132 PR0FE8S0K CALVEKT ON THE 



of protoxide of lead, which became instantly red, and 

 produced a new isomeric protoxide. To take away the 

 excess of alkali, I washed this oxide with spirit of wine and 

 boiled distilled water. This oxide, dried in vacuo, has the 

 greatest resemblance to red lead ; still it contained no trace 

 of peroxide of lead, as it dissolved readily and entirely in 

 acids ; triturated, it gave a powder similar to the pink oxide ; 

 heated to above 700 degrees, it became of a darker colour, 

 did not decrepitate, and, on being left to cool, assumed a 

 beautiful sulphur colour. 



This oxide retains hygrometric water with the greatest 

 tenacity, therefore great care must be taken in its analysis. 



23*213 of oxide lost 1'667 of oxygen, or 7"18 per cent 

 Oxide of lead left, 92-82 



10000 



I also made an analysis of the oxide, which became yel- 

 low by heat. 



12053 of oxide lost 0864 of oxygen, or 7*17 per cent. 

 Oxide of lead left, 92-83 



100 00 

 These analyses demonstrate that these two oxides are 

 identical, and that the colour which each of them has is 

 caused by the particular arrangement of their molecules, 

 which, by acting differently on light, causes them to appear 

 to us either red or yellow. This molecular change is due, 

 in my opinion, to the effect of heat, and not to a chemical 

 cause ; therefore it appears probable that the colour which 

 massicot takes in becoming red lead, results from the same 

 cause, and is not owing, as is generally believed, to the 

 presence of a small quantity of binoxide of lead, or to the 

 plumbate of protoxide. Moreover, the quantity of this 

 compound in red lead is in too small a proportion to give 

 it its beautiful tint. A fact which substantiates my opinion 

 ig, the instantaneous formation of the above amorphous 

 red oxide, when hydrated white oxide is brought in con- 



