LIEBIG ' S LETTERS ON CHEMISTRY.

THESE Letters were originally written to call the attention of the public, and more especially of the Governments of Germany, to the practical importance of chemical science, with the ulterior view of stimulating them to establish schools of chemistry. As success seems to have attended his efforts in Germany, Professor LIEBIG was induced to prepare an English edition, with some additional letters; and the result appears in the little volume before us, whose manuscript and proofs have been revised by Dr. GARDNER.

The book is well designed to accomplish its purpose of exciting to the study of chemistry, by showing the importance of that science to the useful arts, to agriculture, and to the health of man. It does not attempt to teach the practice or scarcely the prin- ciples of the science, but is an exposition of the most striking points of chemistry as they bear upon the interests of men and nations. Something short of this has been aimed at before : we have had wonders, or striking facts, not only in chemistry but in many other sciences, popularly exhibited, and very cleverly exhi- bited too. These were, however, for the most part isolated, barren, or incomplete. The wonders were very wonderful, the facts very curious or amusing ; but when they were read of or even per- formed,`the performers " were but where they were" ; and though a taste for science might be indirectly fostered, and the pur- suit was morally healthful and occupying, it was perhaps ob- noxious to the cynical censure of JOHNSON respecting the amateur chemists of his day—rational creatures pass the morning in mingling different bodies to produce a known result, and when the effect corresponds with the expectation, say it is strange, and iniugle them again. But LIEBIG'S Familiar Letters on Chemistry display the power, ease, and purpose of a master dealing with the essential characteristics of his own art, untrammelled by those details which a formal exposition of principles for the purpose of instruction necessitate. A small volume contains the pith of his two great works on Agricultural and Physiological Chemistry, presented in a more popular style than might consist with the gravity of a scientific treatise.

The little exposition of chemical science that the book contains is allusive rather than direct. A brief account of the elements of matter, and a slight but masterly expression of the mutability of all things—that the chemist recognizes " nothing unchangeably solid, liquid, or steriform"—with a panegyric on cork, glass, caoutchouc, and platinum, as the chemist's instruments of action—complete the introductory matter. The rest of the volume explains by practical illustrations the extraordinary sources of national wealth and uni- versal benefits that have been opened up by modern chemistry, in facilitating the production of articles of necessary use, and adding value to substances previously worthless and wasted. The next part shows that life itself both in plants and animals is a che- mical process, dependent upon the properties of the food we take, and ultimately carried on by means of atmospheric air; which, if food be withheld or the organs cannot properly assimilate it, is the agent that ultimately destroys us, by gradually dissipating all the fleshy parts of the body,—the animal, in fact, breathing out its own flesh till death ensues, just as a lighted lamp exhausts its sup- ply. The third part considers chemistry as it may be usefully applied to agriculture, and deals with it in the same general and comprehensive way : showing the elements on which vegetation depends; the manner in which mechanical means—as ploughing— operate upon the soil; the different result of different manures on different kinds of crops; and the useful properties of one class over another, not merely in the quantity of nutritive matter they furnish for food, but in the substances they enable the agriculturist to return to the soil in the shape of composts. The letters in which the waste of manure in Great Britain and the present state of our

soil and agriculture are alluded to, are well worth the careful atten- tion of every one who may not have studied the author's larger work on Agricultural Chemistry, and even of those who have, on account of the additional remarks.

The merit of the book in a literary point of view is the complete- ness, ease, and spirit of its expositions. It combines the science of the philosopher with the popular powers of the mere litterateur, whose trade it is to clothe the ideas of others in an attractive form.

The occasional defect of the book is that it deals a shade too much in essences; presenting some of the more purely chemical axioms in too condensed a form to be digested by untrained faculties, without more trouble than they may be disposed to undergo. Considered merely as composition, the most successful part of

the Letters is the exposition of the effects that have sprung from "the manufacture of soda from common culinary salt." For fulness of matter, variety of illustration, singularity of ramification, and completeness of result, it approaches ADAM SMITH'S celebrated explanation of the "division of labour." Though the whole is not long, it is too long for our pages; but we will take a few passages.

&IDA AND SOAP.

Soda has been used from time immemorial in the manufacture of soap and glass, two chemical productions which employ and keep in circulation an im- mense amount of capital. The quantity of soap consumed by a nation would be no inaccurate measure whereby to estimate its wealth and civilization. Of two countries, with an equal amount of population, the wealthiest and most highly civilised will consume the greatest weight of soap. This consumption does not subserve sensual gmttifieatton, nor depend upon fashion, but upon the filing of the beauty, comfort, and welfare attendant upon cleanliness; and a to this feeling is coincident with wealth and civilization. The tick is the middle ages concealed a want of cleanliness in their clothes and persons under a profusion of costly scents and essences, whilst they were more luxu- rious in eating and drinking, in apparel and horses. With us a want of clean- liness is equivalent to insupportable misery and misfortune.

