METHODS OF OBTAINING HIDROGEN GAS.

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assumes the form of hidrogen gas. The oxigen is therefore thebond of union between the metal and the acid.

The hissing noise or effervescence observable during the pro-cess is owing to the rapid motion excited in the mixture bymeans of the great number of air-bubbles quickly disengagedand breaking at the surface of the fluid.

Rem ark... We see in this case that two substances exert anattraction, and are even capable of decomposing jointly a third,which neither of them is able to do singly, viz. if we presentsulphuric acid alone, or iron or zinc alone to water, they cannotdetach the oxigen from the hidrogen of that fluid; but if bothare applied, a decomposition is instantly effected. This experi-ment therefore proves that the agency of chemical affinity be-tween two or more bodies may lie dormant, until it is called intoaction by the interposition of another body, which frequentlyexerts no energy upon any of them in a separate state. (SeeChemical Affinity, law V. p. 43 and 52, line 22...28.) In-stances of this kind were formerly called predisposing affinities.

2. Iron in a red heat has also the property of decomposingwater, by dislodging the oxigen from its combination with hi-drogen in the following manner.

Let a gun-barrel having its touch-hole screwed up pass througha furnace or large crucible perforated for that purpose, taking careto incline the barrel at the narrowest part; adjust to its upper ex-tremity a retort charged with water, and let the other extremityterminate in a tube introduced under a receiver in the pneumatictrough. When the apparatus is thus disposed, and well luted,bring the gun-barrel to a red heat, and when thoroughly red-hot,make the water in the retort boil ; the vapour when passingthrough the red-hot tube will yield hidrogen gas abundantly.

Rationale. ..In this experiment the oxigen of the water com-bines with the iron at a red heat, so as to convert it into an oxid,and the caloric applied combines with the hidrogen of the water,and forms hidrogen gas. It is therefore the result of a double

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