156 Scientific Proceedings, Royal Dublin Society. 
50 ¢.c. contained 0:0085 grm. SiO, and -2811 grm. BaO, 
giving the ratio of about SiO, : 13 BaO. 
The residue left in the paraffined bottle was washed with distilled 
water until the washings no longer showed an alkaline reaction, : 
and it was then treated at ordinary temperatures for twenty-four 
hours with decinormal hydrochloric acid. The resulting solution 
was filtered, and a determination made of the silica and baryta 
which it contained. The silica amounted to 0°0102 grm., and the 
baryta (BaO) to 08370 grm., quantities which about correspond 
with the ratio SiO, : 20 BaO. 
Since writing this paper our attention has been called to the in- 
teresting work both of Kohlrausch' and of Kahlenberg and Lincoln? 
on solutions of alkaline silicates. 
The former by conductivity determinations, and the latter by 
both conductivity and cryoscopic measurements, have shown that 
when such solutions are sufficiently diluted, hydrolytic decomposi- 
tion of the dissolved salt occurs, yielding alkaline hydrate and 
colloidal silicic acid. 
This would explain the result obtained by us on titrating a 
solution of metasilicate of soda, but on the other hand it renders 
an explanation of the fact observed by us, that a very dilute solu- 
tion of barium hydrate dissolves amorphous silica with partial 
neutralization, extremely difficult. For Kahlenberg and Lincoln 
tell us that “silicates of the general formulae M,Si0;, and MHSi0s;, 
are practically hydrolytically dissociated when 1 gram molecule is 
contained in 48 litres. Silicates of the general formula M,Si,0i 
are practically decomposed by water when 1 gram molecule is 
present in 128 litres.” As our baryta water was weaker than centi- 
normal it is not easy to see how it should have any solvent action 
on silica if the above statement is true, and much less that it 
should become practically neutralized in the process. 
[Parr IT. 
1 Kohlrausch, ‘‘ Zeitschr. f. phys. Chem.,’’ 12 [1893], p. 773. 
2 Kahlenberg and Lincoln, ‘‘ Journ. Phys. Chemistry,”’ vol. i1., p. 77. 
