150 Remarks on Priestley’s Analysis ° 
temperature of the atmosphere. ( Gren, § 2764 
and seq.) 
He says, that finery cinder and massicot are si- 
~ milar substances.—I admit the analogy. They are ~ 
both oxyds of an inferior degree of oxydation; per- 
haps of the same degree. As massicot, therefore, 
has the property of receiving a higher degree of oxy- 
dation,* he cannot deny this property to finery 
cinder. The rust of iron is also converted into 
finery cinder by the abstraction of a portion of its 
oxygen: which may be accomplished by heating it in 
close vessels, either alone,t or (more easily) with sub- 
stances which have a greater affinity with oxygen than 
the iron has. 
* In the preparation of minium, the lead is first con- 
verted into massicot, by exposing it toa red heat with 
access of air. It is afterwards washed, in order to separate 
any metallic particles it may contain; and the pure massi- 
cot when dry is spread on iron plates, and roasted in a 
moderate heat, till it has acquired the proper colour for 
minium. 
+ It may appear extraordinary, since part of the oxygen 
of some metallic oxyds (such as the red oxyds of iron and 
lead and the black oxyd of manganese), can be expelled 
by a certain degree of heat, that the whole of it cannot be 
expelled by the same means. It is evident that oxygen 
has a greater attraction to iron, lead, and manganese, than 
to caloric, since it leaves this and combines with those 
metals, When, therefore, the reverse takes place, the de- 
composition of these metallic oxyds can only be partial: 
the same as the decomposition of some sulphates by the 
