make it more easy to grind into the hue powder which 

 is necessary before it can be profitably applied to the land. Many 

 patents have been taken out to make or improve the slag as manure. 

 These have all been abandoned, as they were founded on illcon- 

 ceived notions of how the slag would act on plant life. The great 

 desideratum with the basic slag as a manure is that it should be in a 

 very tine powder, and if not in this state it should not be bought. 

 It contains from 14 to 20 per cent, of phosphoric acid, equal to 

 30 to 42 per cent, of tricalcic phosphate. The phosphoric acid in 

 the slag is not in the tricalcic state as in all other animal and mineral 

 phosphates, but it is in the tetracalcic form. So far I have avoided, 

 as much as possible, the use of scientific terms, but in this case I must 

 resort to scientific formula to explain the difference between these 

 two kinds of phosphates in order to enable the reader the better to 

 understand how the phosphates in the slag are more soluble than 

 those in natural phosphates. 



