500 FLUORIC ACID. 



the subject was forgotten, till Mr. Scheele revived it. The acid of 

 Scheele was, however, impure, and it was not till Gay-Lussac and 

 Thenard obtained it,* that it was known in purity. 



2. ORIGIN AND NAME. Exists abundantly in the beautiful mine- 

 ral called Derbyshire spar ; it being found in great quantities in tha.t 

 county, in England. This mineral is called also fluor, or fluor spar, 

 because, being fusible, it is used as a flux for ores. It is usually 

 crystallized in cubes, with an octahedral nucleus, which gives, by con- 

 tinued dissection, octahedra and tetrahedra. When pure, it is white, 

 but it is most commonly colored. 



Jls the fluor spar affords the acid in question, the name, fluoric 

 acid, was bestowed, because the composition was then, as it is still, un- 

 known. 



3. PREPARATION. 



(a.) Gay-Lussac and Thenard employed a leaden cylinder, con- 

 nected by a recurved leaden tube, with another leaden vessel for a re- 

 ceiver ; the latter was kept cold by ice. 



(b.) Finding lead so liable to fusion, I have used a silver alembic, 

 with a capacity of 16 fluid ounces, its head and tube 2j, and the tube 

 fitted tight to a silver bottle of 3J oz. the latter furnished with a 

 ground silver stopper, to preserve the acid, and to save the necessity 

 of pouring it into another vessel. 



(c.) In the alembic are placed 2 oz. of pure fluor spar, and 4 oz. 

 of strong sulphuric acid ; the receiver is surrounded by ice or snow, 

 and a few live coals are placed beneath the alembic, whose head is 

 made securely tight by a lute of finely powdered pipe clay, placed in 

 the joint, and a rag, smeared with the same, is bound tightly over it. 

 The receiver should not be pressed hard home, so as to be accurate- 

 ly tight upon the tube, but a little room should be left for the escape 

 of the vapor of the acid. 



(d.) The apparatus should be under a well drawing flue, the hands 

 protected by thick gloves, and the receiver, when moved, should be 

 grasped by small tongs, furnished with curvatures, to fit the neck of 

 the bottle. f In about half an hour, the process will be through, and 



* Recher. Phy.-Chim. Vol. II. 



t As represented in the annexed figures, which being made with corresponding 



c==o =-~ 



flexions, and of various sizes, from those that are very delicate and adapted to sustain 

 the minutest flasks by the neck, to such as will lift a heavy crucible, or a basin, are 

 highly convenient. 



