218 Professors Redtenbacher and Liebig 



turbid by caustic ammonia. The lead obtained by reducing 

 this oxide by means of hydrogen, dissolved in nitric acid, with- 

 out leaving any residue. The oxide is therefore pure. 



" The oxide in masses, not in powder, is introduced into a 

 glass bulb blown upon a barometer tube, and in this it is 

 weighed. In order to expel all moisture, the bulb was heated 

 over a spirit-lamp, until the oxide assumed a dark orange red 

 colour, and a stream of dry air was then passed through it, 

 after which it was allowed to cool. The oxide regains its 

 lemon-yellow colour by this treatment, proving that no mi- 

 nium is found, for which indeed the temperature is not suffi- 

 ciently high. The oxide prepared in this manner is very little 

 hygroscopic, so that 13 to li grammes contain at the utmost 

 from 1*5 to 2 millegr. of moisture. 



" The hydrogen gas was evolved from distilled zinc and 

 sulphuric acid, and was, previous to entering the bulb, con- 

 ducted through a solution of oxide of lead in caustic potass, 

 and also through a tube containing coarsely powdered hydrate 

 of potass. At the commencement of the operation, and until 

 about two-thirds of the oxide were reduced, the temperature 

 was not raised so high as to make the bottom of the bulb red- 

 hot ; when this precaution is neglected beyond certain limits, 

 a portion of the oxide of lead combines with the glass, and is 

 not subsequently reduced. It was on this account that the 

 oxide was introduced in masses, which only touched the glass 

 at a few points ; free access between the pieces was moreover 

 by this method afforded to the hydrogen. The first effect of 

 the hydrogen gas is to convert the oxide into suboxide, owing 

 to which the masses become of a dark gray colour; their 

 form and size are not otherwise changed, although the tempe- 

 rature is higher than is required for their fusion, supposing 

 them to consist of metallic lead. As soon as the glass begins 

 to be red-hot at the bottom, small globules of lead are seen to 

 form, and the whole is gradually converted into fused metallic 

 lead. Of the portions of oxide of lead which were afterwards 

 analysed, only two were obtained by one and the same opera- 

 tion ; all the others were separately prepared, so that a fault 

 in the preparation of the oxide cannot introduce a constant 

 error into all the analyses; this, however, might easily occur 

 if the same specimen of oxide had been employed in all the 

 different analyses. 



