CHAPTER XI. 

 MANUFACTURE OF BASIC SLAG. 



A Betrospectice Glance. — In the early days of the application of the 

 Thorn IS and Gilchrist process, the hasic slag from the dephosphoriza- 

 tion formed a cumbersome ballast. Gradually the idea came to use 

 it as a manure, but agronomists did not, at first sight, come across 

 the true method of utilizing this waste. They imagined, by analogy 

 with mineral phosphates, that it would be necessary to cause it to 

 undergo a similar conversion as the latter. But looking to the 

 nature of the slag itself, one would not dream of converting it into 

 superphosphate. Precipitated phosphate of lime was therefore made 

 from it by Scheibler's patent, which was put on the market as 

 Thomas jjrecipitate either alone or mixed with nitrate or ammonia. 

 This precipitate, prepared by the Fertilitas Company, tested 32 to 35 

 per cent of phosphoric acid, of which 80 to 90 per cent was soluble 

 in citrate. In May, 1885, The Anglo-Continental Co. took up the 

 sale of the new product, but in spite of the support of this powerful 

 company, Thomas precipitate did not have great success, looking 

 more especially to its high price. At the same time, G. Hoyermann 

 and Heinrich Albert commenced researches to determine the fertiliz- 

 ing value of the basic slag in its natural state. Hoyermann engaged 

 a certain number of farmers of the province of Hanover to spread 

 finely ground basic slag on marshy lands and meadows. On his 

 part, Heinrich Albert, who had for a long time recognized the solvent 

 role of the acids elaborated by the roots of plants, devoted several 

 years to the study of the action exerted on phosphates by weak 

 solvents. He remarked that peat finely ground and kept very moist 

 constituted a somewhat energetic solvent for phosphate. He ap- 

 plied his methods to basic slag and obtained excellent results. In 

 1885 the agricultural station of Darmstadt entered the same field, 

 and in its turn made cultural experiments with basic slag, thanks 

 especially to the financial support of the syndicate of German manure 

 manufacturers. These experiments were continued for several years, 

 and in 1889 Dr. Paul Wagner published the results obtained. 

 Nevertheless, manure manufacturers themselves remained sceptical, 

 and only two of them consented to deal with the metallurgical firms 

 for the supplv of basic slag. Their hesitation will be readilv under- 



(197) 



