Lerrvs & Bhake—The Carbonic Anhydride of the Atmosphere. 153 
B. 10:0 c.c. of the solution after contact with silica and filtra- 
tion were treated in the same way until the same shade 
of pink remained. 
A now required 2 drops more acid for decolorization. Total 
acid used 26°6 c.c. 
B required 16 drops. Total acid used 7°4 e.c. 
The remainder of the weak baryta solution and silica were 
rotated in the paraffined bottle for an additional period of three 
days. 
A. 10:0 cc. of the original baryta treated as before required 
an addition of 2 drops of acid for final decolorization. 
B. 10:0 cc. of the silicated solution required 22 drops. 
Total acid used 6.75 c.c. 
After rotating for three more days— 
A still required 2 drops for decolorization. 
B required 26 drops. Total acid used 6°55 c.c. 
(3.) 0°212 grm. anhydrous carbonate of soda and 0:12 grm. 
anhydrous silica, quantities equivalent to Na,CO; + SiO, were 
fused in a platinum crucible until all action was over. The 
resulting metasilicate of soda was then dissolved and titrated 
with decinormal acid, with phenol-phthalein as indicator. The 
colour faded so slowly that the exact point of decolorization was 
very hard to determine. At first it was judged that 387 c.c. of 
acid had effected it, but after a time a faint pink shade seemed 
to have returned. Finally 37:9 ¢c.c. of the standard acid were 
added. 0212 grm. of carbonate of soda would, if converted 
into caustic soda, require 40 c.c. of the acid. 
Thus metasilicate of soda, when titrated with phenol-phtha- 
lein as indicator behaves almost like caustic soda. 
1 It is, perhaps, superfluous to state, when phenol-phthalein is used neutralization 
is indicated when the reaction 
NazCO3 + HCl = NaHCOs + NaCl 
has occurred. 
The quantity of carbonate of soda employed in the above experiment requires 
20 c.c of decinormal acid for this reaction. Metasilicate of soda is, therefore, nearly 
twice as strong in alkaline effect as the carbonate. 
