LI33RARY OF THE UNIVERSITY OF CALIFORNIA. Class FAMILIAE LETTERS CHEMISTRY, IN ITS RELATIONS TO PHYSIOLOGY, DIETETICS, AGRICULTURE, COMMERCE, AND POLITICAL ECONOMY. JUSTUS VON LIEBIG. FOURTH EDITION, REVISED AND ENLARGED. EDITED BY JOHN BLYTH, M.D., PROFESSOR OK CHEMISTRY IN QUEEN'S COLLEGE, CORK. LONDON: WALTON AND MABERLY, UPPER GOWER STREET, & IVY LANE, PATERNOSTER ROW. 1859. LONDON : BRADBURY AND EVANS, PRINTERS, WHITEFRIARS. - OF I SIR JAMES CLARK, BART., M.D., F.R.8., PHYSICIAN TO THE QUEEN AND HIS ROYAL HIGHNESS PRINCE ALBERT, &C. MY DEAR SIR JAMES, A MINISTER of the British Crown, in addressing the House of Commons, described the social state of your country in the following terms : " We have shown the example of a nation, in which every class of society accepts with cheer- fulness the lot which Providence has assigned to it ; while at the same time every individual of each class is constantly striving to raise himself in the social scale, not by injustice and wrong, not by violence and illegality ; but by perse- vering good conduct, and by the steady and energetic exertion of the moral and intellectual faculties, with which his Creator has endowed him." * You, too, my dear Sir James, are one of those men who, impressed with a strong feeling of what is required for the progressive improvement of society, devote their powers to the welfare of their country. By your persevering exertions, aided by others entertaining similar views, and, supported by the patronage of an enlightened Prince, who sees in the advance- ment of science the nation's good, you have succeeded in establishing in your Metropolis an Institution the Royal * Lord Palmerston's Speech, June 25th, 1850. iv DEDICATION. College of Chemistry which affords ample opportunities, under an able teacher, to all who desire to become prac- tically acquainted with the various departments of the science to which I have devoted my life, and in the progress of which the prosperity and happiness of nations is so intimately involved. Allow me, whom you will scarcely consider a foreigner, since I am proud to be enabled to call myself a freeman of two of your most important cities allow me, my dear Sir James, to express to you the thanks which Science owes you, by placing your name at the head of a work, the object of which is to make known to a wide circle the recent pro- gress of Chemistry, and to explain the principles of natural science in some of their most important applications. I remain, my dear Sir James, Very sincerely yours, JUSTUS VON LIEBIG. PREFACE. BESIDES extending considerably the former Letters, I have in the present edition added a number of new letters, which refer to general scientific questions and to the most remarkable discoveries recently made in the departments of chemistry and physics. Among these are letter 2nd, on the Study of the Natural Sciences ; letter 13th, on the Correlation of the Forces of Inorganic Nature ; letter 15th, on the Alteration of Properties in Bodies ; letter 23rd, on Materialism in Connection with Natural Inquiries. Some investigations which I instituted last year on soils, and their comportment with the soluble food of plants, which were principally occasioned by the ex- cellent papers of Way, have led to new and unex- pected views of the nutrition of plants, and of their mode of absorbing food. Further, a series of experiments on cultivation has been undertaken by many agricul- tural societies in Germany, and particularly by the general committee of the Agricultural Society of Bavaria, in which I took part. The experimental results thus obtained, induced me to discuss more fully, certain highly important agricultural questions indicated in the 35th letter of the former edition. I have embodied my con- vi PREFACE. elusions in a separate series of agricultural chemical letters on " Theoretical and Practical Agriculture," to which I must refer the reader. My friend Dr. Gregory, who assisted me in the former editions, has, meantime, heen removed hy a Higher Power from his family and from science. United for more than twenty years by the ties of a sincere and intimate friend- ship, no one feels more keenly than I do, the great loss sustained by his friends in his death. Rare extent of knowledge, combined with admirable powers of mind, enabled him to apprehend exactly the ideas and views of others, and to put them forward in the best form, and with the precision of original composition. I have requested Dr. Blyth, professor of Chemistry, Queen's College, Cork, my friend and former pupil, to edit the present edition of my Letters. Dr. Blyth is one of the most distinguished Chemists of Great Britain. From his intimate acquaintance with chemical science, and with the different subjects discussed in these Letters, I esteem myself fortunate, that he has in the kindest manner acceded to my wishes. JUSTUS VON LIEBIG. MUNICH, Nov. 10th, 1858. CONTENTS. LETTER I. PAGE Importance of Chemistry Its rank among sciences Recent origin of modern Chemistry Like Mathematics and Physics, Chemistry is a language, an instrument, which can only lead to discovery in the hands of genius Chemical analysis Applied Chemistry Theory of Chemistry Chemical processes and analysis are the foundation of all the rest of the science Chemistry essential to the future progress of Medicine, . Geology and Physiology Philo- sophical method of research into the vital phenomena Great advantages already derived from Chemistry ..... 