_Obs._ The first three dry in about 48 hours, and are very useful to
render the joints of wooden casks, cisterns, &c., watertight; also to fix
stones in frames. The last serves to cement glass, wood, and even metal to
each other. A good cement for fixing wood to glass may be made by
dissolving isinglass in acetic acid, in such quantities that it becomes
solid when cold. When applied let it be heated. They all resist moisture
well.
=Cement, Grind'ers'.= _Prep._ 1. From pitch, 5 parts; wood ashes and hard
tallow, of each 1 part; melted together.
2. Black resin, 4 lbs.; beeswax, 1 lb. melt, and add of whiting
(previously heated red hot, and still warm), 1 lb.
3. Shell-lac, melted and applied to the pieces slightly heated. Used to
fix pieces of glass, &c., whilst grinding. The last is used for lenses and
fine work.
=Cement, Hamelin's.= _Syn._ HAMELIN'S MASTIC. From siliceous sand, 60
parts; Bath or Portland stone (in fine powder), 40 parts; lime-marl, 20
parts; litharge, 8 parts; ground together. For use it is mixed up with
linseed oil and used like mortar. When this cement is applied to the
purpose of covering buildings intended to resemble stone, the surface of
the building is first washed with linseed oil.
=Cement, Hensler's.= Litharge, 3 parts; quick-lime, 2 parts; white bole, 1
part (all in fine powder); linseed-oil varnish, q. s. to make a paste.
Used for china, glass, &c. It is very tenacious, but long in drying.
=Cement, H[oe]nle's.= Shell-lac, 2 parts; Venice turpentine, 1 part; fused
together, and formed into sticks. It is used like extemporaneous cement
for glass and earthenware.
=Cement, Hydraulic.= Hydraulic mortars or cements are those which set or
become hard under water. Common lime does not possess this property; but
limestone containing from 8% to 25% of alumina, magnesia, and silica,
yield a lime on burning, which does not slake when moistened with water,
but forms a mortar with it, which hardens in a few days when covered with
water, although it does not acquire much solidity in the air. Puzzolana,
septaria, and argillaceous or siliceous earths, burnt, either with or
without the addition of common limestone, and then ground to powder, form
excellent hydraulic cements. The reniform limestone, commonly called
"cement stone," which is found distributed in single nodules or lenticular
cakes, in beds of clay, is the substance most commonly used in this
country for the manufacture of the cements in question.
"A very good hydraulic mortar is made by slaking lime with water
containing about 2 per cent. of gypsum, and adding a little sand to the
product. The presence of the gypsum tends to delay the slaking of the
lime, and also to harden the substance formed after the slaking.
"If water containing a little lime in solution be added to burnt gypsum, a
very hard compact mass is obtained. This substance is much used as an
imitation marble, as by polishing it with pumice stone, colouring it, and
again polishing with oil, it may be made to resemble natural marble very
closely. Hardened gypsum treated with stearic acid, or paraffin, and
polished, is used as a substitute for meerschaum, which it much
resembles."[238] See GAD'S, HAMELIN'S, and PARKER'S CEMENTS, &c.
[Footnote 238: 'Chemistry, Theoretical, Practical, and Analytical.']
=Cement, Iron.= This cement, which is much used for closing the joints of
iron pipes and similar purposes, is formed of the borings or turnings of
cast iron, which should be clean and free from rust, mixed with a small
quantity of sal-ammoniac and flowers of sulphur. For use, it is stirred
up with just enough water to thoroughly moisten it, and it is rammed or
caulked into the joints with a blunt caulking chisel and hammer, after
which the joint is screwed up by its bolts as tightly as possible. If the
turnings and borings are very coarse they are broken by pounding in an
iron mortar, and the dust sifted off before use. The following are good
proportions:
1. Sal-ammoniac (in powder), 2 oz.; flowers of sulphur, 1 oz.; iron
borings, 5 lbs.; water, q. s. to mix.
2. Sal-ammoniac, 2 oz.; sulphur, 1 oz.; iron borings, 12 lbs.; water, q.
s. to mix.