314 Wisconsin. Academy of Sciences, Arts, and Letters . 
gas, a yellow hydroscopic substance being fannied and that this 
substance is readily decomposed into gold and fluorine. 
These two experiments give practically what is known of the 
fluoride of gold: 
The activity of the halogens toward other elements is, as a 
rule, inversely proportional to their atomic weights. The first 
member of this group of active elements, fluorine, is certainly 
the most active of all the elements, be they halogens or not; 
yet, as will be demonstrated later, it appears to have little if 
any affinity for gold. 
In studying the chemistry of gold, it should always be borne 
in mind that it is the most inactive of the metals, but the 
relative stability of the most of its salts, notably with the halo¬ 
gens, would appear to make probable the relative stability of 
the compound with the most active of the elements, fluorine. 
On the other hand, we have the marked difference of fluorine 
from the other halogens in the insoluble fluorides of calcium, 
strontium and barium, as contrasted with the very soluble 
chlorides, bromides, and iodides; and the soluble fluorides of 
silver and thallium as compared with the insoluble chlorides, 
bromides and iodides. 
In order to study the relations between fluorine and gold, ex¬ 
periments were conducted with the view of bringing about if 
possible the formation of gold fluoride under various possible 
conditions. 
The first experiment made was a study of the action of hy¬ 
drofluoric acid on the oxide of gold. To this end, oxide of gold 
was prepared by the action of magnesium oxide on a solution 
of chloride of gold and the excess of magnesia removed with ni¬ 
tric acid. The oxide of gold thus obtained was finely divided 
and hence in the most suitable condition to be susceptible to any 
chemical action. This oxide of gold can remain in contact with 
hydrofluoric acid indefinitely or as has been the case, can be 
boiled for weeks with either hydrofluoric acid alone or with a 
mixture of hydrofluoric and nitric acids without suffering any 
change whatever. These experiments have been repeated sev¬ 
eral times but in no case has gold been found to enter into solu¬ 
tion nor has it been possible to detect fluorine in the precipitate. 
