Man's physical universe

xanabras

:

652 CREATIVE CHEMISTRY

Portland cement is high in Hme, whereas in glass silica predominates.

Ceramic products, such as pottery, earthenware, and porcelain, occupy,

generally, a position between these two extremes. The ceramic products

are of three types

(1) Unglazed, porous materials such as bricks, pottery, and terra

cotta.

(2) Partially glazed, porous materials such as earthenware and sanitary

ware.

(3) Nonporous materials such as stoneware, chinaware, and porcelain.

The type of product produced depends to a large extent on the very

careful selection and analysis of raw materials, although the great

improvements made in these products in

recent years have been paid for only by

Fig. 285. Left, old juice

bottle. Right, new juice

bottle, equal in capacity but

lighter in weight. Changes

in the design of glass bottles

to stronger bottles containing

less glass accounted for

an increased production capacity

of 2,500,000 gross

of glass containers in 1939.

(Courtesy of Industrial and

Engineering Chemistry,

News Edition, published

by the American Chemical

^*^^^^"^

very extensive research.

Glass Is One of the Most Important Industrial

Products of Today.

Ordinary "soft glass" such as used in

window panes and bottles is "lime-soda"

glass; that is, it is a sodium calcium silicate,

produced by melting together calcium

carbonate, sodium carbonate, and quartz

(sand, or Si02).

When these materials are

heated, carbon dioxide is evolved, and the

resulting products consist of about 1 part

sodium oxide, Na20, 1 part calcium oxide,

CaO, and 6 to 8 parts silica, Si02. The

Na20 and CaO may be partially or entirely

replaced by other oxides such as BaO, K2O,

ZnO, or PbO. Thus lead glass used in cutglass

ware contains PbO. The Si02 may

also be replaced by B2O3, P2O5, and other

oxides.

Heat-resisting glasses, for example,

are often borosilicate glasses, which are high

in boron oxide, B2O3, content.

Highly stable borosilicate glasses were

first developed in America some thirty years

ago.

Their resistance to mechanical shock

and sudden temperature changes has brought them into wide use for

cooking utensils, while their resistance to chemical reagents, along with