Voltaic Batteries^ Sfc. 73 



maintained as nearly as possible the same during the per- 

 formance of any one set of experiments. 



63. These regulations sufficiently provide against every 

 contingency that can affect the correctness of the experiments, 

 except those of the gradually diminishing activity of the acid 

 mixture through continued use, and the accelerated action 

 upon the zinc which occurs during its continued immersion. 



64. Against the effects of these last, especial provision is 

 made as follows : I prepare ten or a dozen of the kind of zinc 

 plates which are the subject of present experiment, and bring 

 each of those by previous management to yield the same 

 amount of action in a given time. This is accomplished by 

 taking one of them as a standard, and by polishing or roughen- 

 m(r as may be needed the surfaces of the others, thus bringing 

 each into precisely the same condition ; and a little practice 

 makes this to be done with considerable facility. 



65. After any one of such a set has been used twice or thrice, 

 its place is supplied with a fresh plate ; and after the whole 

 number may have been so employed, the set is repolished and 

 re-adjusted before their application to any new set of experi- 

 ments. The extreme nicety which this plan introduces into 

 experiments of this kind will be obvious if it be considered 

 that each plate is employed to produce but at most five-tenths 

 of a cubic inch of hydrogen before it is renewed, and conse- 

 auently will have expended in that effort but little more than 

 three-tenths of a grain of its entire weight; a quantity much 

 too small to affect the action of the plate in any way likely 

 to interfere with that degree of nicety which these experi- 

 ments require. And with respect to the effect which so small 

 a quantity of zinc will have upon the acid mixture, either by 

 abstracting its active acid, or by impregnating it with the dis- 

 solved sulphate, if it be considered that the quantity of acid 

 mixture here employed is seldom less than eight or ten gal- 

 lons, and that this too is frequently renewed, it will be obvious 

 that the dissolving in it of even many such minute quantities 

 of zinc will have no effect whatever upon the results of expe- 

 riment. 



66. It will subsequently be seerrhow essential it is that each 

 and all of the above particulars should be strictly attended 

 to ; and preparations being thus made and observed through- 

 out, I know of no other circumstances that can affect the ex- 

 periments or interfere with their accurate performance; and 

 the whole thus arranged admit of being performed with con- 

 siderable ease and expedition. 



67. It has been thought better to place all these particulars 

 under one view, at an early stage of this paper, as well to 



