XII. ] ORIGIN OF METALLIFEROUS DEPOSITS. 237 



APPENDIX. 



ON IODINE AND GOLD IN SEA-WATER. 



AFTER the above lecture was delivered, appeared the results of 

 the researches of Sonstadt on the iodine in sea-water, which were 

 published in the Chemical News for April 26, May 17, and May 

 24, 1872. According to him, this element exists in sea- water, under 

 ordinary conditions, as iodate of calcium, to the amount of about one 

 part of the iodate in 250,000 parts of the water. This compound, 

 by decaying organic matter (and by most other reducing agents), is 

 changed to iodide, from which, apparently by the action of carbonic 

 acid, iodine is set free, and may be separated by agitating the water 

 with bisulphide of carbon. The iodine thus liberated from sea- 

 water by the action of dead organic matters, however, slowly de- 

 composes water in presence of carbonate of calcium, and is re- 

 converted into iodate, the oxygen of the air probably intervening 

 to complete the oxidation, since, according to Sonstadt, iodides are 

 readily converted into iodates under these conditions. He finds 

 that the insolubility of the iodides of silver and of copper is so great 

 that by the use of salts of these metals iodine may be separated 

 from sea-water, without concentration, provided the iodate of cal- 

 cium has first been reduced to iodide. By this property of iodine 

 and its compounds to oxidize and be oxidized in turn, Sonstadt 

 supposes them to perform the -important function of consuming the 

 products of organic decay, and so maintaining the salubrity of the 

 ocean's waters. Their action would thus be very similar to that of 

 the oxides of iron, as explained in the lecture. 



Still more recently the same chemist has announced that the sea- 

 water of the British coasts contains in solution, besides silver, an 

 appreciable amount of gold, estimated by him at about one grain to 

 a ton of water. This is separated by the addition of chloride of 

 barium to the water, apparently as an aurate of baryta adhering to 

 the precipitated sulphate, which yields by assay an alloy of about 

 six parts of gold to four of silver. Other ways have been devised 

 by him for separating these metals from their solution in sea- water. 

 The agent which keeps the gold of the sea in a soluble and oxidized 

 condition is, according to Sonstadt, the iodine liberated by the 

 reaction already described. The views maintained by Lieber, 