1 LETTER II. The Inductive and Aristotelian philosophy compared The true mode of investigating nature, and of explaining natural phenomena Observation and reflection necessary to success The art of observ- ing requires practice and training Value of experiments to ascer- tain natural laws Theory and practice contrasted Problems proposed to be solved by Chemistry Philosophical relations of Chemistry Immensity of the universe Mind the cause of motion Importance of the study of natural laws, such as those of Chemical Combination .......... 23 LETTER III. Origin and progress of Chemistry The Philosopher's Stone and the Transmutation of Metals Alchemy and the Alchemists Learning of the Alchemists True nature of Alchemy, it was the Chemistry of the period The wonders of modern science exceed the wildest dreams of Alchemists The theory of Phlogiston useful at the time in classifying facts and in generalisation Stahl Cavendish Black Lavoisier The Anti -phlogistic Theory The three periods of Science 37 LETTER IY. Teaching of the Dark Ages Opposition to new ideas Columbus Copernicus Invention of Printing Universities founded Galileo viii CONTENTS. PAGE Overthrow of Galenic Medicine Doctrines of Aristotle System of Galen Elements of the Alchemists The Universal Medicine Paracelsus Medical Chemistry. Later Medical Theories . . 63 LETTER Y. Chemical Combination and Decomposition Chemical Affinity Influ- ence of Heat, Cohesion, and other forces Solubility Use of Solvents in Analysis 86 LETTER VI. Chemical Equivalents Definite Proportions Multiple Proportions Method of calculating from analysis, the relative numbers of the equivalents of the different Elements of a Compound. Chemical Symbols Examples Acids and Bases Chemical Formula How determined Examples 93 LETTER VII. Cause of definite proportions Atomic Theory Definition of Physical and Chemical Atoms ; practically indivisible by mechanical and chemical means respectively. Compound Atoms or Molecules Atomic Weights Distinction between the facts and the hypothesis 103 LETTER YIII. Form of Atoms or Molecules Isomorphism Isomorphous groups Specific Gravity Atomic Volumes . . . . . .111 LETTER IX. Chemical Implements Glass Cork Platinum Their importance to the Chemist The Balance equally indispensable Analysis of Minerals Artificial production of Minerals Chemical Synthesis Physiological Chemistry the Problem of the present day . .124 LETTER X. Solids, Liquids, Gases, are not permanent states of Matter Liqui- faction and Solidification of Gases Solid Carbonic Acid The Spheroidal State True Explanation of the Experiments of Leiden- frost and Boutigny Condensation of Gases on the surface of Solid Bodies Charcoal Spongy Platinum Manufacture of Oil of Vitriol and of Vinegar in this way The Nascent state of Bodies . . 1 29 LETTER XL Importance of the manufacture of Soda from Salt Oil of Vitriol ; its CONTENTS. ix PAGE importance Uses of Oil of Vitriol in preparing Soda Muriatic Acid, Bleaching Powder, Bone Glue Manufacture of Glass Pre- paration of the Soluble Glass of Fuchs Its applications Use of Oil of Vitriol in refining Silver : in preparing Superphosphate of Lime, &c. Importance to England of the Sulphur trade . .141 LETTER XII. Electricity as a motive power Expense of it ; and of Zinc compared with Coals Comparative cost of Beet-root and of Cane Sugar Prospects of both Continental tax on Colonial Sugar Position of the manufacture of Gas from resin, oils, coals and wood . .154 LETTER XIII. Machines do not create power Belief in perpetual motion founded in error Mayer's views of the nature of force or power Motion and heat are convertible into each other Interesting application of this fact Electricity as a motive power can be measured in the same way as heat Its power also measured by the decompo- sition of water By the vital processes of plants the heat of the sun's rays becomes latent Food of animals destined for nutrition and for the production of heat The chemical changes in the consti- tuents of the body are the causes of motion 165 LETTER XIY. Isomerism Polymerism Examples Crystallisation Amorphous bodies Allotropic transformations of elements and compounds . . 