152 Scientific Proceedings, Royal Dublin Society. 
Before discussing the cause of increase in the alkalinity of the 
baryta solution, we pass to the consideration of another effect 
produced by the action of baryta water on glass, whereby the 
delicacy of the phenol-phthalein colour reaction is not only inter- 
fered with but practically destroyed for all accurate determi- 
nations. 
Effect of the presence of alkaline or soluble silicates on the delicacy 
of the phenol-phthalein colour reaction during titration with an 
acid.—We noticed repeatedly in the preceding experiments that 
the final decolorization of the phenol-phthalein by acid occurred 
quite differently in the baryta water before and after the latter 
had been in contact with glass. 
In the former case a single drop or at most two drops of acid 
were sufficient to discharge the faint pink shade of colour which 
experience had taught us indicated the near approach of neutrality. 
Whereas, in the latter case a much larger quantity of acid was 
necessary, and the colour faded away almost imperceptibly as it 
was added, rendering the observation of final decolorization very 
difficult and uncertain. 
It occurred to us that this effect was very possibly due to the 
presence of dissolved silicates; and to decide the question the 
following experiments were made :— 
(1.) A. A weak solution of caustic potash was titrated, after 
the addition of a drop of phenol-phthalein solution, with dilute 
hydrochloric acid until a certain faint pink colour remained. 
B. A weak solution of silicate of soda was mixed with the 
same quantity of phenol-phthalein and titrated with 
the same acid, and in a vessel of the same size, until the 
same tint was obtained. 
A then required 5 drops of acid for complete decolorization. 
B required 40 drops, and even then a trace of pink remained. 
(2.) Pure unignited silica was rotated by a turbine in a 
paraffiined bottle with baryta water for five days. 
A. 10:0 c.c. of the original baryta water were mixed with a 
drop of phenol-phthalein solution, and the standard 
hydrochloric acid added until a faint pink colour re- 
sulted. 
