GENERAL DISCUSSION OF CLAYS. 



No OF FUSION FUSION 



CONE. COMPOSITION. POINT POINT 



CENT. FAHR. 

 0.3 K 2 O ^ 



21 L 4.4 A1 2 3 44 Si O 2 . 1550 2822 

 0.7 Ca O 



0.3 K 2 O ^) 



22 [ 4.9 Al a 3 49 Si O 2 1570 2858 

 0.7 Ca O J 



0.3 K 2 O 



23 [ 5.4 A1 2 O 3 54 Si O 2 1590 2894 

 0.7 Ca O 



0.3 K 2 O 



24 \. 6.0 Al a 3 60 Si 2 1610 2930 



0.7 Ca O 



I 6.6 AU 



0.3 K 2 O 



25 I- 6.6 Ala O 3 66 Si O 2 1630 ' 2966 



0.7 Ca O 



.3 K 2 O 



26 ]. 7.2 A1 2 O 8 72 Si O 2 1650 3002 

 .7 Ca O 



.3 K 2 O 



27 J. 20 A1 2 O 3 200 Si O 2 1670 3038 

 .7 Ca O 



28 AI 2 O 3 10 Si O 2 1690 3074 



29 A1 2 O 3 8 Si O 2 1710 3110 



30 Ala O 3 6 Si O 2 1730 3146 



31 Al a O 3 5 Si O 2 1750 3182 



32 A1 2 O 3 4 Si O 2 1770 3218 



33 Ala O 3 3 Si O 2 1790 3254 



34 A1 2 O 3 2.5 Si O 2 1810 3290 



35 Ala O 3 2 Si O 2 1830 3326 



36 Ala O 3 2 Si O 2 1850 3362 



The theory of these pyramids is that the cone bends 

 over as the temperature approaches its fusing point, 

 and when this is reached, the tip touches the base. If 

 the heat is raised too rapidly, those cones which con- 

 tain much iron swell and blister and do not bend over, 

 and the best results are obtained by the slow softening 

 of the cone under a gradually rising temperature. 



For practical purposes these cones are considered 

 sufficiently accurate. 



In actual use they are placed in the kiln at a point 