176 LETTER XY. Allotropic States of Bodies Ozonised Oxygen, its preparation, remark- able properties, and mode of detection Its destruction by heat Preparation of Ozone by oxidation of Bitter Almonds, Oil of Tur- pentine, Sulphurous Acid, &c. Spongy Platinum ozonises Oxygen An explanation of the transformations of Oxygen not possible in the present state of science The properties of Ozone are acquired by chemical action Application of Brodie's views of chemical action to explain the ozonising of Oxygen 182 LETTER XYI. Chemical Attraction forms the substance of organised bodies Influ- ence upon it of Light, Heat, Cohesion, Gravity, and the Vital Force Action of Heat, both on Inorganic and Organic Bodies Disturbance of equilibrium Direction of Attraction Organic Atoms or Molecules No element, as such, can serve as food for a plant or animal ''- /^ . . . . . .193 x CONTENTS. LETTER XYII. PAGE Origin of Organic Atoms ; from Carbonic Acid, Water, and Ammonia Derivation of non-azotised Vegetable Products from Carbonic Acid and Water by Deoxidation Coupled Compounds Decay of Organic Bodies, caused by the action of Oxygen, as seen in cut fruit Putrefaction and Fermentation defined and described Vinous Fermentation of Sugar Heat modifies Fermentation Ferments Flavour of Wines and Spirits 202 LETTER XYIII. Vegetable Caseine and the Emulsion of Almonds as Ferments Effects of the latter body on Salicine and Araygdaline Oil of Mustard Gluten of Flour as a Ferment Transformation of Starch into Gum and Sugar Germination and Malting Maturation of Fruits Skin and membranes agree in many properties with Gluten and Yeast Making of Cheese Action of the Lining Membrane of the Stomach in Digestion Pepsine does not exist Theory of the Action of Ferments Various kinds of Ferments . . . - .218 LETTER XIX. Oxygen is the exciting cause of Putrefactive Transformations, all of which begin wkh Decay or slow Combustion Eremacausis, or decay, is a process of combustion at the common temperature Examples of Eremacausis in Bleaching ; Decay of animal matter Decay or Eremacausis of Alcohol ; Acetification, Nitrification, the Eremacausis of Ammonia Making of Wines : of Beer Bavarian Beer : cause of its superiority Application of the same to hasten the Ripening of Wines. . . . . . . 232 LETTER XX. Boiling checks fermentation Preservation of meat, fruits, &c., by Appert's process Effect of the introduction into the system of putrescent matters Poisoning from dissection : from bad sausages, &c. Antidotes to these poisons Danger of bad meat . ... 246 LETTER XXI. Theory which ascribes fermentation to Fungi refuted Characters of Yeast Putrefaction not caused by Animalculse ; but decay is hastened by them Parasitic theory of Contagion refuted Scabies Muscardine Limits of Vital and Physical Forces . . .253 LETTER XXII. Connection of the Sciences True Province of Physiology and Che- mistry Chemical and Physiological notions of Blood, Urine, and CONTENTS. PAGE Bile, differ The Vital Force is something more than the known Physical and Chemical forces The Vital Force must co-operate with known forces Little is known of the nature of Physical and Chemical forces Examples Crystallisation of Glauber's Salts Engravings copied by chemical means Action of the blood corpus- cules in respiration. . . 270 LETTER XXIII. In inorganic nature, Mechanical and Chemical Forces predominate The properties of organic substances are due to the order of arrange- ment of their elements In organised beings a peculiar Force is in operation A Vital Force is denied by those only whose know- ledge of Physical Forces is defective The law of Progressive Deve- lopment has no fouudation in nature Views of Bischoff Chemical Forces may form an organic but not an organised body ; the Vital Force alone controlling the Chemical Forces gives rise to the latter Spontaneous generation has no existence in nature Views of the physiological materialists contested A Vital Force recognised . 283 LETTER XXIV. Scientific study of obscure objects Example Origin of the belief in Spontaneous Combustion of the human body Alleged cases of it ill observed The fact assumed on insufficient grounds In all the cases, a light or burning fuel has been in the room, and in no case has the combustion been witnessed Flesh is not combustible till dried, and then it is not combustible like wood Living flesh cannot burn, nor does steeping it in fat or spirits render it com- bustible All nitrogenous compounds are comparatively incom- bustible The Electrical theory is altogether fanciful The sup- posed cases arose generally from intoxication ; the victim of drink falls on the fire or sets fire to the bed or furniture, and is suffocated, and his body partly consumed ....... 296 LETTER XXV. Hopeful prospects of Physiological Science if pursued inductively Mutual relation of natural laws Physical and Chemical Variation of the density and boiling points of liquids according to the variations in their composition Examples Relation of Specific Heat to Com- position ; and to the velocity of sound in gases Relation of Electric Currents to Magnetism, Heat, Chemical Action, &c. Vital pro- perties related to other properties of matter Progress of Anatomical Physiology Anatomy studies the apparatus, but cannot explain the process without Chemistry Province of Chemistry Examples of Chemical explanations of Physiological facts ; as in the Chemistry of the Urine Method of determining Chemical formulae Their true meaning . . . . . . . . . . 