STATISTICS ON MINERAL PRODUCTION 31

 SAND AND GRAVEL

 The sand produced in Florida is used principally for building, paving and road-making, filtering, molding, cutting, grinding and blast purposes. The gravel produced is reported as used for roofing material and for railroad ballast. 'Deposits of clayey sands and gravels occurring in the southern part of Jackson County have also been quarried and used as road surfacing materials. The total production of sand and gravel for 1918, as shown by returns from the producers, was 158,489 tons, valued at $48,768.
 The companies reporting the production of sand and gravel in Florida during 1918 are the following:
 Atlantic Coast Line Railroad Company.
 Akerman & Ellis, Lake Weir.
 Interlachen Gravel Company, Interlachen.
 Tallahassee Pressed Brick Company, Havana.
 Tampa Sand and Shell Company, Tampa.

 SAND-LIME BRICK

 The materials used in the. manufacture of sand-lime brick are sand and lime. The bonding power of the brick is due to the chemical reaction between these ingredients. The chemical changes occur in the presence of heat, pressure. and moisture and result in the formation of hydro-silicates of calcium and magnesium.
 The sand used in the manufacture of sand-lime should be comparatively pure and preferably with some variation in the size of the grains. The mixture of lime, sand and water is cut in the form of bricks and conveyed to a hardening cylinder. Necessary heat and pressure are obtained in the hardening cylinder adapted for the purpose. The sand-lime bricks are placed in this cylinder and subjected to a *pressure and temperature which vary according to the method of treatment.
 Two companies were actively efigaged in the manufacture of sand-lime brick in Florida during 1918 as follows:
 The Bond Sandstone Brick Company, Lake Helen.
 The Plant City Composite Brick Company, Plant City.
 The production of sand-lime brick in Florida during 1918, although not separately listed, is included in making up the total mineral production of the State.