CEMENTS and lutes. Under this ar ticle may be mentioned the receipts for preparing some of the most useful sub stances of this kind that are required in common chemical operations. The uses of lutes and cements are either to close the joinings of chemical vessels to pre vent the escape of vapours and gases dur ing the processes of distillation, sublima tion and the like, or to protect vessels from the action of the fire, which might crack, or 'fuse, or calcine them ; or sometimes to repair flaws and cracks, and for a variety of other smaller purposes.
From the vast variety of receipts for lutes and cements of different kinds, the following may be selected, which will an swer most of the purposes of the expe rimental chemist. To prevent the es cape of the vapours of water, spirit, and liquors not corrosive, the simple applies. tion of slips of moistened bladder will an swer very well for glass, and paper with good paste for metal. Bladder, to be ve ry adhesive, should be soaked some time in water moderately warm, till it feels clammy ; it then sticks very well : if smeared with white of egg, instead of wa ter, it adheres still closer. Another ve ry convenient lute is linseed meal, mois tened with water to a proper consistence, well beaten, and applied pretty thick over the, joinings of the vessels. This immediately renders them tight, and the lute in some hours dries to a hard mass. Almond paste will answer the same pur pose. The use of the above lute is so ex tensive, that no other is required in clos ing glass vessels in preparing all com mon distilled liquors ; and it will even keep in ammonia, and acid gases, for a longer time than is required for most ex perimental purposes. It begins to scorch and spoil at a heat much above boiling, and therefore will not do as a fire-lute. It is still firmer, and dries sooner, when made up with milk, or lime-water, or weak glue. A number of very cohesive cements, impervious to water and most liquids and vapours, and extremely hard when once solidified, are made by the union of quick-lime with many of the ve getable or animal mucilaginous liquors. The variety of these is endless. We may first mention the following, as it has been extensively employed by chemists for centuries. Take some whites of eggs with as much water, beat them well to gether, and sprinkle in sufficient slaked lime to make up the whole to the con sistence of thin paste. The lime should
be slaked by being once dipped in water, and then suffered to fall into powder, which it will do speedily, with great emis sion of heat, if well burnt. This cement should be spread on slips of cloth, and applied immediately, as it hardens or sets very speedily. While hardening it may be of use to sprinkle over it some of the lime in fine powder. This cement is of ten more simply and as conveniently ma naged, by smearing slips of linen on both sides with white of egg, and when appli ed to the joining of the vessels, shak ing some powdered lime over it ; it then dries very speedily. Another lute of the same kind, and equally good, is made by using a strong solution of glue to the lime, instead of the white of egg : it sets equal ly soon, and becomes very hard. A mix ture of liquid glue, white of egg, and lime,makes the fold' ane, which is so firm, that broken vessels united with it are al most as strong as when sound. None of these lutes, however, will enable these vessels to hold liquids for any great length of time. Milk or starch, with lime, make a good but less firm lute. A very firm and singular lute of this kind is made by rubbing down some of the poor est skimmed-milk cheese with water, to the consistence of thick soup, and then adding lime, and applying as above : it answers extremely well. Lime and blood, with a small quantity of brick-dust, or broken pottery, stirred in, is used in some places as a very good water-ce ment for cellars and places liable to damp.
All the above-mentioned cements, with lime, become very hard by drying, inso much that they cannot be separated from glass vessels without the help of a sharp knife and some violence ; and hence deli cate vessels and long thin tubes, cement ed with it, are apt to break when the ap paratus is taken down, and sometimes even by the mere force of contraction in setting. It is a great advantage, how ever, that they may be applied imme diately to any accidental crack or failure of the lute already on, notwithstanding a stream of vapour is bursting through ; and in large distillations it is of advantage always to have some of the materials at hand.