CEMENTS 755 



decided disadvantage, as the union is effected by the oxidisement, consequent expan- 

 sion and solidification of the iron powder, and any heterogeneous matter obstructs the 

 effect. The best proportion of sal-ammoniac is, one per cent, of the iron borings. 

 Another composition of the same kind is made by mixing 4 parts of fine borings or 

 filings of iron, 2 parts of potters' clay, and 1 part of pounded potsherds, 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. Some French statuettes are so made. 



Mastics of a resinous or bituminous nature which must be softened or fused by heat 

 are the following : 



Mr. S. Varley's consists of 16 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 Ibs. of resin, 

 1 of bees'- wax, 1 of red ochre, and 2 tablespoonfuls of Paris-plaster, all melted to- 

 gether. 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 stronger, generally speaking, is the junction. 



Boiled linseed oil and red lead mixed together into a putty are often used by copper- 

 smiths and engineers to secure joints. The washers of leather or cloth are smeared 

 with this mixture in a pasty state. 



The resin mastic alone is sometimes used by jewellers to cement by heat cameos of 

 white enamel or coloured glass to a real stone, as a ground to produce the appearance 

 of an onyx. Mastic is likewise used to cement false backs or doublets to stones to 

 alter their hue. 



Melted brimstone, either alone or mixed with resin and brick-dust, forms a tolerably 

 good and very cheap cement. 



Plumbers' cement consists of black resin 1 part, and brick-dust 2 parts, well in- 

 corporated by a melting heat. 



The cement for coating the fronts of buildings consists of linseed oil, rendered dry 

 by boiling with litharge, and mixed with porcelain clay in fine powder, to give it the 

 consistence of stiff mortar. Pipe-clay would answer equally well if well dried, and 

 any colour might be given with ground bricks or pottery. A little oil of turpentine 

 to thin this cement aids its cohesion upon stone, brick, or wood. It has been applied 

 to sheets of wire cloth, and in this state laid upon terraces, in order to make them 

 water-tight ; but it is little less expensive than lead. 



The bituminous or black cement for bottle corks consists of pitch hardened by the 

 addition of resin and brick-dust. 



In certain localities where a limestone impregnated with bitumen occurs, it is dried, 

 ground, sifted, and then mixed with about its own weight of melted pitch, either 

 mineral, vegetable, or that of coal-tar. When this mixture is getting semifluid, itmay 

 be moulded into large slabs or tiles in wooden frames lined with sheet iron, previously 

 smeared over with common lime-mortar, in order to prevent adhesion to the moulds, 

 which, being in moveable pieces, are easily dismounted so as to turn out the cake of 

 artificial bituminous stone. This cement is manufactured upon a great scale in many 

 places, and used for making Italian terraces, covering the floors of balconies, flat 

 roofs, water reservoirs, water conduits, &c. When laid down, the joints must be well 

 run together with hot irons. The floor of the terrace should be previously covered 

 with a layer of Paris-plaster, or common mortar, nearly an inch thick, with a regular 

 slope of one inch to the yard. Such bituminous cement weighs 144 pounds the cubic 

 foot; or a foot of square surface, one inch thick, weighs 12 pounds. Sometimes a 

 second layer of these slabs or tiles is applied over the first, with the precaution of 

 making the seams or joints of the upper correspond with the middle of the under 

 ones. Occasionally a bottom bed, of coarse cloth or grey paper, is applied. The 

 larger the slabs are made, as far as they can be conveniently transported and laid down, 

 so much the better. For hydraulic cements, see HYDRAULIC CEMENTS and MORTAR. 



An excellent cement for resisting moisture is made by incorporating thoroughly 

 eight parts of melted glue, of the consistence used by carpenters, with four parts of 

 linseed oil, boiled into varnish with litharge. This cement hardens in about forty- 

 eight hours, and renders the joints of wooden cisterns and casks air- and water-tight. 

 A compound of glue with one-fourth its weight of Venice turpentine, made as above, 

 serves to cement glass, metal, and wood to ono another. The gluten of wheat, well 

 prepared, is also a good cement. White-of-egg with flour and water well mixed, 

 and smeared over linen cloth, forms a ready lute for steam joints in small apparatus. 



White lead ground upon a slab with linseed-oil varnish, and kept out of contact of 



so a 



