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JOURNAL, E.A.S. (CEYLON). [VOL. XIX. 



edges of the holes downwards. The whole are now placed 

 in a glass or earthenware dish and a weight is put on the top, 

 so that each zinc plate is not only strongly in contact with the 

 edges of the holes in the plate below, but also presses on the 

 coins which lie between. Over the whole is poured a 5 per 

 cent, solution of caustic soda (sodium hydrate 2 oz., water 

 1 quart), which converts the zinc and copper into a galvanic 

 battery. In twenty-four hours the process is complete (unless 

 the coins are very much incrusted, when a longer time is re- 

 quired) , and the coins may be taken out and at once thoroughly 

 rinsed in water. They should then be placed in a dish and 

 hot water poured over them. This washing should be re- 

 peated four or five times, and the coins should be allowed to 

 soak for a day, after which they can be cleaned by rubbing 

 with soft sifted brickdust and water, grit being carefully 

 excluded. They should then be thoroughly dried by hot 

 sunlight (tropical) or by placing in the oven for a few minutes. 



When in the solution the bottom zinc plate should rest on 

 supports (not on the bottom of the dish), so as to allow the 

 dissolved matter to settle. 



Everything which has been in caustic soda should be 

 rinsed before handling. 



The solution and zinc cannot be used twice, but are so cheap 

 that this does not matter. Prolonged immersion does not 

 seem to damage coins. 



Single coins or small batches can be treated easily by 

 merely wrapping them in zinc tapes and immersing. The 

 zinc should be the thinnest procurable. 



