PROFESSOR CAliVERT ON THE OXIDES, &c., OF LEAD. 131 



CETSTALLIZED PINK OXIDE — ^ACTION OF SODA ON THE 

 HYDRATE. 



When a solution of boiling caustic soda, of specific gravity 

 1 '454 to 1*375, is saturated with hydrate of oxide of lead 

 and left to cool, two crystallized oxides are deposited ; one 

 of them is white, and has been examined by Mr. Payen, the 

 other is pink, and crystallizes in rectangular prisms. This 

 oxide, heated to about 750°, augments in volume, and de- 

 crepitates in the same manner as the black oxide of tin, 

 discovered by Mr. Fremy, Whilst this phenomenon is pro- 

 ceeding, a small quantity of water, about one per cent., is 

 given off, owing to a small amount of interposed water, as 

 is remarked in the chloride of sodium and other salts. 

 If the oxide is then left to cool, the intensity of its colour 

 is slightly changed; but if heated to redness and cooled, it be- 

 comes yellow, and has the crystalline form presented by the 

 pink oxide. I took advantage of the fact, that this protoxide 

 of lead is slowly dissolved by acids, to separate it from the 

 white, and accordingly treated them by acetic acid, which 

 readily dissolved the white and left the pink, which after 

 being washed was quite pure. Strong or weak nitric 

 acid dissolves this oxide slowly, owing doubtless to its 

 being crystallized and anhydrous. Its specific gravity is 

 from 9" 15 to 9- 18, and when pulverized it gives a yellow 

 Orange powder, similar to that which real massicot produces. 



23-446 oxide lost 1-683 of oxygen, or 7"179 per cent. 

 Oxide of lead, 92-821 „ 



100-000 

 Its analysis gave me, by taking into account the interposed 

 water, the numbers which represent the protoxide of lead. 



AMORPHOUS RED OXIDE. 



Instead of taking the concentrated solution of caustic soda^ 

 I melted the solid alkali, and threw into it some hydrate 



