414 
Company, near Paris, manufactures for this purpose glass tiles 
4 to 6 mm. in thickness and 24 cent. by 24 cent. The side which 
is against the cement is striated, to better hold to the cement, whilst 
the other side is smooth. For the floor, larger and thicker tiles are 
used. These tiles are set in soft cement mortar, and care should 
be taken not to allow any air to remain between the cement and 
the tile, which should be soaked in water before using. 
Apart from these brick and cement vats, some are constructed 
of a combination of iron and cement, or ferro-concrete, and are 
estensively used in Algeria. They are known as sidero-cement vats, 
and consist of a framework of iron rods, either rectangular or cylin- 
drical, as desired. On this iron lattice-work, which has the shape 
of the vat, cement mortar is plastered, and the desired polish is 
given, to the surface. 
These vats are thinner than the brick ones, whilst their cohesion 
is much greater, for although cement can stand a considerable 
crushing strain, it lacks in cohesion, or in other words, its tensile 
strain is not so great. 
In Algeria, where these sidero-cement vats are in great favour, 
the cost was set down some years ago as ranging between 2s. 6d. 
to 3s. 4d. per hectolitre (22 gallons) for small vats, and less for 
larger ones. These prices are equivalent to 114d. to 134d. per gal- 
lon, wooden vats costing 8 frances per hectolitre or 334d. per gallon. 
The combination of the iron and the cement, instead of being 
an element of weakness, considerably adds to the strength and 
durability of the vats. Both these substances expand or contract 
at the same rate, and therefore no dislocation ensues, whilst, on the 
other hand, the elose-fitting cement covering effectually preserves 
the iron from rusting. 
When these cement vats are made, and dry, they are first filled 
with water, and although they may sweat a little at first, this soon 
stops. 
It is necessary before using these vats to also wash them with 
some solution which will dissolve and neutralise the traces of lime 
which may be left close to the surface, viz., a weak acid wash, such 
as a 10 per cent. solution of tartarie acid, or of sulphuric acid; a 
protective coating of tartrate of lime or of sulphate of lime is thus 
formed. 
Fluoride of magnesium, 20°—25° Baumé, is applied with a 
brush, two or three times, with an interval of 12 hours between each, 
until the cement has absorbed about 14ozs. per square yard. When 
dry apply a single coat of fluoride of aluminium at 15° B., using 
7ozs. per square yard. After drying wash with water until the 
salty taste of the fluoride has gone. The vat may then be used 
without risk. 
