FLUO-BORIC ACID. 505 



(d.) Diamonds and various gems have been exposed to the action 

 of fluoric acid, but without much effect.* 



FLUO-BORIC ACID GAS. 



1. HISTORY. This singular compound was obtained about the 

 same time by Gay-Lussac and Thenard and by Sir H. Davy, although 

 the former gentlemen first published their observations. Both had 

 the same object in view, that of obtaining fluoric acid gas free from 

 water. 



2. PROCESS. 



(a.) A coated iron tube; vitreous boracic acid 1 part and fluor 

 spar 2, with heat. 



(6.) An easier way is to distil, in a glass retort, 1 part vitreous 

 boracic acid, 2 fluor spar and 12 strong sulphuric acid.\ Common 

 crystallized boracic acid answers perfectly well.f 



3. PROPERTIES. 



(a.) Colorless and transparent, and, over mercury, permanently 

 aeriform. It reddens litmus. 



(b.) Sp. gr. 2.36; at 60 Fahr. and 30 in. bar. 100 cubic inches 

 of this gas weigh 72.044 grains. 



(c.) Extinguishes flame and life; very pungent and suffocating, 

 but less so than fluo-silicic acid gas. 



(d.) The bubbles of this gas break, in a moist air, in dense white 

 fumes almost like snow. 



(e.) This arises from the strong attraction of the gas for water, 

 which it detects in almost every other gas and precipitates in a cloud, 

 to the density of which the boracic acid, as well as the moisture, 

 probably contributes. 



(f.) Water absorbs 700 volumes of this gas and acquires the sp. 

 gr. 1.77; although it increases in volume. The acid thus formed is 

 dense, fuming and highly corrosive, and considerably resembles sul- 



* Other stones were also tried. The agate lost its transparency and color ; the 

 avanturine its brilliant particles, and appeared like a gray pebble ; the bloodstone 

 became soft and brittle, and its beautiful colors were changed and became dull ; 

 garnets were corroded, and assumed a dark red color, and the gypsum of Mont- 

 martre and the sandstone of Fontainbleau were dissolved. Rock crystal is not at- 

 tacked so readily as glass, owing to its stronger aggregation. (Gray's Op. Chem. p. 

 457.) The minerals generally lost weight, and the effects may be referred either to 

 the affinity of the fluoric acid for silica or for the other constituents of the stones. 

 Fluoric acid is useful in giving indelible labels upon glass for the laboratory ; and 

 attempts have been made, on the score of economy, to substitute glass plates, cor- 

 roded by fluoric acid, instead of copper plates, and a funeral piece in honor of Scheele 

 was executed in that way; but it is difficult to sustain the glass and prevent it from 

 cracking in the press. 



t J. Davy, Phil. Trans. 1812. 



t The previous vitrification adds considerably to the trouble of the experiment, 

 nd for a class experiment presents no important advantage. 



Thomson, First Prin. Vol. II, p. 179. 



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