Useful Cements 137 



With some cements, such as cementium, which has the property 

 of setting into a hard mass upon exposure to air, it is possible 

 to " build in " spaces between materials to be cemented, but 

 this is not possible with glue, or other examples of true 

 cements. 



The kind of cement chosen, therefore, will depend upon 

 the nature of the work to be attempted. 



Acetic Acid Cement. 1 For broken glass, porcelain, 

 or similar hard substances, which break with a clean surface. 

 Take a quantity of gelatine, and allow it to soak in cold 

 water until it has absorbed about its own volume. Add about 

 half the total volume of glacial acetic acid, heat until homo- 

 geneous, when it will be ready for use. If in cooling it does 

 not set into a stiff jelly, add more gelatine and heat again. 

 The cement is applied with a wood splint, to the warmed 

 surfaces, previously cleaned and dried. When cemented, the 

 article is squeezed together, tied round with string if possible, 

 and left for twenty-four hours, when the excess of cement may 

 be scraped off, or removed with a cloth soaked in hot water. 



Treacle Glue. For ground surfaces. Make up a quantity 

 of strong glue, by soaking ordinary glue overnight in cold 

 water, pouring off the remaining water, and melting the glue by 

 immersing the jar containing it in a saucepan of boiling water. 

 Add to this one-fifth its weight of black or common treacle, 

 and stir well. The glue is applied hot, and on cooling a firm 

 and watertight joint is formed. The mixture does not keep. 



Bichromate Glue. For glass or porcelain joints which 

 have to withstand the action of hot water. Prepare a quantity 

 of strong glue as before, and add to it, when melted, one-tenth 

 of the weight of powdered bichromate of potash. Keep at a 

 high temperature until the bichromate is dissolved, when the 

 glue will be ready for use. Exposure to light helps the 

 cement to harden. 



Liquid Glue. For leather and glass, leather and iron, 

 leather and wood, etc. Add to a strong solution of glue about 



1 For mending broken glass apparatus of large size, after cementing use 

 may be made of the gummed linen strips sold for the repair of music, 

 subsequently painting the strip with shellac varnish. 



