FLUORINE. 263 



fluoric acid, and lie advised allcbemists to take tlie greatest precautions 

 to avoid its action upon the skin and tlie bronchial tubes. Gay Lussac 

 and Thenard also suffered much from the same acid vapors. 



The other experiments of Davy (I can not cite them all) were chiefly 

 directed to the reaction of chlorine upon fluorides. They presented 

 very great difficulties, for at tliat time the fluohydrates of the fluorides 

 were unknown, nor was it known how to prepare the majority of the 

 anhydrous fluorides. 



These researches of Davy are, as should be expected, of the highest 

 importance, and one remarkable i)roperty of fluorine was put in evi- 

 dence. In those experiments which yielded a small quantity of this 

 radicle of the fluorides the vessels of gold or platinum in which the 

 reaction took place were profoundly attacked. In this case fluorides 

 of gold or of platinum were formed. 



Davy varied in many ways the conditions of his experiments. He 

 repeated the reaction of chlorine upon a metallic fluoride in vessels of 

 sulphur, of carbon, of gold, of platinum, etc.; and he never attained to 

 a satisfactory result. He was thus led to think that fluorine undoubt- 

 edly possessed a chemical activity much greater than that of known 

 substances. 



In closing his memoir, Humphry Davy suggests that these experi- 

 ments might succeed if they were performed in vessels of fluor spar. 

 We shall see that this idea has been taken up by different investigators. 

 To read the work of Davy will interest you, captivate you to the high- 

 est degree. I can best compare this fine memoir with those pictures 

 of the masters to which time only adds new charms. One never tires 

 of admiring them, and discovers in them without end new details and 

 new beauties. 



It was by operating in apparatus made of calcium fluoride that the 

 brothers Knox sought to decompose silver fluoride with chlorine. The 

 chief objection to their experiments is based on the fact that the fluoride 

 of silver employed was not dry. In fact, it is extremely difficult to 

 completely dehydrate the fluorides of silver and mercury. Further- 

 more, we shall see, in the researches of Fremy, that the action of chlorine 

 upon fluorides tends rather to form addition j)roducts — fluochlorides — 

 than to set the fluorine free. 



In 1848, Louyet, also working with apparatus of fluor spar, studied 

 an analogous reaction. He acted with chlorine upon the fluoride of mer- 

 cury. The objections raised against the researches of the brothers Knox 

 also apply to the labors of Louyet. Fremy has shown that fluoride of 

 mercury prepared by Louyet's process contains a notable amount of 

 water. Furthermore, the results obtained were quite variable. The 

 gas collected was a mixture of air, chlorine, and hydrofluoric acid, 

 whose properties varied during the course of preparation. 



The brothers Knox complained much of the action of hydrofluoric 

 acid upon the respiratory passages, and one of them states that after 



