138 Laboratory Arts 



one-twentieth its volume of strong nitric acid. Keep well 

 corked and in the dark. 



Chatterton's Compound. This is purchased ready 

 made ; it is used for cementing dissimilar substances, iron and 

 wood, leather and wood, etc., though it makes a water-tight 

 joint on a glass cell well, if applied to ground surfaces. The 

 method of application is to heat the surfaces to be joined, 

 melt the Chatterton at the Bunsen flame (not ordinary gas 

 flame) spread a little over the surface, heat again, and spread 

 with a splint of wood until the whole surface to be cemented is 

 covered with a thin layer of cement. The second surface is 

 similarly treated, the two heated fairly strongly, and well 

 pressed together in a vice or under a heavy weight if 

 possible. When cool, the joint is trimmed. 



A good cement to take the place of " Chatterton " is made 

 by melting a quantity of flake shellac in an iron ladle and 

 stirring in twenty per cent, of " oil of cassia." 



Shellac. Shellac is one of the most useful of cements ; it 

 may be used alone, in the same way and for the same purposes 

 as Chatterton's compound, or it may be dissolved in methy- 

 lated spirit and used as a varnish, or in stronger solution used 

 direct, as a cement. In any case the object should be cleaned, 

 dried, and heated before the application of the shellac. 



Cement for Celluloid. Dissolve some celluloid scrap- 

 ings in acetone. The liquid will clear upon heating slightly, 

 and is then ready for use. 



Vulcanite shavings dissolved in sulphuric ether will also 

 answer the same purpose. 



Miscellaneous. A useful cement for fixing brass rings 

 to glass cylinders, etc., is made by mixing five parts resin, 

 one part beeswax, one part red ochre, at a high temperature, 

 and allowing to cool. The cement is applied hot, in the same 

 way as Chatterton's compound. 



For fixing pestle handles nothing is better than melted 

 resin, as it appears able to withstand the percussion shocks 

 better than any other substance. A little teased-out twine or 

 hempen rope should be loosely wrapped round the pestle 

 stump, to prevent the resin cracking. 



