132 ANNUAL OF SCIENTIFIC DISCOVERY. 



by a variation of density, M. Matteucci obtained these results. In 

 sulphuric acid, if we take as unity its conducting power when the 

 density is 1.192, w r e find that at a density of 1.030 the conducting 

 power is 0.301, and increases till at a density of 1.259 it is 1.000, after 

 which it diminishes till at a density of 1.G07 it is only 0.344. With 

 nitric acid the quantity of hydrogen gas developed at the negative pole 

 is up to a density of 1.076, the same as that with sulphuric acid, and 

 in proportion as the density is increased the quantity of hydrogen 

 diminishes, so that at a density of 1.315 there is no further develop- 

 ment of it. With nitric acid the quantity of oxygen gas developed at 

 the positive pole diminishes as the density of the acid increases. \V ith 

 solutions of nitric acid having a density of 1.076 to 1.1G2, the quantity 

 of oxygen developed at the positive pole is always greater than that 

 in a solution of sulphuric acid. The relation between the oxygen ob- 

 tained in nitric and in sulphuric acid is as 1.2 to 1. It follows from 

 these experiments, that in nitric acid it is the water alone which is de- 

 composed. Nitric acid at a density of 1.315 conducts better than acid 

 of a greater or less density. Nitric acid differs from sulphuric in this 

 respect, that the former at its greatest density of 1.50 conducts better 

 than at 1.10. A solution of nitric acid at a density of 1.076 has ihe 

 same conducting power as sulphuric acid at its maximum, that is, at 

 1.192. With hydrochloric acid the conducting power increases from a 

 density of 1.076 to 1.114, after which it decreases, and at 1.186 it 

 conducts worse than at 1.162. At a density of 1.023 it has a con- 

 ducting power equal to that of sulphuric acid at its maximum. The 

 conducting power of oxalic and phosphoric acid increases with the 

 density of the solutions. Phosphoric acid at 1.115 has the same con- 

 ducting power as sulphuric acid at 1.021. A solution saturated with 

 oxalic acid has about the same power as a very weak solution of sul- 

 phuric acid at a density of 1.022. The author then details some fur- 

 ther experiments, and at the close remarks : "It would, then, be im- 

 possible to conclude from these experiments that the development of 

 electricity in the combination of acids and oxides is subject to the same 

 law as is electricity developed in the oxidation of a metal. The great 

 conducting power of very concentrated nitric acid explains, in part at 

 least, the superiority of this acid over the others in the development 

 of electricity produced by its combination with the oxides." 



VARIATIONS OF THE MAGNETIC FORCES. 



PROF. W. A. NORTON communicates to SiUiman's Journal for No- 

 vember a paper on the diurnal and annual variations of the magnetic 

 needle, in continuation of a former paper on the same subject.* The 

 conclusions derived from both papers are as follows : 1. The diurnal 

 and annual variations of the horizontal magnetic intensity are due to 

 the joint operation of the variations of temperature and of humidity. 

 2. The similar variations in the height of the barometer are attribu- 

 table to the same causes, the variations in both cases following the 



* Sec Animal of RciiMtifir Tli.*rorrry. l Q ~n. p. \:\'>. 



