1824.] M. Benelius on Fluoric Acid. 339 



only one which I succeeded in freeing completely from the 

 last portions of silica. 



100 parts of the fluate of lime thus prepared and purified were 

 digested in the state of an impalpable powder in concentrated 

 sulphuric acid, and after a considerable interval, the mixture was 

 evaporated to dryness and ignited. In different experiments, I 

 obtained 174*9, 175, and 175-12 parts of sulphate of lime. Of 

 these numbers, I consider the middle one, 175, to be the most 

 accurate. According to this experiment, fluate of lime is com- 

 posed of 



Fluoric acid 27-3225 100 



Lime 72*6775 266 



And the atomic weight of fluoric acid is 270-34, instead of 275, 

 the number which 1 had previously given in my tables. It may, 

 perhaps, be objected that the number 270*34 is not an equimul- 

 tiple of 6-25, which has been considered as the true atomic 

 weight of hydrogen, and which many philosophers are of opi- 

 nion ought to divide without a remainder the atomic weights of 

 all other substances. I do not think that any argument of 

 general application can be deduced from the circumstance that 

 the atomic weight of oxygen is divisible without a remainder by 

 this number, and that the atomic weights of several other sub- 

 stances approach very nearly to equimultiples of 6-25.* This 

 number is so small, when compared with the atomic weights of 

 most other substances, that it is generally exceeded by the un- 

 avoidable errors of experiment ; consequently, more decisive 

 proofs than any hitherto obtained are required from this source, 

 before the question can be finally answered. We are as yet 

 acquainted with no physical circumstances which render this 

 simplicity of relation a necessary law of nature, and until this be 

 proved, we must continue to regard the supposed system of mul- 

 tiples as very possibly nothing else than a seducing hypothesis- 

 Be that as it may, the former atomic weight of fluoric acid, 275, 

 which is an equimultiple by 44 of 6-25, is unquestionably too 

 high. Those chemists who will be disposed to correct the new 

 atomic weight in conformity with tlie supposition alluded to 

 above, will make it 268*75, a number which certainly differs very 

 little from 270*34, but is in so far arbitrary, that it does not 

 result from any direct experiment. 



Double Salts of Fluoric Acid with two Saline Bases.— The acid 

 filiates of the alkaline bases possess a remarkable tendency to 

 combine with a different base, in the proportion requisite to 



• From the experiments which I made in company with M. Dulong on the composi- 

 tion of water and on the specific gravity of hydrogen gas, it follows that the atomic 

 weight of hydrogen is 6-2177. This numher I have adopted in my tables, and it is 

 obvious that a very inconsiderable deficiency in the number 6-25 would overthrow the 

 whole hypothesis. 



7,2 



