384 Account of some Experiments 



spar with concentrated sulphuric acid. One part by weight 

 of fused boracic acid, two parls of fluor spar, and about 

 12 of sulphuric acid, appear to be the proportions best 

 adapted for the purpose. This method will require no 

 explanation when it is considered that boracic acid, , as has 

 already been observed, precipilates silex from liquid sub- 

 silicated fluoric acid. If the heat is gentle, not nearly suf- 

 ficient to occasion the ebullition of the sulphuric acid, and 

 the proportions just reconmiended are used, the retort will 

 not be injured, and pure fluohoracic agid gas will be pro- 

 duced in abundance. When the gas ceases to come over, 

 if the heat is raised, more will be evolved, and there will be 

 distilled over at the same time, a viscid iiuid, which is> a 

 compound of sulphuric acid and fluoboracic acid gas. 

 Now the operation should be stopped, if the object is to 

 obtain merely pure fluoboracic gas, a long continuation of 

 the heat producing some silicated fluoric. Before quitting 

 the subject, it should be observed thai the quantity of sul- 

 phuric acid employed is of considerable consequence to the 

 success of the experiment. If too much is used, there is a 

 great loss of gas from the properly which sulphuric acid 

 has of absorbing fluoboracic acid gas ; and if too little is 

 employed, it soon becomes diluted, and loses the power of 

 generating the gas, though it may still decompose the fluor 

 spar. Both extremes, therefore, are to be avoided, and the 

 proportion of acid mentioned above, as far as my expe- 

 rience goes, appears to be the best. 



I have endeavoured to ascertain the specific gravity of 

 fluoboracic gas. 



The flask exhausted weighed 1400*5 grains. 



Filled with common air .... 1400"5 -f 6'2 



Again exhausted 1400"5 



Filled with pure acid gas . . . 1400*5 + 14* 7. 

 Thus it appears that 100 cubic inches of fluoboracic gas 

 are equal to 73*5 grains. 



MiVI. Gay Lussac and Thenard have described the com- 

 pound of this ;;as and water, a fuming fluid, in many re- 

 spects similar to concentrated sulphuric acid. Like this 

 acid, I have observed that it possesses a slight degree of 

 tenacity, so that it has an oily appearance when poured 

 from one vessel to another; and similar in another respect, 

 it possesses the property of charring animal and vegetable 

 substances, and which the French cliemists observed be- 

 longing to the gas itself. I have found that water con- 

 denses more of this than it docs of any other known gas, 

 no less than 700 limes its volume. The experiment was 



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