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Liebig's Chemical Letters



My dear Sir,

    One of the most influential causes of improvementin the social condition of mankind is that spirit of enterprise which induces menof capital to adopt and carry out suggestions for the improvement of machinery, thecreation of new articles of commerce, or the cheaper production of those alreadyin demand; and we cannot but admire the energy with which such men devote their talents,their time, and their wealth, to realise the benefits of the discoveries and inventionsof science. For even when these are expended upon objects wholly incapable of realisation,- nay, even when the idea which first gave the impulse proves in the end to be altogetherimpracticable or absurd, immediate good to the community generally ensues; some usefuland perhaps unlooked-for result flows directly, or springs ultimately, from exertionsfrustrated in their main design. Thus it is also in the pursuit of science. Theorieslead to experiments and investigations; and he who investigates will scarcely everfail of being rewarded by discoveries. It may be, indeed, the theory sought to beestablished is entirely unfounded in nature; but while searching in a right spiritfor one thing, the inquirer may be rewarded by finding others far more valuable thanthose which he sought.

    At the present moment, electro-magnetism, asa moving power, is engaging great attention and study; wonders are expected fromits application to this purpose. According to the sanguine expectations of many persons,it will shortly be employed to put into motion every kind of machinery, and amongstother things it will be applied to impel the carriages of railroads, and this atso small a cost, that expense will no longer be matter of consideration. Englandis to lose her superiority as a manufacturing country, inasmuch as her vast storeof coals will no longer avail her as an economical source of motive power. "We,"say the German cultivators of this science,"have cheap zinc, and, how smalla quantity of this metal is required to turn a lathe, and consequently to give motionto any kind of machinery!"

    Such expectations may be very attractive, andyet they are altogether illusory! they will not bear the test of a few simple calculations;and these our friends have not troubled themselves to institute.

    With a simple flame of spirits of wine, undera proper vessel containing boiling water, a small carriage of 200 to 300 pounds weightcan be put into motion, or a weight of 80 to 100 pounds may be raised to a heightof 20 feet. The same effects may be produced by dissolving zinc in dilute sulphuricacid in a certain apparatus. This is certainly an astonishing and highly interestingdiscovery; but the question to be determined is, which of the two processes is theleast expensive?

    In order to answer this question, and to judgecorrectly of the hopes entertained from this discovery, let me remind you of whatchemists denominate "equivalents." These are certain unalterable ratiosof effects which are proportionate to each other, and may therefore be expressedin numbers. Thus, if we require 8 pounds of oxygen to produce a certain effect, andwe wish to employ chlorine for the same effect, we must employ neither more nor lessthan 35ù5 pounds weight. In the same manner, 6 pounds weight of coal are equivalentto 32 pounds weight of zinc. The numbers representing chemical equivalents expressvery general ratios of effects, comprehending for all bodies all the actions theyare capable of producing.

    If zinc be combined in a certain manner withanother metal, and submitted to the action of dilute sulphuric acid, it is dissolvedin the form of an oxide; it is in fact burned at the expense of the oxygen containedin the fluid. A consequence of this action is the production of an electric current,which, if conducted through a wire, renders it magnetic. In thus effecting the solutionof a pound weight, for example, of zinc, we obtain a definite amount of force adequateto raise a given weight one inch, and to keep it suspended; and the amount of weightit will be capable of suspending will be the greater the more rapidly the zinc isdissolved.

    By alternately interrupting and renewing thecontact of the zinc with the acid, and by very simple mechanical arrangements, wecan give to the iron an upward and downward or a horizontal motion, thus producingthe conditions essential to the motion of any machinery.

    This moving force is produced by the oxidationof the zinc; and, setting aside the name given to the force in this case, we knowthat it can be produced in another manner. If we burn the zinc under the boiler ofa 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 galvanicpile, or that in this mode of generating force less loss is sustained, - we muststill recollect the equivalents of zinc and coal, and make these elements of ourcalculation. According to the experiments of Despretz, 6 pounds weight of zinc, incombining with oxygen, develops no more heat than 1 pound of coal; consequently,under equal conditions, we can produce six times the amount of force with a poundof coal as with a pound of zinc. It is therefore obvious that it would be more advantageousto employ coal instead of zinc, even if the latter produced four times as much forcein 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-enginethe quantity of coal required for smelting the zinc from its ores, we shall producefar more force than the whole of the zinc so obtained could originate in any formof apparatus whatever.

