OF VITAL FORCE IN GENERAL. 47 



element to be discovered, we could not know its properties in regard to 

 heat, electricity, or magnetism, the mode of its combination with other 

 elements, the nature and properties of the compounds produced, their 

 reactions with other compounds, &c., until we have tried a complete 

 series of experiments upon it, that is, until we have placed it in all the 

 circumstances or conditions requisite to manifest the properties, with_ 

 which we seek to become acquainted, or whose absence we seek to de- 

 termine if they do not exist. Now we might have made all the experi- 

 ments we could devise upon such a body ; and yet we might have failed 

 in detecting some remarkable and distinguishing property inherent in it, 

 simply because we had not placed it in the requisite circumstances for 

 the manifestation of this peculiarity. Further, even in the elements or 

 compounds with which we are best acquainted, it is very possible that 

 properties exist, of which we as yet know nothing, simply because they 

 have not yet been called into action by the requisite combination of 

 conditions. For example, no one would have thought it possible, a few 

 years since, that water could be frozen in a red-hot metallic vessel; and 

 yet this is now known to be effected with ease and certainty, in the 

 proper combination of conditions. 



57. Again, the properties of a compound substance are, in general at 

 least, altogether different from those which present themselves in either 

 of its components; so that we could not in the least degree judge of the 

 former from the latter, or of the latter from the former. What more 

 different, for example, than the physical and chemical properties of 

 Water, from those of either the Oxygen or the Hydrogen that enter 

 into its composition ? Or what more different than the properties of a 

 neutral salt, from those of the acid and alkali by whose union it is pro- 

 duced ? Further, the properties of a substance may be completely 

 changed, by an alteration in its condition as regards Heat or any other 

 of the forces, already mentioned. For example, the particles of water 

 have so strong an attraction for each other, at a low temperature, as to 

 become aggregated in a crystalline form, and to produce a dense solid 

 mass ; at somewhat a higher temperature, their mutual attraction is so 

 slight, that a very small amount of mechanical force is sufficient to sepa- 

 rate them, and they move upon each other with the utmost freedom ; 

 whilst at a still higher temperature, they manifest a power of mutual 

 repulsion, which increases with the greatest rapidity with every augmen- 

 tation of temperature. Yet when the temperature of the substance is 

 lowered to its former standards, we observe that it first returns to the 

 liquid, and then to the solid form ; and that, in those states, it manifests 

 all the properties which before characterized it. Not merely the phy- 

 sical, but the chemical properties of bodies may be affected by a change 

 in their mechanical condition. Thus, it is well known that oxygen and 

 iron, at ordinary temperatures, have a mutual affinity, which is only 

 sufficient to produce a slow combination between them ; whilst at high 

 temperatures, that affinity is such as to cause their rapid and energetic 

 union. Now if iron, in a state of very minute division, such as it pos- 

 sesses when set free from the state of oxide by means of hydrogen, at the 

 lowest possible temperature, be brought into contact with oxygen or even 

 with atmospheric air, at ordinary temperatures, it immediately becomes 



