164 J. M. Ordway on Waterglass. 
riskly and without intermission, during the whole time of heat- 
ing. If there is no uncombined sand in the article under treat- 
ment, the cessation of the gritty feeling, shows plainly when a 
farther application of heat is unnecessary. For a well fluxed 
sesquisilicate of soda, 15 minutes boiling is quite sufficient. Any 
uncombined sand present in a sample, causes an uncertainty in 
the time required. Should there. be a gritty residue after half 
an hour’s boiling, it is advisable to stop and make a preliminary 
testing. If we find less than 28 per cent of alkali indicated, it 
is best to start anew and heat at least an hour and a half. 
When the operation is finished, if sulphuric acid has been 
used, the tested liquid itself can be ad down, and then the 
silica is left in a coarse granular form, easy to wash, collect, ignite 
and weigh. If the precipitation of the silica is effected with au 
ammonia salt, the residue is likely to be very bulky, and so fine 
and light that it requires no little eare to keep it from blowing 
partly away during ignition. 
An excess of nitric or chlorhydric acid added to very dilute 
waterglass, causes no apparent change for a long time, and in 4 
weak solution so treated we may test for sulphates or cblorids, 
for iron or for arsenic acid, without previously removing the 
silica. For the quantitative determination of sulphate and chlorid 
it is best to treat the silicate solution with an excess of nitrate of 
ammonia instead of an acid, and thus prevent any loss of chlorine 
in drying down, 
If sulphids are present in a liquid waterglass, a small bit of 
sulphate or carbonate of lead dropped in will soon become ai 
olored. : 
When the per-centage of water is to be ascertained, it is not 
well to heat the solution by itself, for in such a case it finally 
expands to an enormously bulky, vesicular, unmanageable mass. 
ate 
m 
oe 
