52 ANNUAL RECORD OF SCIENCE AND INDUSTRY. 



carbonic acid, chemical reaction on the exposed joortion, with 

 rapid oxidation, takes place immediately. 



In reference to the fact, first published by Berzelius, that 

 caustic alkalies prevent the oxidation of iron, he remarks, as 

 the result of special experiments on this subject, that the car- 

 bonates and bicarbonates of the alkalies possess the same 

 property as their hydrates ; and that i an iron blade be half 

 immersed in a solution of such carbonates, they exercise such 

 a preservative influence on that portion of the bar which is 

 exposed to the atmosphere or common air (oxygen and car- 

 bonic acid) that it does not oxidize even after a period of 

 two years. 1 A, March 3, 98. 



HYDEATE OF CHLOEAL FOE EEDUCING METALS. 



Hydrate of chloral may in many cases, according to a Ger- 

 man pharmaceutical journal, be conveniently applied to the 

 reduction of precious metals. For this purpose a solution of 

 gold, platinum, etc., is mixed with hydrate of chloral and an 

 excess of caustic potash or soda, and the whole heated to- 

 gether. After boiling for about one minute the reduction is 

 complete, and the precipitate is easily washed. In the case 

 of silver the action is especially satisfactory, but solutions of 

 salts of mercury are not reduced. 14 (7, 1871, vi., 513. 



EEDUCTION OF NATIVE SULPHIDES. 



Native sulphides of metals often occur of much value in a 

 metallurgical point of view, but which can not be reduced in 

 consequence of the great scarcity of fuel. Dr. Kopp, in a re- 

 cent paper, mentions the results of a series of experiments 

 upon such substances, for the purpose of ascertaining wheth- 

 er certain cheap and abundant chemical reagents can be made 

 to act upon the minerals in question (without at the same 

 time affecting their gangue), so as to bring them into a con- 

 dition fit for being readily converted into metals. The re- 

 agents named as suitable for the purpose in question are 

 common salt, chloride of iron, and hydrochloric acid. In this 

 paper it is stated that the most economical method of ex- 

 tracting the small quantity of copper present in previously 

 burned pyrites consists in first exposing the burned substance 

 to heat and moisture, and then pouring over the material a 

 solution of common salt. A small addition of hvdrochloric 



