STUDIES ON THE PHENOMENA OF CONTACT. 405 



peai-, at the end of a certain time, if the platiiia Avire ascends to the top of the 

 tube. At the same time that the hydrogen disappears metallic gold is precip- 

 itated on the portion of the platina wire Avhich is immersed in the metallic 

 solution. In this experiment the hydrogen is burned by the chloride of gold, 

 instead of being burned by the oxygen, as in the previous experiment. The 

 positive electricity of the platina unites with the negative electricity of the 

 hydrogen, and the negative fluid of the platina unites with the positive elec- 

 tricity of the salt. When the hydrogen reduces the latter, there are formed 

 chloiliydric acid and metallic gold. The same thing would take place if we 

 operated witlwut the j)Jatina, but at a high temperature only, as has been already 

 observed in reference to hydrogen and oxygen alone; for heat, as well as the 

 presence of a third body, develops polarity. 



We have here exactly the phenomena Avliich are 2)resented by the voltaic pile ; 

 in fact, a jiile is composed of two different metals and of a liquid which can act 

 on one of the metals. If we take water as the liquid, pure ii-on and pure copper 

 as the metals, and plunge the pure iron alone in the water, there is no action ; 

 but if we add a third body — the copper — action exhibits itself, as the galvanometer 

 indicates, the iron is oxidized, and hydrogen is disengaged. Volta intro- 

 duced, from the beginning, three substances into the composition of his pile — 

 two metals and moistened cloth. 



The following are additional experiments: Take a porous vessel and place it 

 in a glass. In the porous vessel put hydrochloric acid ; in the glass, nitric 

 acid ; then let a strip of gold be placed in each receptacle ; so long as 

 the two strips remain separated there is no action ; but, on bringing them 

 together, they are immediately attacked, and the gold in the hydrochloric acid 

 is dissolved; the nitric acid is at the same time deoxidized by the nascent 

 hydrogen conveyed through the sides of the porous vase, while an electric 

 current traverses the strips of gold. 



I'urthcr, hydrochloric acid mixed with nitric acid does not act on tlu; latter if 

 the two acids are diluted; but if we add a third body, iron, copper, gold, 

 plaLina, &c., action commences instantly ; the chlorine is disengaged, the nitric 

 acid is deoxidized, and the metal combines with the chlorine. 



It is known that zinc oxidizes slowly in water, because it is an electro-pos- 

 itive metal ;. the disengagement of hydrogen in this case is very slow at the 

 ordinary temperature — so slow as scarcely to be perceptible. But if a highly 

 electro-negative body, such as sulphuric acid, be added, the polarity of the 

 zinc is augmented ; it becomes so electro-positive that the hydrogen is driven 

 with violence from its combination, and the zinc becomes its substitute. Before 

 the addition of the acid the polarity of the zinc was analogous to that of the 

 hydrogen ; but after that addition the metal becomes much more electro-posi- 

 tive than the hydrogen. Here is a phenomenon of polarity identical with 

 that which takes place when a strip of platina is introduced into a deto- 

 nating mixture. The sulphuric acid here acts, in regard to the zinc, as the 

 platina towards the hydrogen. 



I shall here cursorily cite some circumstances in which the influence of the 

 presence of a third body makes itself felt in the most ordinary cases : 



1. Pure iron in dry air is not attacked ; in humid air it oxidizes. 



2. Iron, in boiled water, (not aerated,) does not oxidize ; in aerated water, 

 oxidizes. 



3. The peroxide of manganese (MNO^) calcined in oxygen (or in air) does 

 not alter;* heated in presence of oxygen and a base, a manganate is formed, 

 (RO, MNOl) 



4. When electric sparks arc passed into a mixture of dnj nitrogen and 

 oxygen, no reaction is observed ; if the two gases are moistened, nitric acid is 

 formed. 



If the temperature is very high, it loses oxygeu. 



