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was found in one specimen taken from the core of a main pier. Various investi-
gators have observed that little absorption of atmospheric carbon dioxide takes
place until mortar is fairly dry, but not completely dry. The process of carbonation
is greatly accelerated by subsequent periodic wetting of the mortar. The useful
penetration of atmospheric carbon dioxide is but one twenty-fifth inch in interior
plaster work.
Lime-Wood (TiKa). The general name, Tilia europaea> or European lime or
linden, includes several well marked sub-species which are found growing quite
generally over northern Europe. The American bass-wood (Tilia amerlcana) is
similar. The lime sometimes acquires great size and is valuable as a timber tree.
The wood is soft and light and is one of the * white-woods * of commerce. The an-
nual rings are only fairly distinct, even though the pores are very small and dif-
fusely distributed. In longitudinal section neither the figure nor the ray is con-
spicuous. The color is generally light, often a mellow, creamy brown. Linden has
been reported as the wood in a fairly large number of panel paintings of the
German schools. Pliny (XVI, 30) mentions it and describes the tree as growing
in the mountain valleys of Italy.
Linen is made from fibres (see Fabrics and Fibrous Substances) of the flax
plant (Linum usitatissimum) which yield about 8 per cent of these fibres. They
are ultimately 6 to 60 mm. long and 0.012 to 0.026 mm. wide. The cellulose con-
tent is between 70 and 80 per cent. The fibres are obtained from the green bark
by rotting or retting, cleaning, and bleaching. They are very tough, can be
bleached white, and take, more readily than cotton, a variety of colors by dyeing.
Microscopically, linen fibre may be distinguished from cotton, with which it is
most likely to be confused, by the fact that it shows joint-like cross markings and
does not twist, whereas the cotton fibre shows no cross markings and does have
twists (see figure a, p. 231).
Specimens of linen have been found in the villages of the Lake Dwellers and in
other prehistoric remains. The wrappings of most of the Egyptian mummies are
of linen, and fine linens have been made from ancient times. Linen has been woven
successfully in America only in the coarser forms of crash and toweling. Scotland,
Ireland, and Belgium produce the finest linens of commerce today, and Russia,
the largest amount of flax. So common has this material been as a paint support
that it is almost a synonym for canvas, the usual name for a fabric that is painted.
Mahogany, There are two principal varieties of this wood—West Indies
(Swietenia mahagont)^ East coast, tropical America (Swietenia macrophylla)—
and both, among others, are indigenous to tropical parts of America. The former
is harder and darker than the latter, and is a richer red in color. In both varieties
the heart-wood is reddish brown and darkens on exposure to light. The sap-wood
is narrow, and ranges from light brown to white. The growth layers are practically
homogeneous in character, with little variation in pore size, and they are marked
by very thin, light-colored lines. These are the chief marking device, taking the