323 xii CONTENTS. LETTER XXVI. ^ PAGE Nutritive Substances strictly so called Respiratory food The Oxygen absorbed in the lungs is entirely given out in combination with Carbon and Hydrogen Amount of Carbon daily consumed by an adult' Amount of Oxygen required to convert it into Carbonic Acid Respiration 338 LETTER XXVII. Animal Heat derived from the Oxidation of Carbon and Hydrogen in the Body The Food is Burned in the Body, as Fuel in a Furnace Effects of External Cooling on the amount of Food required to keep up the Heat of the Body A Starving Man soon yields to Cold Clothing compensates to a certain extent for Food Effects of Star- vation ; the Body rapidly Oxidised and Consumed Analogous Phe- nomena in Disease The Solid and Liquid Excreta are not Putres- cent, but partially Oxidised, and represent the Soot, Smoke, and Ashes of a Furnace Compensating Action of Organs ; Kidneys and Intestines ; Lungs and Liver Respiration is the Moving Spring . 344 LETTER XXVIII. Effects of Respiration on the Inspired Air General and Pulmonary Circulation Composition of Expired Air Gases absorbed and given out by the Blood Process of Respiration True Cause of Death from breathing Expired Air Importance of Ventilation Quick-lime may be used as a Substitute One-tenth to One-fourth of the Inspired Oxygen combines with Hydrogen The calculated amount of Heat from the combustion of the known weight of Carbon, and Hydrogen, out of the Body, agrees closely with that obtained by their Oxidation in the Body 354 LETTER XXIX. Nutritious or Plastic Food The Blood; its fibrine, globules, and albumen Its ashes; they contain iron Importance of Albumen ; as in the Egg, it is the foundation of all the Tissues Fibrine and Albumen, Flesh and Blood, are the same in Composition Mus- . cular Fibre, convertible into Albumen, even out of the Body Milk Caseine Its relation to Albumen and Fibrine Nutrition of Carnivora, and of the Suckling Mammalia ; of Graminivora and Herbivora, essentially the same Composition of their Food Vegetable Albumen, Fibrine, and Caseine identical with the corres- ponding Animal Substances Vegetables produce the food of Animals Animals destroy this Food, and return it to the Air and Soil, as Carbonic Acid, Water, Ammonia, and Salts, to serve again as food for Plants Products of the Oxidation of Albumen, &c. Plastic, or Nitrogenous, or Sanguigenous elements of food, can alone form Tissues The Non-nitrogenous, or Respiratory elements of food, such as Fat, haA r e not this property ; and Fat and Water in Tissues, are only mechanically absorbed ..... 369 CONTENTS. xiii LETTER XXX. PAGE Respiratory Food Fat, Butter, Sugar of Milk Starch, Cane-sugar, Grape-sugar, &c. Sugar of Milk Its Properties ; oxidisable in presence of Alkalies ; undergoes the Lactic Fermentation in contact with Caseine ; is identical in composition with Grape-sugar Starch ; its Varieties ; convertible into Dextrine and Grape-sugar Table of the Relative Proportions of the Plastic to the Non- nitrogenous Constituents in different Articles of Food Best Pro- portion supplied by Nature in Milk and Grain, or in some kinds of Flesh Popular Mixtures, such as Beans and Bacon, Peas and Pork, Potatoes and Meat, &c., give good Proportions which have been indicated by the instinct Alcohol as a Respiratory Element of Food Relation of Food to Work Performed Rations of Labouring Men, Soldiers, &c. Feeding of Stock ; Fattening The Plastic Matters do not contribute to the Animal Heat Functions of Sugar, &c. Accumulation of Fat : its Origin -from Sugar Table of the Comparative Value of Fat, Starch, Sugar, Alcohol, and Flesh, in regard to the Heat derived from them in the Body Proportion of Nitrogen to Carbon in the Tissues and Excreta . 380 LETTEE XXXI. Essential Importance of the Mineral or Incombustible Elements of Food The Ashes of Vegetable Food are the same as those of Blood and Flesh The Blood invariably Alkaline, and this is a Condition essential to its Fluidity and to all its Functions The Alkaline Salt is the Phosphate of Soda, while in all the Tissues, and in the Juice of Flesh, the Phosphoric Acid is in excess ; but in Her- bivora the Phosphate is partly replaced by another Alkaline Salt, the Carbonate of Soda A knowledge of the Ashes of the Food enables us to predict the precise Salts in the Blood, the Urine, and the solid Excreta The soluble Salts are found in the Urine ; the insoluble, in the Faeces Relations of the Salts of the Blood to the Secretions and Excretions Table of the Urine with Animal Food and with Vegetable Food In Disease, the Analysis of the Ashes of Urine and Blood will become a valuable aid to the Phy- sician The Alkalinity of the Blood essential to the Oxidation of the Respiratory Food, and of the Products of the change of Matter, such as Uric Acid, which, although formed, never reaches the Kidneys in the Herbivora, whose Urine is Alkaline Salts of Vege- table Acids, in the Body, become Carbonates The Excretion of the free Acids in the Urine of Carnivora is essential to preserve the Alkalinity of their Blood The Nature of the Blood and of the Urine may be changed by Diet Iron in the Food, essential to the Blood Functions of Common Salt