THE YOUNG SCIENTIST. 
51 
affects the wood first, and where the break 
always occurs when removed from the earth or 
strained in testing-. 
Hard Colored Cements for Inlaying*. 
■Colored cements are used to give cast g-oods of 
'zinc or brass the appearance of buhl work, and 
to All up the holes made by etching in zinc door 
plates, street numbers, coats of arms, etc. They 
are also, with advantage, employed for making 
(Casting-models of more artistic objects, as well 
as for mosaics on metal ground ; but they may 
!be further found useful in engineering- works 
for isolaters, large ring-s and plates. According: 
to Stach, the following- process gives g-ood re- 
sults : A solution of soluble glass of 33° Baume, 
is mixed with line whitening-, with the addition 
of the materials mentioned below, until it as- 
simies the tenacity of a thick plastic mass, and 
thus different colored cements, hardening- in six 
or seven hours, of considerable strength, and 
very useful for the purposes above quoted, are 
obtained. By adding gray-sulphuret of anti- 
mony a blacls cement is obtained ; this may be 
polished with agate, and has a metallic onyx- 
like luster. Another black cement is prepared 
by mixing- equal parts of sulphuret of antimony 
and iron hlings (finest) with the above soluble 
glass ; but the cement can only be ground. Car- 
bonate of copper, pure chrome green, give 
green; cobalt blue, blue cements. (Ordinary 
wltramarine is not fit for use, because it decom- 
poses and scatters the mass). Bed lead gives 
orange cement, sulphide of cadmium citrine, 
cinnabar brig-lit red, and cochineal-lac violet 
<?ement ; zinc dust and alcoholized iron g-ive a 
brown cement, and powdered mang-anese acts 
ill the same manner. An especially valuable 
g-ray cement, wiiich may be polished with the 
agate to a metallic luster, and used in the repfiir 
of damaged zinc ornaments— whether cast or of 
: sheet zinc— is produced by mixing pure most 
finely-sifted zinc dust with soluble glass. 
Hitherto these mixtures have been used solely 
for imitating- marble, but the cements are also 
of great value in the metal- ware industry. 
Bronzing--L.iquid.— Ten parts of aniline red 
and five parts of aniline purple are dissolved in 
100 parts of 95 per cent, alcohol, on the water-bath, 
and the solution, after the addition of five parts 
of benzoic acid, boiled (for 5-10 minutes) until it 
has changed its greenish color to light bronze- 
brown. Applied with a brush upon leather, metal, 
or wood, the liquid produces a magnificent bronze 
coating. — Bayr. Lid. und G-ewerh. Zeii. 
Mica.— To the microseopist a world of interest 
may bo found in the micas. They frequently con- 
tain between the layers microscopic crystals of 
minerals, some of them, especially with polarized 
light; forming specimens of wonderful beauty. 
Of most minerals, sections for microscopic exam- 
ination must be made by the laborious process of 
grinding and polishing, but in mica we may 
almost say the sections are made by nature, and 
the time required to make one secition of most 
minerals will make at least 100 of mica, and the 
thickness or thinness is a matter of perfect 
control. 
To Color Horn Black.— C. Burnitz.. of Stutt- 
gart, uses the follo^ving method of accomplishing 
this without subjecting the material to a boiling 
heat: The articles, after being made ready for 
polishing, are to be placed in a lye of caustic soda, 
or potassa, till the upper strata of the horn have 
been dissolved to such an extent that the articles 
feel greasy to the touch. With care, even the 
finest tooth-combs may be thus treated. The 
articles are now washed in water, and drawn 
through aniline black, known as the Lucas ani- 
line black, dried slowly, and then washed. The 
light passing through the horn has a deep-brown 
color; but by reflected light the article appears of 
a deep black. 
Water-tig-ht Parchment Paper Bags.— 
These are made by means of chrome-gelatin. 
A 15 per cent, solution of gelatin in water is 
warmed and mixed, in the dark, with a 3-5 pei- 
cent, solution of potassium bichromate. The 
mixture is poured into small black bottles, and 
kept carefully from the light, which would harden 
it and make it insoluble. Before use, the bottle 
is set into hot water, carefully preventing the 
access of daylight. When the cement is melted, 
the edges of the parchment-paper, which, must 
have been wetted, are brushed over with the 
cement, and then rapidly dried in the sun. To 
test them they are filled afterwards with water 
and hung up in frames. Any hole which may be 
discovered is closed by means of the above 
eemGnt.—PJiann. Zeit. 
How to Clean Marble Top Furniture.— 
It may be of some value to housekeepers who 
have marble-top furniture, to know that the com- 
mon solution of gum arable is an excellent ab- 
sorbent, and will remove dirt, etc., from marble. 
The method of applying it is as follows: Brush 
the dust off the piece to be cleaned, then apply 
with a bjuish a good coat of gum arable, about 
the consistency of thick office mucilage, expose it 
to the sun or dry wind, or both. In a short time it 
will crack and peel off. If all the gum should not 
peel off, wash it with clean water and a clean 
cloth. Of course, if the first application does not 
have the desired effect it should be applied again. 
Another method of cleaning marble is to make a 
paste with soft soap and whiting, wash the mar- 
ble with it, and then leave a coat of paste upon it 
for two or three days. Afterw^ards wash off with 
warm (not hot) water and soap. 
