STUDIES ON THE PHENOMENA OF CONTACT. 409 



this last being better understood, will bo siisceptibb; of tlic same explanation 

 as clLcmical reactions in general. 



It remains to examine the eftects produced by the oxygenated water of 

 Thenard, and which arc usually regarded as catalytic phenomena. 



Oxygenated water is one of the most electro-negative bodies known ; hence 

 it acts in all cases as an oxidizing and energetic aci'd. When placed in con- 

 tact with the powder of platina a lively effervescence is observed, tlu; pLatina 

 is not altered, all the oxygen of the oxygenated water is disengaged, and we 

 obtain water, pure oxygen, and pure metal. This reaction is precisely what 

 was to be expected : in effect the oxygenated water acts towards the platina 

 as an acid ; it tends to oxidize the metal, that is to say, in this phonomenon 

 the platina is electro-positive, the oxygenated water electro-negative. The 

 platina tends to form a peroxide, but this oxide not being susceptible of being 

 formed under these circumstances, the phenomenon of polarity takes place 

 nevertheless, and the oxygen is disengaged. 



Th(; same thing occurs if we treat comminuted platina witli nitric acid. This 

 acid, which is an energetic oxidant, like oxygenated 'water, is decomposed 

 at a temperature much lower than if the platina were not present. I have 

 observed lately that this phenomenon takes place witli certain sulphurcts, es- 

 pecially with certain specimens of sulphuret of copper from the environs of 

 Lake 15aikal, in Siberia, which were sent to me for analysis. If we take 

 this sulphuret of copper, calcined and dry, and in a state of great division pour 

 upon it concentrated nitric acid, and then heat with an alcoliol lamp, the 

 nitric acid is decomposed, and gives forth ruddy vapors, Avithout attacking the 

 sulphuret, and at a temperature much inferior to that at which nitric acid is 

 decomposed by heat alone. If we would transform the sulphuret into a sulphate 

 we must not operate in this manner, as we lose the acid without obtaining the 

 desired effect. In order to oxidize the sulphuret we must ad4 the acid drop 

 by drop whilst we are applying heat; the sulphuret is then actively attacked. 

 Molybdenum, treated with oxygenated wat(u-, passes, on the contrary, to the 

 acid state, as is the case also with arsenic, selenium, &:c., while silver, gold, 

 mercury, palladium, rhodium, &c., &c., act in these circumstances like platina. 

 In this action of platina and of metals in general, on oxygenated water, an 

 extreme tenuity in the metal is an indispensable condition for obtaining a 

 prompt reaction. This has been equally indicated in speaking of the action of 

 divided platina, and it is the same in every chemical reaction, whatever it 

 may be. 



The oxides which can be oxidized, (Ca', B«', Ca', ike.,) decompose 

 oxygenated water in passing to the state of peroxides, (Ca, Bd, Cd, &c.) The 

 oxides which cannot be oxidized may sometimes effect the decomposition 

 of oxygenated water, because they are highly electro-positive in regard to it, 

 and the phenomenon of polarity takes place. The peroxide of manganese, for 

 example, caunot be oxidized, except in contact with a base with which 

 the manganic acid produced may combine. When this peroxide is added to 

 oxygenated water, manganic acid cannot be formed ; but oxygenated water, 

 being a body but slightly stable and highly electro-negative in regard to M«, 

 reacts on this peroxide and tends to oxidize it. The peroxide of manganese is 

 then in the same situation with platina, silver, dec, cited above. 



The presence of a third body in phenomena of contact does not act solely 

 by exciting a phenomenon of polarity, which, without the presence of the third 

 body, would not occur, unless brought about by a high temperature. It often 

 exercisQS, besides, a very marked inlluence on the products of the reaction, 

 especially if we operate on organic bodies; thus: Take two small tubular 

 retorts of the same; capacity, and jjlacc in the one tartaric acid, in the other 

 tartaric acid and platina sponge ; then let the two retorts be heated at the 

 same temperature, which is easily done by placing both in the same sand-bath. 



