M. Arfwedson's Ejcamination of certain Mifierals. 359 



the above statement : but since we are still in want of his ac- 

 countof the manner in which the analysis was performed, it is the 

 more difficult to decide upon, because every method hitherto 

 known of separating boracic acid from its combinations has 

 but incompletely answered its object. From some experi- 

 ments v/hich I have made for the purpose of discovering the 

 composition of boracic acid, by means of its capacity of satura- 

 tion, I have found, that if a boracic salt, borax for instance, be 

 mixed with from three to four times its weight of finely-pow- 

 dered fluor-spar, free from silica, and a sufficient quantity of 

 concentrated sulphuric acid, and the mixture be evaporated to 

 dryness and exposed to a red-heat, that in this manner the 

 entire proportion of boracic acid may be expelled, in the form 

 of fluo-boracic acid. If, after this, the quantity of the base is 

 determined, then the composition of the salt is at the same 

 time obtained*. 



This analytical method is naturally applicable to all boracic 

 salts with fixed bases, which can be decomposed by sulphuric 

 acid ; and as the boracite belongs to this number, I have been 

 enabled to repeat Professor Stromeyer's experiment, in hopes 

 of obtaining a result in some degree worthy of reliance. 



In order to free the boracite from any possible admixture 

 of its matrix, consisting of sulphate of lime, a portion of the 

 finely-powdered mineral was repeatedly washed and levigated 

 with water, after which it was placed on a filter, washed and 

 dried. 



Of this powder 0,849 gram, were mixed in a platinum cru- 

 cible with three grammes of finely-powdered Derbyshire fluor- 

 spar, concentrated sulphuric acid being afterwards poured 

 over it, with due precaution, in order to avoid the spirting up 

 during the evolution of the gas ; then desiccated, and finally 

 ignited. For the sake of obtaining a certain result, the mass 

 was once more treated with sulphuric acid, but the peculiar 

 smell of the fluo-boracic acid could not be perceived this time; 

 which proved that the decomposition had been completed in 

 the first pi'ocess. 



The sulphate of magnesia was afterwards extracted with 

 water, and the undissolved part washed on the filter, until 

 I could be quite certain that nothing of the sulphate of mag- 

 nesia remained amongst the sulphate of lime. The filtered 



• I have found in two experiments made in this manner, that borax, de- 

 prived of its water of crystallization, consists of 



1. 2. 



Boracic acid 68,6 Boracic acid 69,2 



Soda 31,4 Soda .30,8 



100,0 100,0 



and 



