496 Mr. J. Denham Smith on the 



stances should greatly vary, electric currents generated by 

 given elements might be rendered available on various occa- 

 sions; — to ascertain, for instance, the connection of saline 

 springs not very distant from each other, often appearing at 

 the surface or in mines; or of a metalliferous vein discovered 

 in one place, with a vein which has been worked for ore in 

 another. The conducting power of the circuit at Pennance 

 mine, already described, was in this way found to equal that 

 of a tolerably strong solution of common salt, the current in 

 the latter experiment having to traverse an inch of the solu- 

 tion and short copper wires to complete the circuit. The 

 conducting power of the rocks or strata in this case, there- 

 fore, appeared to be very great. 



When some sulphate of copper was added to the solution, 

 the conducting power of the latter exceeded that of the strata. 

 Glass tubes filled with solution of salts in different known 

 proportions might be used as tests in experiments on the re- 

 lative conducting power of different strata, and they might be 

 referred to as standards in describing the results. 



LXI. On the Constitution of the Subsalts of Copper. — No. I. 

 On the Subsulphates. By J. Denham Smith, Esq.* 



r | 1 HE results of several analyses of some of the basic salts 

 ■* of copper made at a former period not agreeing with the 

 constitution ascribed in many instances to these compounds, 

 again directed my attention to their composition, and further 

 experience has confirmed this disagreement, showing either 

 that the anal v tic results are in one case incorrect, or that the 

 composition of these salts, prepared at various times by the 

 same method, is not constant. 



The mode adopted for determining the composition of the 

 subsulphates of copper, was to dissolve one portion of the salt 

 in pure hydrochloric acid, and ascertain the quantity of sul- 

 phuric acid by a salt of barytes. To estimate the proportion of 

 black oxide of copper, the course pursued in the experiments 

 alluded to, was solution of another portion of the salt, under 

 examination, in dilute sulphuric acid and precipitation by a 

 caustic alkali from the boiling solution, carefully washing, ig- 

 niting, and weighing the precipitate. This mode, however, is 

 open to the objection of the possible adherence of portions of 

 the precipitant, or other foreign matter, to the oxide ; and as 

 I subsequently found that this class of salts when exposed to 

 a lengthened and bright ignition, care being taken not to fuse 

 the oxide, loses the whole of its sulphuric acid, I adopted 



* Communicated by the Chemical Society; having been read April 4, 

 1843. 