in the Food and in the Blood Experiments on its use, and suggestions on this Point Endosmosis of Saline Solutions Effects of drinking Spring Water, and Solu- tion of Salt Salt a necessary of Life . . . . . .404 xiv CONTENTS. LETTER XXXII. PAGE Vegetable and Animal Food Composition of Flesh ; itsFibrine, Albu- men, &c. Proper mode of boiling and roasting Meat, and of mak- ing Soup Constituents of watery Extract of Flesh ; Kreatine, Kreatinine, &c. Value of Soup and of Flesh as food Importance of true Extract of Flesh for Hospitals, Armies, &c. Portable Soup of Commerce was chiefly Gelatine, which has no Nutritive value Directions for making pure Extract of Meat Its great value depends on its Inorganic Salts The loss of Nutritive value in Salted Meat depends on the Expulsion of a great part of the juice Different kinds of Meat differ in Nutritive value Veal inferior to Beef, and why Importance of Iron Cheese, Fish, Salted Fish, Eggs, are all deficient in Alkalies and Iron This is probably the reason why they are admitted in fasting Table of the relative proportion of Nitrogen and Carbon in Animal Sub- stances, from Albumen to Urea Chemical relations of Albumen, Fibrine, Caseine, Gelatine, Chondrine, Bile, and Urine Table of the formulae deduced from analyses alone Illustrations of their derivation one from the other Grinding of Grain Flour and Bran Brown Bread of the entire flour preferable to White Bread from bolted flour Rye Bread Adulterations of Bread ; Blue Vitriol ; Alum ; Lime-water should be used instead Baking Yeast prefer- able to Carbonate of Soda and Muriatic Acid Substitutes for Bread in times of scarcity are either merely local or else fallacious. The only true gain would be to save what is thrown away on the Bran, and the Gluten wasted in starch-manufactories Superior digesti- bility of Bread from the entire Meal, or the Pumpernickel of Westphalia The Culinary Art is empirically far advanced Food for different ages Effects of Vegetable and Animal Diet Value of Wine The abuse of Spirits not so much the cause as the effect of poverty Total abstainers eat very much more than wine- drinkers Uses of Tea, Coffee, Chocolate, &c. Theine, or Caffeine, compared to Kreatine and Sugar of Gelatine Mineral elements of Tea, &c. Price of Meat in years of scarcity ; and of Bread Men living on Meat must eat a great deal, and take violent exer- cise Importance of Agriculture compared with Hunting by an Indian Chief Science teaches the economy of force Tendency of riches to inequality of distribution, and thence to universal circulation Money, in the organism of the State, compared to the blood corpuscles in the body, by the circulation of which the change of matter is effected, and life kept up All human actions, as is proved by the statistics of births, deaths, crimes, and justice, are under strict natural laws True science ascertains these laws, and teaches men to observe them 433 LETTER XXXIII. Organic Life in the Ocean The water yields Sea-plants all their ele- ments Function of the Soil in Vegetation ; to furnish the Mineral elements to Plants The Soil is exhausted if the Minerals removed by Crops are not restored by Animal manures, bone, earth, &c. CONTENTS. xv PAGE Causes of the luxuriant growth of Tropical Plants Perennial Plants and Trees require less Mineral food than Annuals Expla- nation of the effects of Drought on the lower leaves of Plants . 485 LETTER XXXIV. Agriculture is both a Science and an Art Its objects Effects of fal- lowing, and of the Mechanical Operations of Agriculture . . . 493 LETTER XXXY. Importance of Alkalies and Silica Natural Silicates in Soils difficult of decomposition In Fallows these are decomposed by the action of the Air Quick-lime effects the same object Effects of burning Clay 498 LETTER XXXVI. Manures Origin of Animal Manures The Excreta contain the salts of the Food ; the soluble are in the Urine, the insoluble in the Dung The same Salts (Phosphates, &c.) from other sources are equally efficacious Theory of Manures The true Problem is to restore to the Soil all we remove from it The Excreta of an Animal fed on any Crop must be the best Manure for that Crop Note on the Author's experience and on Mineral Manures .... 504 APPENDIX. History of the boy with the Golden Tooth Letter of Galileo to Madama Cristina, Granduchessa Madre Crum's soluble Alu- minaCause of Puerperal Fever in the Lying-in-Hospital at Vienna The Flesh of animals tortured to death dangerous as Food Local Causes of Intermittent Fever Reported case of Spon- taneous Combustion ; letters of Re^nault, Pelouze. arid Carlier on the subject New Estimation of the Quantity of Blood in Man by Bischoff Estimation of the Food consumed by working miners at the elevated mines at Gastein and Kauris A new SOUD for Invalids A method for improving the quality of Bread To bake bread from Sprouted Grain Legends of the BJainegau .... 