Soap belongs to those manufactured products, the money value of which continually disappears from circulation, and requires to be continually renewed. It is one of the few substances which are entirely consumed by use, leaving no product of any worth. Broken glass and bottles are by no means absolutely worthless ; for rags we may purchase new cloth ; but soap-water has no value whatever. It would be interesting to know accurately the amount of capital involved in the manufacture of soap : it is certainly as large as that employed in the coffee•trade, with this important difference as respects Germany, that it is entirely derived from our own soil.

France formerly imported soda from Spain, Spanish soda being of the best quality, at an annual expenditure of twenty to thirty millions of francs. During the war with England, the price of soda, and consequently of soap and glass, rose continually ; and all manufactures suffered in consequence.

The present method of making soda from common salt was discovered by Le Blanc, at the end of the last century. It was a rich boon for France, and be- came of the highest importance during the wars of Napoleon. In a very short time it was manufactured to an extraordinary extent, especially at the seat of the soap-manufactories. Marseilles possessed for a time a monopoly of soda and soap. The policy of Napoleon deprived that city of the advantages derived from this great source of commerce, and thus excited the hostility of the popu- lation to his dynasty, which became favourable to the restoration of the Bour- bons. A carious result of an improvement in a chemical manufacture. It was not long, however, in reaching England.

In order to prepare the soda of commerce (which is the carbonate) from common salt, it is first converted into Glauber's salt (sulphate of soda.) For this purpose, SO pounds weight of concentrated sulphuric acid (oil of vitriol) are required to 100 pounds of common salt.

EFFECTS OF A TRAVELLER'S DISCOVERY.

Saltpetre being indispensable in making sulphuric acid, the commercial value of that salt had formerly an important influence upon its price. It is true that 100 pounds of saltpetre only are required to 1,000 pounds of sulphur: but its coat was four times greater than an equal weight of the latter. Travellers had observed, near the small seaport of Yquiqui, in the district of Atacama, in Peru, an efflorescence covering the ground over extensive dis- tricts. This was found to consist principally of nitrate of soda. Advantage was quickly taken of this discovery. The quantity of this valuable salt proved to be inexhaustible, as it exists iu beds extending over more than two hundred square miles. It was brought to England at less than half the freight of the East India saltpetre (nitrate of patassa); and as, in the chemical manufacture, neither the potash nor the soda were required, but only the nitric acid in com- bination with the alkali, the soda-saltpetre of South America soon supplanted the potash-nitre of the East. The manufacture of sulphuric acid received a new impulse; its price was much diminished, without injury to the manufac- turer; and, with the exception of fluctuations caused by the impedimenta thrown in the way of the export of sulphur from Sicily, it soon became reduced to a minimum, and remained stationary. Potash•saltpetre is now only employed in the manufacture of gunpowder ; it is no longer in demand for other purposes ; and thus, if Government effect a saving of many hundred thousand pounds annually in gunpowder, this economy must be attributed to the increased manufacture of sulphuric acid.

snr.rnua: A HINT TO MONOPOLIST& Reflecting upon the important influence which the price of sulphur exercises, upon the cost of production of bleached and printed cotton stuffs, soap, glass, &c., and remembering that Great Britain supplies America, Spain, Portugal, and the East, with these, exchanging them for raw cotton, silk, wine, raisins, indigo, &c. &c., we can understand why the English Government should have resolved to resort to war with Naples, in order to abolish the sulphur monopoly, which the latter power attempted recently to establish. Nothing could be more opposed to the true interests of Sicily than such a monopoly : indeed, had it been maintained a few years, it is highly probable that sulphur, the source of her wealth, would have been rendered perfectly valueless to her. Science and industry form a power to which it is dangerous to present impediments. It was not difficult to perceive that the issue would be the entire cessation of the exportation of sulphur from Sicily. In the short period the sulphur monopoly lasted, fifteen patents were taken out for methods to obtain back the sulphuric acid used in making soda. Admitting that these fifteen experiments were not perfectly successful, there can be no doubt it would ere long have been accom- plished. But then, in gypsum, (sulphate of lime,) and in heavy spar, (sulphate of barytes,) we possess mountains of sulphuric acid ; in galena, (sulphate of lead,) and iu iron pyrites, we have no less abundance of sulphur. The problem is, how to separate the sulphuric acid, or the sulphur, from these native stores. Hundreds of thousands of pounds weight of sulphuric acid were prepared from iron pyrites, while the high price of sulphur consequent upon the monopoly lasted. We should probably ere long have triumphed over all difficulties, and have separated it from gypsum. The impulse has been given, the possibility of the process proved ; and it may happen in a few years that the inconsiderate financial speculation of Naples may deprive her of that lucrative commerce.

