162 J. M. Ordway on Waterglass. 
are required on the part of the workman that he may stop at 
just the right point. An excess of sulphate can be remedied, 
but an excess of coal is hard to get rid of. When the melted 
mass has become smooth and homogeneous and light colored, it 
may be decolorized with arseniate of soda and drawn out, the 
hoes being changed as they get hot and pliant. 
For making a liquid or pasty silicate, the glass coarsely ground 
may be boiled with water till the solution stands at about 25° B. 
after cooling. If it is made much stronger it will not settle 
readily. Some dissolve waterglass by blowing steam directly 
into the water, but in that case the solution goes on very slowly, 
becatise the heat is insufficient. It is far better to have an iron 
kettle heated by a fire. After being allowed to deposit the in- 
soluble matter, the liquid may be concentrated by evaporation to 
any required degree within certain limits. When it becomes 
difficulty; for the silicate then rapidly adheres to the kettle 
and there is needed very diligent scraping with a chisel-pointed 
bar to keep the bottom and sides of the vessel clear of the 
Spongy coating. And to push the evaporation to dryness, 18 
quite out of the question. Sesquisilicate of soda cannot conven- 
B. 
When we wish to obtain the greatest possible relative amount 
of silica in solution, it is necessary to make the glass of none 
pure quartz and pure Base an insoluble glass cannot be pre- 
d. “For if we ta } 
