ON BLACKINC AND POLISHING LEATHER. 179 



A, represents the transverse section of a cylinder of wood whose 

 calibre is accurately formed. 



B, a longitudinal incision, quite through the cylinder. 



The principle by which this mould is worked, depends on the 

 elasticity of the wood. Previously to forming the core, the in- 

 cision at B, is closed by pressure, and the mould is secured with 

 twine ; it is next filled with loam or sand, and then the twine be- 

 ing cut, it springs open, and may be readily removed without dis- 

 turbing the core. Core Box, 



Philadelphia, April 29th. [Am. Mech. Mag, 



On various Compositions for Blacking and Polishing Leather, 



Various compositions are used to give a sort of polish or v?.inish 

 to leather, by being brushed over it. The blacking that has been 

 most generally used for some years past, in France, was composed 

 of the whites of eggs, beaten up with water ; to which were added 

 a little lamp-black, to color it 5 and some sugar, or gum, to render 

 it shining. It was sufficient to spread this mixture over the leather 

 with a brush, and allow it to dry. 



This blacking is very beautiful, and easy to be made and used ; 

 but has its inconveniences : it is not very solid ; heat causes it to 

 scale off; and it is dissolved by the least quantity of water that 

 touches it. Humidity alone is sufficient to cause it to come off, 

 on the least friction. It is now but little used in large towns, as 

 the following superior composition is substituted for it ; viz : 



Ivory Black - . - 350O grammes,* 

 Melasses .... 350O 



Sulphuric Acid - - - 450 



Hydrochloric or Muriatic Acid - 450 



Weak Acetic Acid - - 1700 



Gum Arabic - - - 200 



I^inseed or Olive Oil - - 200 



10,200 

 The sulphuric acid is diluted with six times its weight of water, 

 which must be mixed with some precaution, adding it by degrees, 

 that the temperature may not be too rapidly raised, or there is 

 great risk of breaking the vessel. A mixture is then made of this 

 diluted acid, with the dydrochloric acid and melasses, in a large 

 earthern vessel. The ivory-black, previously mixed with a suffi- 

 cient quantity of water, to make it of a moderately thick consist- 

 ence, is then added by degrees to the acidulous liquid, stirring it 

 all the while, not only for the purpose of disengaging the gas which 

 is generated, but also to prevent the mixture from forming into a 

 mass, or coagulating. When the mixture is well blended together, 

 it is diluted with weak acetic acid, or common vinegar ; and the 

 gum, previously dissolved in four or five times its weight of water, 

 is then added, with the oil. The whole is then again well stirred 



* The gramme is nearly equal to 15 1-2 English grains. 



