FAMILIAR LETTERS ON CHEMISTRY. 



pounds weight. In the same manner, six pounds weight of coal are equivalent to 

 thirty-two pounds weight of zinc. The numbers representing chemical equivalents 

 express very general ratios of effects, comprehending for all bodies all the actions 

 they are capable of producing. 



If zinc be combined in a certain manner with another metal, and submitted to 

 the action of dilute sulphuric acid, it is dissolved in the form of an oxide ; it is 

 in fact burned at the expense of the oxygen contained in fluid. A consequence 

 of this action is the production of an electric current, which, if conducted through 

 a wire, renders it magnetic. In time affecting the solution of a pound weight, for 

 example, of zinc, we obtain a definite amount of force adequate to raise a given 

 weight one inch, and to keep it suspended ; and the amount of weight it will be 

 capable of suspending will be the greater the more rapidly the zinc is dissolved. 



By alternately interrupting and renewing the contact of the zinc with the acid, 

 and by very simple mechanical arrangements, we can give to the iron an upward 

 and downward or a horizontal motion, thus producing the conditions essential to 

 the motion of any machinery. 



The moving force is produced by the oxidation of the zinc ; and, setting aside 

 the name given to the force in this case, we know that it can be produced in another 

 manner. If we burn the zinc under the boiler of a steam engine, consequently in the 

 oxygen of the air, instead of the galvanic pile, we should produce steam, and by 

 it a certain amount of force. If we should assume (which, however, is not proved), 

 that the quantity of force is unequal in these cases that, for instance, we had 

 obtained double or triple the amount in the galvanic pile, or that in this mode of 

 generating force less loss is sustained we must still recollect the equivalents of 

 zinc and coal, and make these elements of our calculation. According to the 

 experiments of Despretz, six pounds weight of zinc, in combining with oxygen, 

 develope no more heat than one pound of coal ; consequently, under equal condi- 

 tions, we can produce six times the amount of force with a pound of coal as with a 

 pound of zinc. It is therefore obvious that it would be more advantageous to 

 employ coal instead of zinc, even if the latter produced four times as much force in 

 a galvanic pile, as an equal weight of coal by its combustion under a boiler. 

 Indeed it is highly probable, that if we burn under the boiler of a steam engine the 

 quantity of coal required for smelting the zinc from its ores, we shall produce far 

 more force than the whole of the zinc so obtained could originate in any form of 

 apparatus whatever. 



Heat, electricity, and magnetism, have a similar relation to each other as tho 

 chemical equivalents of coal, zinc, and oxygen. By a certain measure of electricity 

 we produce a corresponding proportion of heat or of magnetic power ; we obtain 

 that electricity by chemical affinity, which in one shape produces heat, in another 

 electricity or magnetism. A certain amount of affinity produces an equivalent of 

 electricity in the same manner as, on the other hand, we decompose equivalents of 

 chemical compounds by a definite measure of electricity. The magnetic force of the 

 pile is therefore limited to the extent of the chemical affinity, and in the case before 

 us is obtained by the combination of the zinc aud sulphuric acid. In the combus- 

 tion of coal, the heat results from, and is measured by, the affinity of the oxygen 

 of the atmosphere for that substance. 



It is true that, with a very small expense of zinc, we can make an iron wire a 

 magnet capable of sustaining a thousand pounds weight of iron : let us not allow 

 ourselves to be misled by this. Such a magnet could not raise a single pound 

 weight of iron two inches, and therefore could not impart motion. The magnet 

 acts like a rock, which, while at rest, presses with a weight of a thousand pounds 

 upon a basis : it is like an enclosed lake, without an outlet and without a fall. But 

 it may be said, we have by mechanical arrangements given it an outlet and a fall. 

 True ; and this must be regarded as a great triumph of mechanics ; and I believe it is 

 susceptible of further improvements, by which greater force may be obtained. But 

 with every conceivable advantage of mechanism, no one will dispute that one 

 pound of coal, under the boiler of a steam engine, will give motion to a mass 

 several hundred times greater than a pound of zinc in the galvanic pile. 



Our experience of the employment of electro-magnetism as a motory power is, 

 however, too recent to enable us to foresee the ultimate results of contrivances to 

 apply it ; and, therefore, those who have devoted themselves to solve the problem 

 of its application should not be discouraged, inasmuch as it would undoubtedly be 

 a most important achievement to supersede the steam engine, and thus escape the 

 danger of railroads, even at double their expense. 



Professor Weber of Gottingen has thrown out a suggestion, that if a contrivance 

 could be devised to enable us to convert at will the wheels of the steam carriage 