515 INDEX . .531 . LETTEES ON CHEMISTRY, LETTER I. Importance of Chemistry Its rank among sciences Recent origin of modern Chemistry Like Mathematics and Physics, Chemistry is a language, an instrument, which can only lead to discovery in the hands of genius Chemical analysis Applied Chemistry Theory of Chemistry Chemical processes and analysis are the foundation of all the rest of the science Chemistry essential to the future progress of Medicine, Geology and Physiology Philosophical method of research into the vital phenomena Great advantages already derived from Chemistry. CHEMISTRY is so often alluded to in modem writings, that it may perhaps be regarded as a problem of some importance to indicate more specially the influence of this science on the useful arts and on industry, as well as its relations to agri- culture, physiology, and medicine. I would desire, in the first section, to establish the con- viction, that Chemistry, as an independent science, offers one of the most powerful means towards the attainment of a higher mental cultivation ; that the study of Chemistry is profitable, not only inasmuch as it promotes the material interests of mankind, but also because it furnishes us with insight into those wonders of creation which immediately surround us, and with which our existence, life, and develop- ment, are most closely connected. It is so congenial to the human mind to inquire into the causes of natural phenomena, the sources of the life of plants 2 LETTERS ON CHEMISTRY. and animals, the origin of their nutrition, the conditions of their healthy structure, the transformations passing in the world around us and of which we form a part, that those sciences which give satisfactory answers to our inquiries, exercise more influence than any others on the progress of mental cultivation. The study of the natural sciences, as a means of education, is a necessity of our age. Along with the all-important instructions in the fundamental principles of morality and religion, education should unfold and exercise the different mental faculties, and store the mind with a certain amount of general useful knowledge. JSTo science like Chemistry offers to man such a multitude of subjects for thought and reflection, and such stores of knowledge imbued with the charms of never-ending fresh- ness; none is more calculated to awaken the talent for observation, or to sharpen the intellect in the strict method of applying proof for the establishment of a truth, or in the inquiry into the cause and effect of a phenomenon. As the human mind advances in knowledge, from whatever source that knowledge may be derived, all its powers are strengthened and elevated. The acquisition of a new truth is equivalent to a new sense, enabling us now to perceive and recognise innumerable phenomena which remain invisible or concealed to others, as they formerly were to ourselves. Chemistry leads man into the domain of those latent forces, whose power controls the whole material world, and on whose operation is dependent the production of the most important necessaries of life and of society. As a part of the science of Natural Philosophy, it is most intimately connected with physics : and this latter science is closelj' related to astronomy and to mathematics. The simple observation of nature forms the foundation of every branch of natural science, and only very gradually has experience assumed the form of science. Thus the change of position of the stars, the succession of day and night, and the variations of the seasons, gave birth to astronomy. With astronomy arose physics, and at a certain stage of its SCIENCE FOUNDED ON EXPERIENCE 3 development, it gave birth to scientific chemistry. From organic chemistry, the laws of life, the science of physiology will be developed. Experience is the source of all science. The duration of the year was at first determined, the changes of the seasons explained, and eclipses of the moon calculated, without any acquaintance with the laws of gravitation ; mills were built, and pumps constructed, without the knowledge of atmo- spheric pressure ; glass and porcelain were maimfactured, stuffs dyed, and metals separated from their ores by mere empirical processes of art, and without the guidance of correct scientific principles. Even geometry had its founda- tion laid in experiments and observations ; most of its theorems had been seen in practical examples, before the science was established by abstract reasoning. Thus, that the square of the hypothenuse of a right-angled triangle is equal to the sum of the squares of the other two sides, was an experimental discovery, else why did the discoverer sacrifice a hecatomb when he made out its demoiistration. How different now is the aspect of the discoveries of the natural philosopher, since the inspiration of a true philosophy has led him to investigate phenomena, in order to draw conclusions as to their causes and the laws which regulate them. From one sublime genius from Newton more light has proceeded than the labour of a thousand years preceding had been able to produce. The true theory of the movements of the heavenly orbs, and of falling bodies, has become the parent of innumerable other discoveries. Navi- gation, commerce, industry, nay, every