The section least satisfactory in its practical results is that which relates to the nutrition of man ; in part because the author is some- what general, in part because his views as put forth in Animal Chemistry have been exhibited by compilers upon a larger scale than he has now done, and partly perhaps because all who can get them eat bread and meat with vegetables, and drink wine, beer, or spirits, having instinctively jumped to the late and laborious demonstrations of science. The section on Agriculture has been as extensively reproduced as that on Physiology, but with less of a forestalling effect ; and we think LTEBIG has thrown in new matter. As a sample of this part, we will quote a passage of import in regard to the agriculture of our own country.

AGRICULTURAL IMPORTANCE OF PHOSPHATES.

In order to furnish you with a clear idea of the importance of the phos- phates, it may be sufficient to remind you of the fact, that the blood of man and animals, besides common salt, always contains alkaline and earthy phos- phates. If we burn blood and examine the ashes which remain, we find certain parts of them soluble in water, and others insoluble. The soluble parts me common salt and alkaline phosphates; the insoluble consist of phosphate of

lime, phosphate of magnesia, and oxide of iron. • •

It is a most curious fact, that if we incinerate grain or its flour, peas, beaus, and lentils, we obtain ashes, which are distinguished from the ashes of all other parts of vegetables by the absence of alkaline carbonates. The ashes of these seeds, when recently prepared, do not effervesce with acids: their soluble in- gredients consist solely of alkaline phosphates—the insoluble parts of phosphate of lime, phosphate of magnesia, and oxide of iron; consequently, of the very same salts which are contained in blood, and which are absolutely indispensable to its formation. We are thus brought to the further indisputable conclusion, that no seed suitable to become food for man and animals can be formed in sly plant without the presence and cooperation of eke phosphates. A Gehl IR which phosphate of lime or the alkaline phosphates form no part of the soil, is totally incapable of producing grain, peas, or beans.

An enormous quantity of these substances, indispensable to tho nourish- ment of plants, is annually withdrawn from the soil, and carried into great towns, in the shape of flour, cattle, &c. It is certain that this incessant re- moval of the phosphates must tend to exhaust the land and diminish its capa- bility of producing grain. The fields of Great Britain are in a state of pro- gressive exhaustion from this cause ; as is proved by the rapid extension of the cultivation of turnips and mange' wurzcl—plants which contain the least amount of the phosphates, and therefore require the smallest quantity for their development. These roots contain 80° to 92° per cent of water. Their great bulk makes the amount of produce fallacious as respects their adapta- tion to the food of animals, inasmuch as their contents of the ingredients of the blood, i. e. of substances which can be transformed into flesh, stands in a direct ratio to their amount of phosphates, without which neither blood nor flesh can be formed.

Our fields will become more and more deficient in these essential ingre- dients of food, in all localities where custom and habits do not admit the col- lection of the fluid and solid excrements of man, and their application to the purposes of agriculture. In a former letter I showed you how great a waste of phosphates is unavoidable in England, and referred to the well-known fact that the importation of bones restored in a most admirable manner the fertility of the fields exhausted from this cause.

Another proof of the efficacy of the phosphates in restoring fertility to exhausted land is afforded by the use of the guano—a manure which, although of recent introduction into England, has found such general and extensive application. • • • • • • If it were possible to restore to the soil of England and Scotland the phosphates which during the last fifty years have been carried to the sea by the Thames and the Clyde, it would be equivalent to manuring with millions of hundredweights of bones; and the produce of the land would increase one- third, or perhaps double itself, in fire to ten years.

We cannot doubt that the Caine result would follow if the price of the guano admitted the application of a quantity to the surface of the fields, con- taining as much of the phosphates as have been withdrawn from them in the same period.

If a rich and cheap source of phosphate of lime and the alkaline phos- phates were open to England, there can be no question that the importation of foreign corn might be altogether dispensed with after a short time. For these materials England is at present dependent upon foreign countries ; and the high price of guano and of bones prevents their general application and in sufficient quantity. Every year the trade in these substances must decrease, or their price will rise as the demand for them increases.

According to these premises, it cannot he disputed, that the annual ex- pense of Great Britain for the importation of bones and guano is equivalent to a duty on corn ; with this difference only, that the amount is paid to foreigners in money.

To restore the disturbed equilibrium of the constitution of the soil—to fertilize her fields—England requires an enormous supply of animal excre- ments ; and it must therefore excite considerable interest to learn, that she possesses beneath her soil beds of fossil guano, strata of animal excrements, in a state which will probably allow of their being employed as a manure at a very small expense. The coproliihes discovered by Dr. Backland, (a dis- covery of the highest interest to geology,) are these excrements ; and it seems extremely probable, that in these strata England possesses the means of supply- ing the place of recent bones, and therefore the principal conditions of im- proving agriculture—of restoring and exalting the fertility of her fields.