262 FLUORINE. 



with bases, that hydrofluoric acid should be compared with hydro- 

 chloric acid and not with the sulphur compound. It resembles abso- 

 lutely the acid formed from one volume of chlorine and one volume of 

 hydrogen united without condensation. 



Let me now recall to you a much more recent experiment of Gore. 

 This chemist heated fluoride of silver in an atmosphere of hydrogen. 

 Under these conditions he saw the volume of gas double itself; it was 

 apx)arent, then, that hydrofluoric acid was formed by the union of one 

 volume of hydrogen with one volume of the element not yet isolated, 

 fluorine. Furthermore, it was evidently that same element Avhich had 

 left the silver fluoride to unite with hydrogen and to generate the 

 hydrofluoric acid of which we have spoken. 



Thus, without preparing fluorine, without being able to separate it 

 from the substances with which it is united, chemistry has been able to 

 study and to analyze a great number of its compounds. The body was 

 not isolated, and yet its place was marked in our classifications. This 

 well demonstrates the usefulness of a scientific theory, a theory which 

 is regarded as true during a certain time, which correlates facts and 

 leads the mind to new hypotheses, the first causes of experimentation; 

 which, little by little, destroy the theory itself, in order to replace it 

 by another more in harmony with the progress of science. 



Thus certain properties of fluorine were foreseen even before its isola- 

 tion became possible. 



Let us now see what attempts were made not only with hydrofluoric 

 acid, but also with the fluorides to isolate fluorine. 



I have already spoken of Davy's experiments, in which, most notably, 

 he proved that hydrofluoric acid contained no oxygen. In addition to 

 these experiments Davy made many others which I will briefly recall. 



We can in a general way divide the researches upon fluorine into two 

 great classes : 



1. Experiments made by the electrolytic method, either upon the 

 acid or upon fluorides. 



2. Experiments in the dry way. From the beginning of these 

 researches it was foreseen that fluorine, when isolated, would decom- 

 pose water; consequently all the attempts made by the wet way since 

 the first work of Davy had no chance of success. 



Humphrey Davy made many electrical experiments, and these were 

 carried out in apparatus of platinum or of fused (cast) chloride of silver 

 with the powerful voltaic pile of the Royal Society. 



He found that hydrofluoric acid was decomposed, despite the fact that 

 it contained water, and then that the electric current seemed to pass 

 with much more difficulty. He tried also throwing the electric sparks 

 into the acid liquid, and was able in some attempts to obtain by this 

 method a small quantity of gas. But the acid, although cooled, was 

 rapidly dissipated in vapor and the laboratory soon became uninhab- 

 itable. Davy even became quite ill from breathing the vapor of hydro- 



