2 Oe ———— 
Juuy 26, 1918] 
this composition. When a complete chemical 
analysis of a glass sand is made, minute 
amounts of alumina, ferric and ferrous oxides, 
magnesia, lime, titanium oxide, traces of the 
alkalies, and varying amounts of water are 
usually found to be present. Some of these 
constituents are harmless, while others have a 
very deleterious effect upon the glass. 
Alumina imparts both desirable and unde- 
sirable properties to the resulting glass. It 
reduces the tendency of the glass to devitrify 
or crystallize. It decreases the solubility of 
the glass in water, weak acids, and other re- 
agents, which is very desirable in the case of 
bottles and chemical glassware. It increases 
the surface tension of the glass when chilled 
rapidly, which is beneficial in molding, as the 
glass will not take on the minor imperfections 
of the mold, while, on the other hand, it will 
still be sufficiently viscous to assume the gen- 
eral shape of the mold. It reduces the co- 
efficient of expansion of the glass and increases 
its tenacity, a feature also desirable in the case 
of bottles and chemical glassware. Alumina 
in glass facilitates annealing. It also makes 
the glass somewhat harder and a little more 
brilliant. An undesirable feature is that alu- 
mina tends to decrease the fusibility of the 
glass and increases its viscosity. It should, 
therefore, not be present in amounts exceeding 
3 per cent. Also glass cullet containing alu- 
mina does not mix well with other glass and, 
therefore, tends to produce cords or striz when 
used. The light blue tint noticeable in cer- 
tain glasses made from salt cake is thought 
by some observers to be due to alumina in the 
form of a compound analogous to ultramarine 
blue. Alumina may occur in glass sands in 
the form of kaolinite, mica, feldspar, or horn- 
blende. If it is present as kaolinite or mica 
it may be largely removed by washing. 
Tron in the form of either ferrie or ferrous 
oxides is the most detrimental impurity found 
in glass sands on account of its coloring effect 
upon the glass. Ferrous iron imparts a bluish 
green tint upon glass, while ferric iron pro- 
duces a yellow tint, which is not nearly so 
noticeable. Since most glass is made under 
reducing conditions, the green color is the 
SCIENCE 99 
one usually developed. Where the amount of 
iron present is small, this coloring effect can 
be in part overcome by the use of manganese 
dioxide, nickel oxide or selenium. For the 
best grades of optical glass the percentage of 
ferric oxide present in the sand should not 
exceed .002 per cent. For the better grades 
of lead flint used in the manufacture of cut 
glassware it should not exceed .02 per cent. 
In the ease of plate glass to be used for mirrors 
the ferric oxide should not be over .1 per cent., 
while in the case of plate glass to be used by 
transmitted light it may run up to .2 per 
cent. For window glass the amount may be 
as high as .5 per cent., while in the ease of 
ordinary green and brown bottles sands con- 
taining from .5 to as high as 7.0 per cent. 
ferric oxide is used. Iron may be present in 
the sand in the form of limonite, hematite, 
magnetite, ilmenite, biotite, hornblende, or 
chlorite. A little may also be introduced as 
metallic iron from the machinery used in 
crushing the sandstone to sand. [If it is pres- 
ent as limonite or hematite closely associated 
with the kaolinite or clay, it may be in large 
part removed by washing. If, on the other 
hand, the limonite or hematite adheres closely 
to the quartz grains washing will be of no 
avail. The other minerals mentioned can not 
be readily removed by washing. 
The small amounts of magnesia and lime 
occasionally present in glass sands have no 
detrimental effect upon the glass. All the 
common varieties such as plate, window, and 
bottle glass contain lime as an essential con- 
stituent. Magnesia is much more apt to be 
introduced into the glass batch through the 
limestone used than through the sand. The 
composition of this material, therefore, must 
be watched with respect to this constituent. 
Alkalies, likewise, enter into the composition 
of glass and the minute traces occasionally 
present in the sand, therefore, are not harmful. 
Titanium oxide never occurs in suflicient 
amounts to have any detrimental effects upon 
the glass. It usually occurs in the sand as 
minute hairlike inclusions of rutile in the 
quartz grains, themselves. In the case of the 
better grades of glass such as optical, lead 
