the Carinthian Molybdate of Lead. 333 
sembles the sulphuric solution of molybdic acid in the vicissi- 
tudes of colour which it exhibits by heat and cold. 
The phenomena which heat produces on the solution of 
cobalt in muriatic or nitro-muriatic acid, called sympathetic 
ink, have long engaged the attention of chemists and others, 
but as yet great difficulties have occurred whenever an expla- 
nation has been attempted. 
There can be no foundation for the idea which some have 
had, that the green colour (which characters traced with this 
solution on paper assume when heated) is caused by a tem- 
porary crystallization of the salt, and the disappearance of the 
colour by a subsequent degree of deliquescence ; because any 
quantity of the liquid becomes green when heated. 
The effects caused by heat on the sulphuric solution of mo- 
lybdic acid have therefore induced me to suspect a similar cause 
in the muriatic solution of cobalt; and I believe that heat and 
cold in like manner causes a temporary difference to take place 
in the proportions of oxygen existing in the acid menstruum 
and the oxyde ; and this is the more confirmed when the acid 
is expelled by too great a degree of heat, for then the changes 
of colour are no longer to be observed. 
Heat, it is well known, assists the combination of oxygen 
with the metals, but I do not believe that the abovementioned 
alternate effects of heat and cold have been as yet investigated. 
It is probable that these are not confined to the two in- 
stances which have been adduced, although in other solutions 
they may not be so apparent. The subject is certainly curious, 
and worthy of the attention of chemists, as it would reflect 
much light on the solutions of metals in general. 
When the sulphuric or muriatic solutions of the molybdic 
