208 CHEMICAL MANUEES. 



acid has been the subject of profound researches by E. Jensch 

 which are of so much the greater interest because the sokibihty in 

 the same solvents of the calcareous silicates always present in basic 

 slag were determined at the same time. Jensch's researches were 

 made on basic slags of very different ages and origins for comparison. 

 He determined the solubility of both Podolia phosphorites and 

 Somme phosphate. The method pursued consisted in mixing each 

 time 1 grm. of the substance with 150 c.c. of the solvent concentra- 

 tion 1 in 20, exposing the mixture during twelve hours to a tempera- 

 ture of 50 to 70° C, then to dilute the solution in 100 c.c. of water. 

 The liquid was heated to boiling, filtered to separate the insoluble, 

 ignited, and the phosphoric acid titrated in the usual way. The 

 difference in the contents of the different elements in the residue on 

 the one hand and the raw material on the other hand, gives the 

 quantities dissolved by the organic acid. Jensch operated on eleven 

 samples of basic slag reduced to a fine powder (1 to 11) ; three 

 samples of crystals of raw slag (12, 13, 14). A sample of Podolian 

 phosphorite (15) and a sample of Somme phosphate (16). The follow- 

 ing table (p. 210) gives on the one hand the content of the substances 

 examined in silica, lime and phosphoric acid, on the other hand, the 

 quantities of phosphoric acid dissolved by the different solvents, also 

 the centesimal amounts remaining undissolved in the residues. 

 These figures show that the phosphoric acid behaves perceptibly in 

 the same manner in basic slags containing more than 18 per cent of 

 that acid as in those which only contain it in small proportion. 

 Thus it is that rich basic slags in current use in agriculture only 

 contain O'lS to 0*20 insoluble in citric acid, whilst low strength 

 basic slags only contain 0-04 to 0-14 per cent. The solubility in 

 oxalic acid yields equally concordant results. That acid dissolves 

 tetracalcic phosphate and only gives a slight residue of insoluble 

 which consists probably of tricalcic phosphate. The crystals sepa- 

 rated from the iDasic slags (12, 13, 14) show a still greater solubility. 

 The other organic acids used in this series of experiments act less 

 energetically on the phosphates of basic slag ; however, here again a 

 certain uniformity can be established between the solubility of the 

 different phosphates. 



The silicates, which are highly basic, although of a composition 

 often very variable for the same origin, are distinguished by their 

 solubility in the organic acids, a property which is absolutely awanting 

 in the silicate compounds of the natural phosphates, phosphorite, 

 apatite, etc. It follows that the degree of solubility of the phos- 

 phoric acid of basic slag depends on the nature of the calcareous 

 silicates contained therein. Again, if the fragments of basic slags 

 show a uniform crystalline structure, that is to say if they are de- 

 prived of agglomerations of caustic lime, which are sometimes ob- 

 served therein, their content in free lime will be very small and will 



