376 
Proceedings of the Eoyal Society of Edinburgh. [Sess. 
Results calculated on the Assumption that the Silicate is Kaolinite. 
i. 
II. 
Si0 2 .... 
44-3 
43-8 
A1 2 0 3 .... 
377 
37-2 
H 2 0 . . . . 
13-3 
13-2 
Excess H 2 0 . . 
1-5 
•65 
Free Si0 2 . . 
2*4 
2-8 
99-2 
97*7 
I. Present analysis. 
II. Analysis by Dr Fawsitt.* 
It is important to notice that the percentage of water is greater than 
that required to satisfy the formula for kaolinite. The excess of water is 
not sufficiently large, however, to prove that the mineral in question is 
halloysite, although it must be remembered that in the published analyses 
of halloysite this loosely combined water varies within wide limits. 
Effect of Boiling the Clay Substance with Concentrated 
Hydrochloric Acid. 
A portion of the washed clay (2*5 gms.) was boiled with concentrated 
hydrochloric acid (160 c.c.) for two hours. The residue was filtered off 
and the filtrate evaporated to dryness. The A1 2 0 3 was estimated after the 
small amount of Fe 2 0 3 had been removed. The result showed that 6 ’5 per 
cent, of A1 2 0 3 had been obtained from the clay by this treatment with the 
acid. The residue was again boiled with acid for four hours, the quantity 
of acid being also doubled. The percentage of A1 2 0 3 obtained by this 
digestion amounted to 16‘9, but the small amount of Fe 2 0 3 was also weighed 
along with the A1 2 0 3 , the amount of Fe 2 O s being so slight as not to affect 
the argument. The residue from the second estimation was boiled for seven 
hours, and 13’2 per cent, of A1 2 0 3 obtained. Altogether, therefore, 36*6 per 
cent, of A1 2 0 3 was got from the sample in this way. Since the analysis 
showed that the total A1 2 0 3 present amounted to 37*65 per cent., it is 
obvious that practically all the silicate of alumina is decomposed by boiling 
hydrochloric acid. 
That the A1 2 0 3 exists as a silicate is proved by the microscopic examina- 
tion. If the alumina is free, then the silica must be free ; and, as stated 
before, only a very small amount of free silica was found in the sample. 
* Proof in causa The Caledonian Railway Company against The Glenboig Union Fire- 
clay Company, Ltd., p. 168. 
