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396 /, NicJdes on Fluorine. 



and make a tracing of any regular figures : then fill a platinum 

 crucible half full of sulphuric acidj and turn in some water suf- 

 ficient io raise the temperature considerablj, and cover the cru- 

 cible with the glass, keeping the glass cool above by water. 

 Add more water from time to time to the acid, as the tempera- 

 ture declines, until there is no further increase. At this point, 

 the experiment is done; the lines of the tracing on the glass 

 will be corroded distinctly to the naked eye. From such a result 

 the presence of a notable proportion oi fluorine might be in- 

 ferred. But it is easy to prove the conti\ary : for if the acid be 

 neutralized by an alkaline base so as to make a sulphate, and 

 this salt be subjected to the action of an acid capable of displac- 

 ing the fluohydric acid, the tracing is no more visible than it 

 would be if the acid employed had acted itself alone, that is, it 

 is visible only after moistening with the breath. 



In the state of vapor, all acids will act with more or less en- 

 ergy on glass, and cause an etching, — a fact that should not sur- 

 prise us when we consider how easily water will attack glass in 

 po\yder. These effects take place, even when silica is present 

 which again proves that they may contain no fluorine. To ob- 

 tain the best results, it is well to place the crucible in a sand- 

 bath, and to keep the glass quite cool- 

 Two causes of error thus enter into the researches on fluorine, 

 causes which the processes hitherto employed cannot avoid or 

 set aside. The process I use is simple and serves to correct both jj 



assertions and errors. It consists simply in substituting rock 

 crystal for the glass plate, the former resisting all action but that 

 of fluohydric acid, and its sensitiveness to the latter bein^ so 

 great as to evince the presence of 0*000066 milligram of fluorine. 

 Among the errors to be corrected are those of my own, with 

 reference to the presence of fluorine in bile, saliva, and gelatine. 

 In ten grams of saliva I formerly obtained a decided tracing on 

 glass. But wiih. pure acid I now find none with sixty grams, or 

 even ninety. Twenty litres of blood were necessary to obtain 

 an appreciable effect from the fluorine. 



Bat if there is fluorine in the blood, it should be found in 

 alimentary substances. Still, I have not detected it in 200 litres 

 of the waters of the Rhine, or of the 111 (Bas-Rhin), or in those 

 of the Moselle, La Meurthe, La Meuse, La Seine ; nor in 200 

 grams of the shells of oysters or of wood ashes : these sub- 

 stances still contain small quantities, and it is to be detected only 

 by usmg much larger proportions. The most simple and eco- 

 nomical means of discovering the presence of fluorine in waters 

 is by the examination of the incrustations of boilers. These m- 

 crustations represent the product of the evaporation of a very 

 large quantity of water, and they not only, in general, afford 

 fluorine, but many other substances in small proportions. 



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