23

Carbon. Dioxide.” *
Carbon dioxide is liberated from magnesite at a temperature about
370 degrees Centrigrade? lower than from limestone or calcite. Magnesite
has, therefore, been used for producing carbon dioxide, but other and
cheaper methods of manufacture have led to a decreased production from
this source.

Sorel Cement.*

If magnesite be burned to a red heat a product known as “caustic,
calcined magnesite” is formed, which is a mixture of magnesia and
magnesite with a carbon dioxide content of less than 8 per cent of COs.
This product, if free from certain impurities, sets into a hard cement when
mixed with a solution of magnesium chloride of a certain strength. This
mixture, together with fillers, such as sawdust, ground cork, ashes, china
clay, asbestos, serpentine, tale, and colouring material, ochre, etc., is used
in the manufacture of flooring, artificial marble, and tiles. When success-
fully laid, the floors are said to be smooth, resilient, and not liable to crack.
They are readily coloured, take a good polish, prevent the escape of heat,
- and are resistamt to fire. Failures in the use of this cement have been
ascribed to lack of uniformity in the raw materials used, improper mixing,
deterioration of the materials before construction, improper foundations,
and lack of experience in the laying of the floors. Sorel cement is one of
the products which eventually may be successfully produced from high
grade hydromagnesites.

Refractory Materials.

When magnesite is raised to a white heat (1,700 degrees C.) and
practically all the carbon dioxide is driven off, the resulting magnesia
(MgO) is chemically inert and very refractory.’ The product is known as
“‘dead-burned magnesite”’ and is used either as magnesite brick or, crushed
to pea size, for the lining of basic steel furnaces, copper convertors, furnaces
for refining lead, electrical and other furnaces. The crushed material is
employed as a lining for the bottom of open-hearth furnaces, rotary kilns
in Portland cement manufacture, and in making crucibles and cupels.
The foregoing comprise the principal uses of crystalline magnesite.

Digestion of Wood Pulp.

Magnesium bisulphite made from calcined magnesia, when boiled
with pulp wood, dissolves the non-cellulose matter in the wood and the
resulting pulp is used in the making of paper.

Manufacture of Magnesium Salts.

“Tight magnesium carbonate” or magnesia alba levis (MgOH
3MgCoO;) is manufactured in some instances from magnesite. It is used
as a heat insulator on pipes, etc., as a fire retarding paint, as a toilet pre-

1U.S. Geol. Surv., Mineral resources of the U.S. for 1913, pt. IT, p. 446.
2Geol. Surv., Can., Mem. 98, p. 6.
3Chemical abstracts for 1917, p. 562.
4U.S. Geol. Sury., Mineral resources of the U.S., 1913, pt. IT, pp. 447, 450-453.
, care melting point of MgO is 2,800°C., CaO, 2,572° C., AleOs, 2,050°C., Cr2O3, 1,990°C. Jour. Franklin Inst., 1913,
p. 587.