FLU 



FLU 



I 



tended the lectures of this professor, and 

 think, in one of them, he said he had de- 

 composed the fluoric acid : for want, 

 however, of any written document on the 

 subject, we must content ourselves with 

 a summary account of the properties of 

 this acid, which were investigated with 

 accuracy and precision by Scheele and 

 Priestley. The spar was not distinguish- 

 ed from others of a similar appearance till 

 about the year 1768, when Margraff at- 

 tempted to decompose it by means of the 

 sulphuric acid. He found that it consisted 

 of a white sublimate, and a peculiar acid; 

 the sublimate proved afterwards to be 

 lime, and the acid being denominated 

 fluoric acid, it is now called the fluate of 

 lime. Margraff found, to his astonish- 

 ment, that the glass retort in which the 

 experiment had been made was corrod- 

 ed, and even pierced with holes. 



Fluoric acid may be obtained by put- 

 ting a quantity of the spar in powder into 

 a retort, pouring over it an equal quan- 

 tity of sulphuric acid, and then applying 

 a gentle heat. A gas ensues, which may 

 be received in the usual manner, in jars, 

 standing over mercury. This gas is the 

 fluoric acid, which may be obtained dis- 

 solved in water, by luting to the retort a 

 receiver containing that fluid. The dis- 

 tillation is to be conducted with a very 

 moderate heat, to allow the gas to con- 

 dense, and to prevent the fluor itself from 

 subliming. 



Soon after the discovery of this acid, it 

 was doubted whether it possessed those 

 properties that rendered it different from 

 all other acids. Scheele, however, who 

 had already investigated the subject, in- 

 stituted another set of experiments, which 

 completely established the fact. 



The properties of this acid are, that, 

 as a gas, it is invisible, and elastic like 

 air : but it will not maintain combustion, 

 nor can animals breathe it without death. 

 In smell it is pungent, something similar 

 to muriatic acid. It is heavier than com- 

 mon air, and corrodes the skin. When 

 water is admitted in contact with this 

 gas, it absorbs it rapidly ; and if the gas 

 be obtained by means of glass vessels, it 

 deposits at the same time a quantity of 

 silica. Water absorbs a large portion of 

 this gas, and in that state it is usually 

 called fluoric acid by chemists. It is then 

 heavier than water, has an acid taste, 

 reddens vegetable blues, and has the 

 property of not congealing till cooled 

 down to 23. The pure acid may be ob- 

 tained again from the compound by 



means of heat. Fluoric acid gas does not 

 act upon any of the metals ; but liquid 

 fluoric acid is capable of oxyding iron, 

 zinc, copper, and arsenic. It does not 

 act upon the precious metals, nor upon 

 platina, mercury, lead, tin, antimony, 

 cobalt. It combines with alkalies, earths, 

 and metallic oxides, and, with them, 

 forms salts denominated fluates, of which 

 the true fluor, Derbyshire spar, or fluate 

 of lime, consists of 



Lime 57 



Fluoric acid - ... 16 

 Water 27 



100 



The most remarkable property is that 

 already alluded to, viz. the facility with 

 which it corrodes glass and siliceous bo- 

 dies, especially when hot, and the ease 

 with which it holds silica in solution, even 

 when in a state of gas. This affinity for 

 silica is so great, that the thickest glass 

 vessels can withstand its action only a 

 short time. The order of its affinities is, 



Alumina 

 Ammonia 



Barytes 



Lime 



Magnesia 



Potash 

 Silex 

 Soda 

 Strontian. 



As fluoric acid produces an insoluble 

 compound with lime, it may be employed 

 to detect the presence of that earth when 

 held in solution. Two or three drops only 

 of the acid will cause a milky cloud or pre- 

 cipitate to appear, if any lime is present. 



Fluoric acid has been applied to engra- 

 ving or etching on glass, and was used, ac- 

 cording to Beckman, nearly a century and 

 a half ago for that purpose, by an artist at 

 Nuremberg, who obtained it from digest- 

 ing fluor spar in nitric acid. Since, how- 

 ever, the discoveries of Scheele and 

 Priestley,it has been more generally used, 

 and the art is performed by covering the 

 glass with wax, and then that part where 

 the figures are to appear is laid bare, and 

 the whole is exposed for some time to the 

 hot vapour of fluoric acid. This simple 

 process is employed with great advantage 

 in writing labels on glass vessels, and in 

 graduating thermometers, &c. See Thom- 

 son's Chemistry. 



FLUSTKA, in natural history, horn- 

 wrack, a genus of worms, of the order 

 Zoophyta. Animal a polype, proceeding" 

 from porous cells ; stem fixed, foliaceous, 

 membranaceous, consisting of numerous 