    Heat, electricity, and magnetism, have a similarrelation to each other as the chemical equivalents of coal, zinc, and oxygen. Bya certain measure of electricity we produce a corresponding proportion of heat orof magnetic power; we obtain that electricity by chemical affinity, which in oneshape produces heat, in another electricity or magnetism. A certain amount of affinityproduces an equivalent of electricity in the same manner as, on the other hand, wedecompose equivalents of chemical compounds by a definite measure of electricity.The magnetic force of the pile is therefore limited to the extent of the chemicalaffinity, and in the case before us is obtained by the combination of the zinc andsulphuric acid. In the combustion of coal, the heat results from, and is measuredby, the affinity of the oxygen of the atmosphere for that substance.

    It is true that with a very small expense ofzinc, we can make an iron wire a magnet capable of sustaining a thousand pounds weightof iron; let us not allow ourselves to be misled by this. Such a magnet could notraise 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 thousandpounds upon a basis; it is like an inclosed lake, without an outlet and without afall. But it may be said, we have, by mechanical arrangements, given it an outletand a fall. True; and this must be regarded as a great triumph of mechanics; andI believe it is susceptible of further improvements, by which greater force may beobtained. But with every conceivable advantage of mechanism, no one will disputethat one pound of coal, under the boiler of a steam-engine, will give motion to amass several hundred times greater than a pound of zinc in the galvanic pile.

    Our experience of the employment of electro-magnetismas a motory power is, however, too recent to enable us to foresee the ultimate resultsof contrivances to apply it; and, therefore, those who have devoted themselves tosolve the problem of its application should not be discouraged, inasmuch as it wouldundoubtedly be a most important achievement to supersede the steam-engine, and thusescape the danger of railroads, even at double their expense.

    Professor Weber of G”ttingen has thrown outa suggestion, that if a contrivance could be devised to enable us to convert at willthe wheels of the steam-carriage into magnets, we should be enabled to ascend anddescend acclivities with great facility. This notion may ultimately be, to a certainextent, realised.

    The employment of the galvanic pile as a motorypower, however, must, like every other contrivance, depend upon the question of itsrelative economy: probably some time hence it may so far succeed as to be adoptedin certain favourable localities; it may stand in the same relation to steam poweras the manufacture of beet sugar bears to that of cane, or as the production of gasfrom oils and resins to that from mineral coal.

    The history of beet-root sugar affords us anexcellent illustration of the effect of prices upon commercial productions. Thisbranch of industry seems at length, as to its processes, to be perfected. The mostbeautiful white sugar is now manufactured from the beet-root, in the place of thetreacle-like sugar, having the taste of the root, which was first obtained; and insteadof 3 or 4 per cent., the proportion obtained by Achard, double or even treble thatamount is now produced. And notwithstanding the perfection of the manufacture, itis probable it will ere long be in most places entirely discontinued. In the years1824 to 1827, the prices of agricultural produce were much lower than at present,while the price of sugar was the same. At that time one malter1 of wheat was 10s.,and one klafter2 of wood 18s., and land was falling in price. Thus, food and fuelwere cheap, and the demand for sugar unlimited; it was, therefore, advantageous togrow beet-root, and to dispose of the produce of land as sugar. All these circumstancesare now different. A malter of wheat costs 18s.; a klafter of wood, 30s. to 36s.Wages have risen, but not in proportion, whilst the price of colonial sugar has fallen.Within the limits of the German commercial league, as, for instance, at Frankfort-on-the-Maine,a pound of the whitest and best loaf sugar is 7d.; the import duty is 3d.,or 30s. per cwt., leaving 3d. as the price of the sugar. In the year 1827,then, one malter of wheat was equal to 40 lbs. weight of sugar, whilst at presentthat quantity of wheat is worth 70 lbs. of sugar. If indeed fuel were the same inprice as formerly, and 70 lbs. of sugar could be obtained from the same quantityof the root as then yielded 40 lbs., it might still be advantageously produced; butthe amount, if now obtained by the most approved methods of extraction, falls farshort of this; and as fuel is double the price, and labour dearer, it follows that,at present,it is far more advantageous to cultivate wheat and to purchase sugar.