individual of our species, has derived, and will continue to derive, from his discoveries, as long as mankind exists, incalculable benefits, both intellectual and material. Without an acquaintance with the history of physics, it is impossible to form any correct opinion of the effect which the study of nature has exercised upon the cultivation of the mind. In our schools mere children are now taught truths, the attainment of which has cost immense labour and indescribable efforts. They smile when we tell them -that B 2 4 LETTERS ON CHEMISTRY. an Italian philosopher wrote an elaborate treatise to prove that the snow found upon Mount ^Etna consists of the same substance as the snow upon the Alps of Switzerland, and that he heaped proof upon proof that both these snows, when melted, yielded water possessed of the same properties. And yet this conclusion was really not so very palpable, since the temperature of the two climates so widely differ, and no one in those days had any notion of the diffusion of heat over the surface of the earth. When a schoolboy takes a glassful of liquid, and, placing a loose piece of paper over it, inverts the glass without spilling a drop of its contents, he only astonishes another child by his performance, and yet this is the identical experiment which renders the name of Torricelli immortal. It is a variation of that experiment with which the burgomaster of Magdeburg (Otto von Guericke) threw the Emperor and the princes of the empire at Ratisbon into speechless astonishment. Our children have more correct notions of nature and natural phenomena than had Plato ! they may treat with ridicule the errors which Pliny has committed in his Natural History ! By the study of history, of philosophy, and of the classics, we obtain a knowledge of the intellectual world, the laws of thought, of mental inquiry, and of the spiritual nature of man. Whilst we hold communion with the spirits of the great and good of all ages, we derive from the experience of past centuries the power of soothing and governing the passions, and of softening the heart : we are enabled to comprehend man as he exists at the present time, since his moral nature remains ever the same. We are taught to embellish, and present, in the most engaging form, the prin- ciples of truth, of justice, and of religion, and thus to make the most enduring impression upon the minds of others. History and philosophy, however, could not prevent men from burning their fellow-creatures for witchcraft. For when the great Kepler went to Tubingen to save his mother from the stake, he succeeded only by proving that she possessed none of the characteristic signs essential to a witch ! FOUNDATION OF MODERN CHEMISTRY. 5 Only about seventy years ago was chemistry, like a grain of seed from a ripe fruit, separated from the other physical sciences. With Black, Cavendish, and Priestley, its new era began. Medicine, pharmacy, and the useful arts, had pre- pared the soil upon which this seed was to germinate and to nourish. The foundation of the science is, as is well known, an apparently very simple theory of the phenomena of com- bustion. We have now experienced the great benefits and blessings which have sprung and been diffused from this view. Since the discovery of oxygen the civilised world has undergone a revolution in manners and customs. The knowledge of the composition of the atmosphere, of the solid crust of the earth, of water, and of their influence upon the life of plants and animals, was linked with that discovery. The successful pursuit of innumerable trades and manufactures, the profitable separation of metals from their ores, also stand in the closest connection therewith. It may well be said, that the material prosperity of empires has increased many-fold since the time oxygen became known, and the fortune of every individual has been aug- mented in proportion. Every discovery in chemistry has a tendency to bring forth similar fruits. Every application of its laws is capable of producing advantages to the state in some way or other, augmenting its powers, or promoting its welfare. In many respects chemistry is analogous to mathematics. On the one hand, this latter science teaches us to measure land, to erect buildings, and to raise weights, and is thus, like arithmetic, an instrument, the skilful employment of which secures most obvious and universal advantages : on the other hand, mathematics enable us to draw correct logical conclusions according to definite rules; teach us a peculiar language, which allows us to express a series of such conclusions in the most simple manner, by lines and symbols intelligible to every one who knows this language ; give us the power to deduce truths by means of certain operations with these lines and symbols ; and furnish us with an insight into relations of things formerly obscure or unknown to us. 6 LETTERS ON CHEMISTRY. The mechanician, the natural philosopher, the astronomer, employ mathematics as an indispensable instrument for the attainment of their ends. They must, indeed, be