502 FLUO-SILICIC ACID. 



(A.) Respiration. The vapor is extremely dangerous in the 

 lungs ; and should be anxiously avoided. 



(i.) Contact with the body. This also is dangerous ; excepting 

 prussic acid, there is perhaps no agent so deleterious. It instantly 

 disorganises the skin ; painful and obstinate ulcers are formed, for 

 it seems to penetrate into the very tissue of the parts ; there is a 

 general irritation of the system, and sometimes extirpation of the in- 

 jured portion is the only remedy. Even contact with the vapors 

 floating about should be avoided, for they immediately irritate the 

 skin, and may produce permanent injury. J 



(j.) Fluoric acid, largely diluted in vessels of lead, platinum or 

 silver, has a decidedly acid taste, and reddens the vegetable blues. 



(&.) It forms salts with the salifiable bases ; " and with acids weak- 

 er than itself, it produces compounds, in which the latter serve as a 

 kind of base." By dilution with water, these acids suffer a partial 

 decomposition, and deposit a portion of their base ; of this description 

 are fluo-boric, and fluo-silicic acids, which will be described in then 

 places. 



(/.) The constitution and combining weight of fluoric acid will be 

 mentioned at the conclusion of the whole subject. 



FLUO-SILICIC ACID GAS. 



The action of fluoric acid upon silica is so peculiar, as to merit a 

 distinct consideration. 



The strong acid ofGay-Lussac instantly soils glass ; attacking it with 

 as much energy as sulphuric acid does an alkali ; heat is evolved, and 

 instead of having its volatility diminished, it becomes, by this union, 

 permanently aeriform ; a true gas ; although before only a vapor. 



1. PREPARATION. 



(a.) This gas is of course produced, whenever the ordinary process 

 for fluoric acid is performed in glass vessels, but it is usual to add half 

 as much pulverized glass asfluor spar to the mixture of equal parts of 

 the latter, and strong sulphuric acid. 



(b.) In the latter case, the glass retort will be much less corroded, 

 but in my experiments it has always been attacked in some degree, , 



I Gay-Lussac and Thenard mention (Recher.-Phys. Chim. Tom. II, p. 11,) that 

 some of their assistants suffered severely for a month, from exposure for a few min- 

 utes to the acid vapor, coming in contact with the fore finger and thumb ; and a dog 

 upon whose back, deprived of hair at that place, six drops of this acid were allowed 

 to fall, suffered extremely, and in a few hours died in agony. They state that the 

 effect is not always perceived till 7 or 8 hours after the contact of the vapor, and 

 that even when it is too feeble to be observed, it produces in a few hours, acute 

 pain, loss of sleep, and fever. Similar results have several times been observed in 

 my laboratory. 