    There are, however, other elements which mustenter into our calculations; but these serve to confirm our conclusion that the manufactureof beet-root sugar as a commercial speculation must cease. The leaves and residueof the root, after the juice was expressed, were used as food for cattle, and theirvalue naturally increased with the price of grain. By the process formerly pursued,75 lbs. weight of juice were obtained from 100 lbs. of beet-root, and gave 5 lbs.of sugar. The method of Sch*tzenbach, which was eagerly adopted by the manufacturers,produced from the same quantity of root 8 lbs. of sugar; but it was attended withmore expense to produce, and the loss of the residue as food for cattle. The increasedexpense in this process arises from the larger quantity of fuel required to evaporatethe water; for instead of merely evaporating the juice, the dry residue is treatedwith water, and we require fuel sufficient to evaporate 106 lbs. of fluid insteadof 75 lbs., and the residue is only fit for manure. The additional 3 lbs. of sugarare purchased at the expense of much fuel, and the loss of the residue as an articleof food.

    If the valley of the Rhine possessed mines ofdiamonds as rich as those of Golconda, Visiapoor, or the Brazils, they would probablynot be worth the working: at those places the cost of extraction is 28s. to 30s.the carat. With us it amounts to three or four times as much - to more, in fact,than diamonds are worth in the market. The sand of the Rhine contains gold; and inthe Grand Duchy of Baden many persons are occupied in gold-washing when wages arelow; but as soon as they rise, this employment ceases. The manufacture of sugar frombeet-root, in the like manner, twelve to fourteen years ago offered advantages whichare now lost: instead, therefore, of maintaining it at a great sacrifice, it wouldbe more reasonable, more in accordance with true natural economy, to cultivate otherand more valuable productions, and with them purchase sugar. Not only would the statebe the gainer, but every member of the community. This argument does not apply, perhaps,to France and Bohemia, where the prices of fuel and of colonial sugar are very differentto those in Germany.

    The manufacture of gas for lighting, from coal,resin, and oils, stands with us on the same barren ground.

    The price of the materials from which gas ismanufactured in England bears a direct proportion to the price of corn: there thecost of tallow and oil is twice as great as in Germany, but iron and coal are two-thirdscheaper; and even in England the manufacture of gas is only advantageous when theother products of the distillation of coal, the coke, &c., can be sold.

    It would certainly be esteemed one of the greatestdiscoveries of the age if any one could succeed in condensing coal gas into a white,dry, solid, odourless substance, portable, and capable of being placed upon a candlestick,or burned in a lamp. Wax, tallow, and oil, are combustible gases in a solid or fluidform, which offer many advantages for lighting, not possessed by gas: they furnish,in well-constructed lamps, as much light, without requiring the expensive apparatusnecessary for the combustion of gas, and they are generally more economical. In largetowns, or such establishments as hotels, where coke is in demand, and where lossesin stolen tallow or oil must be considered, together with the labour of snuffingcandles and cleaning lamps, the higher price of gas is compensated. In places wheregas can be manufactured from resin, oil of turpentine, and other cheap oils, as atFrankfort, this is advantageous so long as it is pursued on small scale only. Iflarge towns were lighted in the same manner, the materials would rise in price: thewhole amount at present produced would scarcely suffice for two such towns as Berlinand Munich. But no just calculation can be made from the present prices of turpentine,resin, &c., which are not produced upon any large scale.



    1.Malter - a measure containing several bushels,but varying in different countries.


    2.Klafter - a cord, a stack, measuring six feetevery way.