120 DR. FARADAY'S EXPERIMENTAL RESEARCHES IN ELECTRICITV. 



grains. They were about five inches long, and 0*4 of an inch wide. An earthenware 

 pneumatic trough was filled with dilute sulphuric acid, of the strength just described 

 (863.), and a gas jar, also filled with the acid, inverted in it*=. A plate of platina of 

 nearly the same length, but about three times as wide as the zinc plates, was put up 

 into this jar. The zinc plate A was also introduced into the jar, and brought in con- 

 tact with the platina, and at the same moment the plate B was put into the acid of 

 the trough, but out of contact with other metallic matter. 



865. Strong action immediately occurred in the jar upon the contact of the zinc 

 and platina plates. Hydrogen gas rose from the platina, and was collected in the 

 jar, but no hydrogen or other gas rose from either zinc plate. In about ten or twelve 

 minutes, sufficient hydrogen having been collected, the experiment was stopped ; 

 during its progress a few small bubbles had appeared upon plate B, but none upon 

 plate A. The plates were washed in distilled water, dried, and reweighed. Plate B 

 weighed 148*3 grains, as before, having lost nothing by the direct chemical action of 

 the acid. Plate A weighed 154*65 grains, 8*45 grains of it having been oxidized 

 and dissolved during the experiment. 



SQQ. The hydrogen gas was next transferred to a water-trough and measured ; it 

 amounted to 12*5 cubic inches, the temperature being 52°, and the barometer 29*2 

 inches. This quantity, corrected for temperature, pressure, and moisture, becomes 

 12*15453 cubic inches of dry hydrogen at mean temperature and pressure ; which, in- 

 creased by one half for the oxygen that must have gone to the anode, i.e. to the zinc, 

 gives 18*232 cubic inches as the quantity of oxygen and hydrogen evolved from the 

 water decomposed by the electric current. According to the estimate of the weight 

 of the mixed gas before adopted (791.), this volume is equal to 2*3535544 grains, 

 which therefore is the weight of water decomposed ; and this quantity is to 8*45, the 

 quantity of zinc oxidized, as 9 is to 32*31. Now taking 9 as the equivalent number 

 of water, the number 32*5 is given as the equivalent number of zinc ; a coincidence 

 sufficiently near to show, what indeed could not but happen, that for an equivalent 

 of zinc oxidized an equivalent of water must be decomposed -{-. 



867. But let us observe how the water is decomposed. It is electrolyzed, i. e. is 

 decomposed voltaically, and not in the ordinary manner (as to appearance) of chemical 

 decompositions ; for the oxygen appears at the anode and the hydrogen at the cathode 

 of the decomposing body, and these were in many parts of the experiment above an 

 inch asunder. Again, the ordinary chemical affinity was not enough under the cir- 

 cumstances to effect the decomposition of the water, as was abundantly proved by 

 the inaction on plate B ; the voltaic current was essential. And to prevent any idea 

 that the chemical affinity was almost sufficient to decompose the water, and that a 

 smaller current of electricity might, under the circumstances, cause the hydrogen to 



* The acid was left during a night with a small piece of unamalgamated zinc in it, for the purpose of evolving 

 such air as might be inclined to separate, and bringing the whole into a constant state, 

 t The experiment was repeated several times with the same results. 



I 



