104 M. Lewenau on Selenium. [Aug. 



buried allows us to conclude that this action, though slow, has 

 been sufficient to produce such marked effects of oxidation. 



The same reasoning is applicable to many other phenomena, 

 which are daily occurring before our eyes. It is for this reason, 

 for instance, that we are obliged to attach the copper sheeting of 

 our ships with copper nails, and not with nails made of iron, that 

 the contact of two dissimilar metals may not give rise to an 

 electrical action, which, by the decomposition of the water, 

 would speedily determine the oxidation of the iron, the copper 

 in this case being negative. 



Article V. 



Extraction of Selenium from the sulphureous Deposits left, in the 

 Manufacture of Sulphuric Acid from Pyrites. Translated 

 from the German of M. Lewenau, by M. Robinet.* 



M. Lewenau has presented a monograph on selenium to the 

 Societe de Pharmacie. Having been desired to extract what- 

 ever is interesting and new in the Memoir, I have been occu- 

 pied in examining the work. It gives a complete history of the 

 discovery, properties, and modes of obtaining selenium, con- 

 densing in one view all that is known of this substance, from the 

 several accounts that have been published respecting it, since 

 M. Berzelius discovered it in 1818. But independently of what 

 he has borrowed from others, M. Lewenau's treatise contains 

 observations which belong to himself alone, and have appeared 

 nowhere else ; they deserve the attention of chemists in general. 

 M. Lewenau has been principally occupied with the methods of 

 preparing selenium, and the following is the process he has 

 adopted. I give it exactly as he has detailed it. 



" One pound of the deposit was introduced into a tubulated 

 retort, of the capacity of four pints, taking care that none should 

 adhere to the sides ; the retort was placed on the sand-bath, and 

 a large globular receiver, united by a "Woulf's tube to a flask full 

 of water, adapted to it. The apparatus being luted, the acid 

 was introduced, in the proportion of eight pounds of muriatic 

 acid, sp. gr. 1-200, to lour pounds of nitric acid, sp. gr. l - 500. 

 To avoid the effects of the violent action which suddenly takes 

 place, only a fourth part of the acid was introduced at first, and 

 carefully poured over the bottom of the retort by means of a 

 funnel with a long neck. The mass immediately began to 

 heat and swell up, and to give off a considerable quantity 

 of red vapours. The liquid assumed a. dark-grey colour, and 



" From the Journal lie Phanaacic. 



