84 
ON WHITE LEAD. 
short a time when employed as a pigment, and Mulder there- 
fore believes that the hydrated oxide is the principal cause of 
this change of color, as sulphuretted hydrogen affects the car- 
bonate less than the hydrate. That this view is correct is 
shown from the great tendency to become yellow possessed 
by the compound containing one atom each of carbonate and 
hydrate. (See the commencement of this essay.) The ordi- 
nary carbonates will absorb a certain quantum more of carbo- 
nic acid, but never so much as to expel all the water and form 
a neutral salt. This curious fact seems to show that there is 
a stronger affinity between the hydrate and carbonate than 
between carbonic acid and oxide of lead, to form a neutral 
salt, and from all the above processes it is evident that there 
is a superior tendency to form a compound, consisting of two 
atoms of carbonate and one atom of hydrate. 
It appears then from the preceding, that we are acquainted 
with at least three distinct varieties of white lead. 
Hydrotricarbonate, (P&0 + HO) + (P604-C0 2 ) 
Hydrobicarbonate, (P6 + H0) + 2 (P&O-fCO 2 ) 
Hydrotricarbonate, (P b + H 0) -f 3 (P 6+OC 2 ) 
Journ. Frank. Inst. Jan. 1842. 
