On the Causes of the Efficacy of Burnt Clay. 



503 



3. The above analyses distinctly prove the important fact, to 

 which I would invite particular attention, that the alkalies., more 

 particularly are rendered soluble to a considerable extent 

 in the process of burning-. 



• The temperature to which the clay has been exposed here 

 regulates the proportion of potash, rendered soluble in dilute 

 hvdrochloric acid, in a remarkable manner. 



- In the natural clay, only 0-*269 per cent, of potash were 

 soluble; whereas, in clay burnt at a moderate heat, and under 

 circumstances resembling those under which clay is burnt in the 

 field, the quantity of soluble potash amounted to more than three 

 times the former quantity. In Clay, No. II., the higher tem- 

 perature to which it was exposed caused a diminution in the 

 proportion of soluble potash; and in No. III. nearly the same 

 quantity of potash as in No. IV. was obtained : — 



Proportions of 

 Soluble Potash. 



Clay, No. 1. (actual state) . . . .0-269 

 „ No. II. (slightly burnt) . . . . 0-941 

 „ No. III. (stronger burnt) . . . 0-512 

 „ No, IV. Cover burnt) . . . .0-544 



The actual quantities of soda rendered more soluble in burning 

 are triflino:. but still sufficient] v large to confirm the fact that 

 soda is rendered more soluble in burning. The higher tempera- 

 ture applied in burning iVos. III. and IV. likewise was attended 

 with a slight diminution of soluble soda: — 



Proportions of 

 Soluble Soda. 



Clay, No. 1 0-220 



„ No. II 0-336 



„ No. Ill 0-314 



„ No. lY. ... . . . . 0-104 



4, A reference to the tabulated analytical results further 

 shows that the relative quantities of lime in the soluble portion 

 of each vary considerably : — 



Proportion of 

 Soluble Lime, calculated 

 as Carbonate. 



Clay, No. I. 0*740 



No. II 0-420 



„ No. Ill 0-550 



„ No. IV 0-188 



The three latter quantities are marked down in the analyses as 

 carbonate of lime, for the sake of comparison with No. I., in 

 which the lime really existed as carbonate of lime ; but as not 

 the slightest effervescence took place on dissolving the burnt 



