502 On the Causes of the Efficacy of Burnt Clay. 



Clay from Hiintstile, near Biidgewatsr. 



No. I. 



No. II. 



No. III. 



No. IV. 



Water, driven off at 212= F. . . 

 Organic matter and water of com-) 



Insoluble matter (in dilute hydro-i 



chloric acid) J 



Soluble matter, consisting of — 



Oxides of iron and alumina . 



Phosphoric acid 



Chlorine and sulphuric acid . 

 Blagnesia (not determined ) . 



5-539 

 3-621 



8-1-100 



1-450 

 3-070 

 •740 

 -269 



•380 



traces 



1 9-160 



80-260 



1-380 

 8-245 

 -420 

 •941 



•165 



traces 



9-200 



81-845 



1-580 

 6-092 

 •550 

 •512 

 •314 

 -128 

 traces 



9-300 

 85-309 



1- 150 



2- 970 

 -188 

 -544 

 -104 



undetermined 

 traces 





99-389 



100-907 



100-221 



99-565 



On combustion with soda-lime, am- 

 monia (N H4, 0) produced in 



0*240 



0-019 

 0-017 

 0-018 





0-008 



These analytical results give rise to the following suggestions : — 



1. That, after burning, this clay has become much more 

 soluble than clay in its natural state. 



2. They not only teach generally that clay becom es more 

 soluble in burning, but that the temperature to which it is ex- 

 posed mainly regulates the solubility of the clay. A proper 

 temperature for burning clay is indeed a condition in the process 

 on which the success of the operation chiefly depends. Vv'e see, 

 from the preceding tabulated results, that clay, in 100 parts in 

 its natural state_, furnishes only 6 • 74 grains of soluble inorganic 

 matter, leaving 84 • 100 insoluble behind ; whilst the same clay, 

 burnt at a temperature and under circumstances under which the 

 organic matter was not altogether destroyed, left 80*260 of 

 insoluble matters. An increase of the temperature, sufficiently 

 high to burn off the small amount of organic matter which enters 

 into the composition of this clay, had the effect of reducing the 

 solubility of its constituents to about 1 J per cent.; and a more 

 protracted exposure to a still higher temperature had the effect 

 of a further reduction of its solubility to such an extent that this 

 over-burnt clay became- less soluble than the same clay in its 

 natural state : — 



Proportions of Proportions of 

 ' Soluble Inorganic Insoluble Inorganic 



Matters. Matters. 



Clay, No. I. (unburnt) . . . 6-740 84-100 

 „ . No. II. (slightly burnt) . . 10-580 80-260 

 „ No. III. (burnt stronger than II.) . 8-955 81-845 

 „ No. IV. (over burnt) . . . 5-391 85-309 



