164! M. Henrici o?i the Theory and Application of Electricity. 



Minerals. 



Sodalite, Vesuvius. 



Variety of ht/perst/iene, occurring in 



the diorite on the Lahn, Nassau. 

 Lepidolite, locality unknown. 



Obs'idimi, from Li pari. 

 MicUy Spessart, Bavaria. 



Granite, Odenwald, Germany. 



Chlorite slate, locality unknown. 



Augite porphyry y locality unknown. 

 Mica slate, locality unknown. 

 Gneiss, Odenwald, Germany. 

 Two specimens of Scotch granite, 



localities unknown, 

 Tincal, or native borax, from East 



Indies. 



Phosphoric acid. 



Trace; had not enough for a second 

 analysis. 

 Distinct traces. 



I obtained so large a precipitate, that 

 I think it must form an important 

 constituent of this mineral. 



Present in considerable quantity. 



Minute traces, but more abundant in 

 another specimen from Russia. 



Enough to give all the usual tests 

 from about 1^ ounce. 



Sufficient from two ounces to give a 

 precipitate with nitrate of silver. 



Considerable traces. 



Enough for nitrate of silver test. 



Considerable traces from two ounces. 



Large precipitate from two ounces. 



The quantity of phosphoric acid in 

 this substance was very considerable, 

 being equal in one instance to 2-13 

 per cent. I think most native borax 

 will be found to contain phosphate 

 of soda. 

 Dntholite. In one specimen of this mineral from 



Andreasberg in the Harz, the quan- 

 tity of this acid present was suffi- 

 ciently large to be estimated. I also 

 detected its presence in a specimen 

 from North America, but in neither 

 case had I enough of the mineral to 

 make another analysis. 



It is very curious that such a large quantity of phosphoric 

 acid should in these two cases be associated with boracic acid, 

 which is of a decided volcanic origin. It would be verv in- 

 teresting if the substances occurring with the native boracic 

 acid in Tuscany, and also the other minerals containing boracic 

 acid, were examined for phosphoric acid. The quantitative 

 determination of the phosphoric acid in rocks would, in mv 

 opinion, be of little importance, as phosphoric acid, although a 

 constant, is a very variable constituent. This, however, does 

 not apply to the simple minerals, such as olivine, of which it 

 forms very probably a constant constituent. 

 Dublin, July 17, 1845. 



XXVI. Some Observatiotis on the Theory and Application of 



Electricity. By F. C. Henrici*. 

 1. TT is usually considered, that in consequence of the sup- 

 J- posed repulsion exerted between the particles of elec- 

 * From PoggendorfTs Annalen, vol. Ixiv. p. 345. 



