Chemical Science. 389 



In examining the influential circumstances of this action, two ap- 

 peared to have predominating power ; the degree of dilution of 

 the acid, and the state of the metal. These were estimated by the 

 quantity of gas evolved from given surfaces of zinc in a given time ; 

 and a convenient little apparatus for that purpose was used, which 

 allowed of the quick repetition of the experiments, and furnished 

 accurate results as to the volumes of gas produced. 



Six mixtures of acid and water were used. In the following table, 

 the first column gives the number by which any mixture is distin- 

 guished in the future experiments, the second expresses the specific 

 gravity, and the third the quantity of sulphuric acid per cent 



1 . . 1.137 . . 20.20 



2 . . 1.182 . . 25-64 



3 . . 1.215 . . 29.85 



4 . . 1.258 . . 35.28 



5 . . 1.326 . . 43.25 



6 . . 1.532 . . 64.20 



When the different kinds of zinc were immersed in these acids, it 

 was with the exposure of certain measured and equal surfaces : thus, 

 in the following table, pieces of zinc, each having 200 square mille- 

 metres of surface, were left in the respective acid, until each had 

 evolved 300 cubic millemetres of hydrogen gas ; and the time occu- 

 pied, which constitutes the table, of course expresses inversely the 

 facility with which the acid and zinc evolved gas. 



Acid .... No. 1. No. 2. No. 3. No. 4. No. 5. No. 6. 

 Zinc of commerce 0'.6" 0'.3" 0'.2" 0'.3" 0'.4" 0/9" 

 Distilled zinc . 3'.30" 1'.50" 0'.30" 0'.26" 0'.24" 1/30" 



These experiments were all made with liquid at the same tempera- 

 ture L e., between 10 and 12 C., but the temperature rose, and 

 the more the stronger the action ; thus, with the acid No. 3 it rose 

 about 5 C., or 9 E, in 15 minutes. Another fact to be noticed is, 

 that the action was very slow in all at first, but afterwards rose slowly 

 with the pure zinc, but rapidly with that of commerce : the latter 

 generally attained its maximum action in 10 minutes, the former 

 required several hours for that effect. It appears, also, that the acid 

 No. 3 is that which acts most energetically upon ordinary zinc ; the 

 Nos. 2, 4, and 5 differ somewhat from it; Nos. 1 and 6 much. No. 

 3 contains 30 per cent, of sulphuric acid ; and it may be said gene- 

 rally that, for the evolution of hydrogen most rapidly from ordinary 

 zinc, the diluted acid should contain not less than 25, nor more than 

 50 per cent, of oil of vitriol. 



The action of the acids on pure zinc, it may be observed, does not 

 follow the same order as on ordinary zinc. 



With regard to the cause of the difference between pure and ordi- 

 nary zinc, it might at first be supposed to be due to a degree of open- 

 ness or porosity in the latter, but it was found that each had the same 



