202 



CHEMICAL MANUEES. 



inclined on its axes, and the current of air is suspended and the 

 hquid slag floating on the cast-iron is poured into a metallic truck 

 forming a case and containing a certain quantity of finely pulverized 

 fused silica. The weight of the slag in one of these trucks may 

 reach 4| tons and even more. The whole is conveyed on rails to 

 the spot where it is to be handled, and after cooling, facilitated by 

 sprinkHng with water, the mass is removed from the truck and 

 discharged into a crushing shed. 



The Nature of Basic Slag.- — Basic slag occurs as more or less 

 bulky blackish fragments, porous, strewn with tablets of steel and 

 of great densitv. It slakes in the air ; the caustic lime absorbs 

 moisture and carbonic acid and the ferrous oxide oxidizes. Con- 

 trary to an opinion expressed at first, the absorption of carbonic 

 acid decomposes the tetrabasic phosphate. In the porous part of 

 the slag translucid crystals are met with, rhombic tablettes, hexagonal 

 prisms, and monoclinic needles 10 to 15 mm. long, of a grey, browTi 

 or blue (produced by FeOj colour intermingled or ranged symmetri- 

 cally. These crystals consist principally of tetrabasic phosphate of 

 lime, Ca^P.^Og. They have been the object of very interesting re- 

 searches, the principal points of which will now be summarized. 



Tetrajjhosphate of Calcium. — Ca^P.p., may be regarded as being- 

 the neutral salt of an octobasic diphosphoric acid P20(0Hjg not yet 

 produced in the free state, the structural formula of which would 

 be the following : — 







OH 



OH 



OH 



OH 



OH 



OH- 



OH 



OH 



and that of the corresponding 

 tetra calcic phosphate 



O 



P - 



o>c- 



g>Ca 

 0>Ca 



The presence of this compound in basic slag has been determined 

 by a great number of scientists, so that there can be no doubt as to 

 the soundness of the hypothesis enunciated above. The small blue 

 crystals which are found in the paste, and more especially in the 

 geodes of the slag, were studied from a crystallographic point of 

 view by A. Eichard, who refers them to the orthorhombic system, 

 and notes amongst their properties a strong double refraction and 

 a very marked dichroism, the same crystal appearing colourless or 

 a beautiful cobalt blue in two rectangular positions. Prof. Carnot 

 at this time termed these crystals silico phosphates of lime and gave 

 them the formula PP-SiO.^SCaO. In the same year Hilgenstock 

 examined the other crystals. He found in the scoriae of these, crystals 

 in the form of thin rectangular tablets coloui less or of a light brown 

 according to the thickness. He placed them in the rhombic system. 



