Chemical Science. 619 



Sulphur and saltpetre mixed with charcoal diminish its absorbing 

 power and tendency to inflame *. 



9. POWER OF CARBON TO DESTROY THE BITTERNESS OF CERTAIN 



BODIES. 



M. DUBURGA observed that charcoal destroyed the bitterness of a 

 tincture of gentian root, whilst it had no action on that of the cen- 

 taury ; in consequence of which observation, Dr. Kopff made many 

 experiments on different bitter substances, and found great varieties 

 of action. Each experiment was made with two ounces of distilled 

 water, twenty grains of bitter extract of the particular plant, and 

 about sixty grains of the recently-pulverized charcoal ; they were 

 digested at temperatures from 78 to 86 F., and examined at inter- 

 vals, being compared with similar solutions without the charcoal. 

 Wormwood, centaury, gentian, quassia, were not changed ; orange- 

 peel, camomile, yarrow, soapwort, and Iceland moss, lost all their 

 bitterness. Endive, rhubarb, &c., &c., were nearly deprived of their 

 bitterness. 



When animal charcoal, freed from phosphate of lime, &c., by 

 digestion in muriatic acid, was used in place of vegetable charcoal, 

 similar results were obtained f. 



10. METHOD OF PREPARING SELENIUM FROM THE SULPHURET.- 

 (By M. Magjius.) 



THE best manner of preparing selenium from its compound with 

 lead, consists, according to Professor Mitscherlich, in fusing it with 

 an equal weight of nitre ; this method being, however, inapplicable 

 to the obtaining of the metal from its sulphuret, Berzelius has pro- 

 posed to use caustic potash instead of nitre, a process which is, how- 

 ever, too laborious and too expensive, particularly in those cases 

 where the quantity of selenium is very small, as, for instance, in the 

 sulphuret obtained during the manufacture of sulphuric acid. The 

 following method will, then, be found preferable. The sulphuret 

 being powdered, and mixed with eight times its weight of the per- 

 oxide of manganese, is heated in a retort; the sulphur becomes 

 changed into sulphurous acid, and the peroxide into the protoxide, 

 and at the neck of the retort a sublimate forms, which consists of 

 pure selenium. If manganese has been employed in excess, the sub- 

 limate becomes oxidized after the complete evolution of sulphurous 

 vapour, and forms crystallized selenious acid. The sulphurous acid 

 is passed through water, from which the small quantity of selenious 

 acid which might possibly be carried over, is precipitated in a metal- 

 lic state. The sublimate will always be found to contain some sul- 

 phur, from which it, however, is easily separated, by fusing it re- 

 peatedly with the peroxide of manganese, or with caustic potash. 



* Ami. de Chiui., xlv. p. 73. f Journ. de Phann., 1831, p. 172. 



