CEMENTS. Substances capable of taking the liquid form, and of being in that state applied between the surfaces of two bodies, so as to unite them by solidifying. They may be divided into two classes, those which are applied through the agency of a liquid men struum, such as water, alcohol, or oil, and those which are applied by fusion with heat.
The diamond cement for uniting broken pieces of china, glass, &c., which is sold as a secret at an absurdly dear price, is composed of isinglass soaked in water till it becomes soft, and then dissolved in yroof spirit, to which a little gum resin ammoniac, or galbantn, and resin mastic are added, each previously dis solved in a minimum of alcohol. 'When to be applied, it must be gently heated to liquefy it ; and it should be kept for use in a well-corked vial. A glass stop per would be apt to fix so as not to be removable. This is the cement em ployed by the Armenian jewellers in Turkey for glueing the ornamental stones to trinkets of various kinds. When well made it resists moisture.
Shellac dissolved in alcohol, or in a solution of borax, forms a pretty good cement. White of egg alone, or mixed with finely sifted quicklime, will answer for uniting objects which are not ex posed to moisture. The latter combina tion is very strong, and is much em ployed for joining pieces of spar and marble ornaments. A similar compo sition is used by copper-smiths to secure the edges and rivets of boilers ; only bullock's blood is the albuminous matter used instead of white of egg. Another cement in which an analogous substance, the curd or caseum of milk is employed, is made by boiling slices of skim-milk cheeses into a gluey consistence in a great quantity of water, and then incor porating it with quicklime on a slab with a muller, or in a marble mortar. When this compound is applied warns to broken edges of stoneware, it unites them very firmly after it is cold.
A cement which gradually indurates to a stony consistence may be made by mixing 20 parts of clean river sand, two of Enlarge, and one of quicklime, into a thin putty with linseed oil. The quick lime may be replaced with Enlarge, When this cement is applied to mend broken pieces of stone, as steps of stairs, it acquires after some time a stony hard ness. A similar composition has been
applied to coat over brick walls, under the name of mastic.
The iron-rust cement is made of from 50 to 100 parts of iron borings, pounded and sifted, mixed with one part of sal ammoniac ; and when it is applied, moistened with as much water as will give it a pasty consistency. Formerly flowers of sulphur were used, and much more sal-ammoniac in making this ce ment, hut with decided disadvantage, as the union is effected by the oxydize ment, consequent expansion, and solidi fication of the iron powder, and any he terogeneous matter obstructs the effect. The best proportion of sal-ammoniac is, I believe, one per cent of the iron bor ings. Another composition of the same kind is made by mixing 4 parts of fine borings, or filings of iron, 2 parts of potter's clay, and 1 part of pounded pot sherds, and making them into a paste with salt and water. When this cement is allowed to concrete slowly on iron joints, it becomes very hard.
For making architectural ornaments in relief, a moulding composition is formed of chalk, glue, and paper paste. Even statues have been made with it, the paper aiding the cohesion of the mass.
Mastics of a resinous or bituminous nature which must be softened or fused by heat are the following : Mr. S. Varley's consists of sixteen parts of whiting sifted and thoroughly dried by a red heat, adding when cold a melted mixture of 16 parts of black resin and 1 of bees'-wax, and stirring well during the cooling.
Mr. Singer's electrical and chemical apparatus cement consists of 5 lbs. of resin, 1 of bees'-wax, 1 of red ochre, and two table-spoonsful of Paris plaster, all melted together. A cheaper one for cementing voltaic plates into wooden troughs is made with 6 lbs. of resin, 1 pound of red ochre, of a pound of plaster of Paris, and # of a pound of lin seed oil. The ochre and the plaster of Paris should be calcined beforehand, and added to the other ingredients in their melted state. The thinner the stratum of cement that is interposed, the strong er, generally speaking, is the junction.