CEMENTS. 



66.5 



fncnti. CEMENTS. This term ia of very extensive sig- 

 * *Y^*' nificaiion, comprehending every substance employed 

 for the purpose of connecting together other sub- 

 stances. It, therefore, comprises the whole of those 

 substances used by chemists to close the joinings of 

 chemical vessels ; to repair flaws, or to coat the ex- 

 terior parts of those vessels which are subjected to 

 the action of heat. 



Occasionally cements are employed for coating ves 

 els that are to be exposed to a very considerable 

 heiit ; and the process is called loricalion, or coating. 

 Iron furnaces are generally coated in the inside, to 

 prevent the destruction consequent on continued ex- 

 posure to the action of the fire. 



For the common purposes, such as to prevent the 

 escape of steam, the vapours of alcohol, or of any 

 other liquid which is not corrosive, slips of bladder 

 which have been soaked in warm water until they 

 become adhesive, answer extremely well for glass ; 

 and paper, with' paste, for metallic tubes. A solu- 

 tion of gum arabic, or the white of an egg, increases 

 the adhesiveness. 



Lintseed meal, or almond paste, well beaten up with 

 water, so as to form a pretty dense paste, form a 

 very firm lute for common purposes. Cut it is unfit 

 for a higher temperature than that of boiling wa- 

 ter, or for the continued action of acrid gases. It 

 will, however, confine ammoniacal and the acid gases 

 Sufficiently long for the usual experiments Milk, 

 lime water, or a weak solution of glue or size, im- 

 proves it considerably. 



Many very impervious lutes are made with quick- 

 lime as a basis. This quicklime is reduced into a 

 ductile mass by an admixture of some mucilaginous 

 matters. As combinations of this sort are obviously very 

 numerous, we shall give only a very few of them. 



Take some lime that has been perfectly burnt, 

 dip it into water, and allow it to fall into a very fine 

 powder, which it will readily do if the calcination 

 has been complete, and then beat this powder very 

 carefully with equal parts of the white of eggs and 

 of water, to the consistence of thin paste. The 

 lute thus formed should be laid on thin slips of cloth, 

 and applied to the junction of the vessels to be luted. 

 If a small quantity of the powdered lime be sprink- 

 led upon the slips of cloth, the junction will be 

 rendered more complete. The same lute may be made 

 in a simpler way ; take thin slips of cloth, moisten- 

 ed with the white of eggs, and sprinkle them over 

 with the powdered lime. This last mode has the ad- 

 vantage of drying with great rapidity. 



Lime mixed with dissolved glue also forms a very 

 excellent cerrent ; and, when the white of eggs are 

 added, the hit iVane is then formed. The above lutes, 

 however, do not resist the action of water, though 

 they are quite impervious to vapours. 



Very poor skimmed milk cheese, rubbed down to 

 the consistence oi" thick soup, with the addition of 

 lime, makes a good lute. 



Paris plaster, mixed with any mucilaginous mat- 

 ters, is useful as a cement. Sometimes other substances 

 are add* d, as clay, flour, red oxide of iron, &c. 



The calcareous lutes become extremely liurd, and 

 it is difficult to free vessels from tiiem. They are 

 therefore not proper where delicate vessels winch are 

 to be preserved are emplo)ed. In large works, or 

 in experiments where large vessels are used, it is well 

 to have a quantity of them at hand, as they are very 



VOL. V. PART II. 





convenient for stopping up any accidental crack, 

 either of the lute originally applied, or of the vessel 

 itself. It may be al&o observed, that these lutes will 

 not confine acrid vapours for any length of time ; 

 but for every other purpose they are admirably a- 

 dapted, particularly where heat is necessary. 



The fat lute, as it is commonly called, is of very 

 general use, but peculiarly so when exposed to 

 acid vapours. It also possesses another advantage, 

 that of being never hardened to an inconvenient de- 

 gree. Any good clay, such as pipe clay, or pot- 

 ter's clay, perfectly dry, must be reduced to a very 

 fine powder, and then gradually beaten into thick 

 paste with drying linseed oil. The beating must be 

 continued until the mass ceases to adhere to the pes- 

 tle. It improves from being kept in a covered ves- 

 sel, in a cool situation. It becomes quite fit for use 

 by being beaten up again for a few minutes with a 

 few drops of limserd oil. 



The above may be considered as constituting by 

 far the most generally useful lutes for connecting 

 chemical apparatus together; there are, besides these, 

 another class of lutes, which is of high value to the 

 practical chemist, and of some of them we shall now 

 give a short account. As glass vessels, when sub- 

 jected to a considerable temperature, are liable to 

 melt, they are frequently coated with lutes, which 

 protect them, and obviate the inconveniences which 

 would result from complete exposure. Earthen ves- 

 sels being naturally porous, are apt to allow any vo- 

 latile matters contained in them to escape ; this is also 

 remedied by similar means. To secure glass vessels, 

 sand is mixed with as much clay as binds the whole 

 mass together, a. id is beaten up with any fibrous mat- 

 ter, which gives at) additional degree of mechanical 

 security. Windsor loam answers well ; but an equally 

 useful cement may be formed from an admixture of 

 sand and coarsely ground potter's ware ; to which 

 horse dung, chopped straw, chaff, horse or cow's 

 hair, or tow, may be added, in such proportions as 

 will render the whole mass perfectly ductile. An 

 ounce of hair is said to be sufficient for five pounds 

 of the earthy mixture. The mass should be beaten 

 together with great care, so as to diffuse the hair 

 throughout the whole of it. It may be then applied 

 to the surface, to be coated, either in the dry state, 

 or by repeated dippings into a thick mixture of the 

 mass with water. If the coating be smeared with 

 lintseed oil after it is thoroughly dry, it will be less 

 liable to crack. 



As a coating for earthenware vessels, various com- 

 pounds may be formed of a variety of fluxes, mixed 

 into a thin paste with clay and lime. One ounce of 

 borax dissolved in a pint of boiling water, added to 

 as much lime as will form a thin paste, will be an ex- 

 cellent coating of this kind. Aftet this has been ap- 

 plied to the earthen vessel, and has become properly 

 dry, a lute of lime and linseed oil should be laid over 

 the whole. When it is completely dry, the vessel is 

 fit for use. By renewing the last lute, the vessel may 

 be used several times with safety. This preparation 

 has been chit- fly recommended as a coating for vessels 

 in which phosphorus is prepared. 



It IB frequently necessary to lute the covers of cru- 

 cibles, so as to exclude any communication with the 

 external air ; and it is an object of importance, to 

 h ive a lute thut can bear a high temperature. An 

 excellent compound of that kind is formed by borax 