so prac- tised in its management that its application becomes a mechanical habit, requiring only the exercise of memory. But it is not the mere instrument which plans and executes the work, but the human intellect. It is obvious, that without the power of observation, without sagacity and judgment, all mathematical knowledge is useless. We may imagine a man who, favoured by a good memory, has rendered himself intimately acquainted with every theorem of mathematics, who has obtained an eminent degree of skilfulness in handling this instrument, but who is altogether unable to propound a problem for solution. If we propose to him a problem, and give him the conditions for the solution of a question, he will succeed in obtaining an answer by performing the current operations with which he is familiar, and express it in a formula consisting of certain symbols, the meaning of which, however, is perfectly unin- telligible to him, because he is deficient in other attainments essential for judging of its truth. Such a man is a mere calculating machine. But so soon as he possesses the capacity and the talent to propose a question to himself, and to test the truth of his calculations by experiment, he becomes qualified to investigate nature. For, from whence should he derive his problems, if not from nature or from life ? He is denominated a mechanician, an astronomer, or a natural philosopher, if, starting from observation, he is able fo ascertain the connection of certain phenomena and the causes producing them ; and then is capable, not merely of expressing the results in a formula, in the language of the mathematician, but of making an application thereof, re- producing his formula in the shape of a phenomenon or external fact, thereby testing its truth. The astronomer, the mechanician, the natural philosopher, therefore, in addition to mathematics, which they use only as an instru- ment, must possess the art of observing and interpreting phenomena, and the ability to present the results of abstract MATHEMATICS AN INSTRUMENT. 7 reasoning in a visible shape by means of a machine or some form of apparatus ; in fact, to prove the correctness of their conclusions by experiment. The natural philosopher pro- poses to himself the solution of a problem, he endeavours to ascertain the causes of a given phenomenon, the variations it undergoes, and the conditions under which these changes take place. If his questions have been correctly put, and all the circumstances (the factors) taken into account, he succeeds in obtaining, by the aid of mathematical processes, a simple expression for the unknown quantity or relation which has been the object of his search. This expression or formula, translated into ordinary language, explains the mutual connection of the observed phenomena, or of the experiments which he has instituted; and the formula is correct when it enables him to produce a certain series of new phenomena which are deductions from it. It is easy to perceive how the mathematics stand con- nected with the study of nature ; and that, besides mathematics, a high degree of imagination, acuteness, and talent for observation, are required to make useful dis- coveries in astronomjr and other physical sciences. It is a vulgar fallacy to ascribe discoveries to mathematics. It happens here, as in a thousand other cases, that the effect is opnfounded with the cause. Thus, effects are often ascribed to the steam-engine, which are properly due to fire, to coals, or to the human intellect. In order to make discoveries in mathematics, the same mental vigour, the same acuteness, the same power of thought are necessary' as are essential to the solution of other difficult problems. Such discoveries in mathematics are the successive steps towards the perfection of the instrument, by which it is rendered capable of innu- merable useful applications, but the instrument alone makes no discoveries in natural science. It makes use of data furnished to it, of facts observed by the senses, and of ideas created by the mind. Experimental natural philosophy stands in this sense in contrast with mathematical natural philosophy. It is the former which discovers, examines, and prepares facts for the mathematician. The task of experi- 8 LETTERS ON CHEMISTRY. mental physics is to express the laws, the general truths deduced, in the form of phenomena, to illustrate the mathe- matical formulae by experiments, to make them manifest to the senses. Chemistry, in answering her own questions, proceeds in the same manner as experimental physics. She teaches the methods of discovering and determining the qualities of the various substances of which the crust of the earth is com- posed, and which form the constituents of animal and vegetable organisms. We study the properties of bodies, and the alterations they undergo in contact with others. All oui- observations, taken collectively, form a language. Every property, every alteration which we perceive in bodies, is a word in that language. Certain definite relations are manifested in the deportment of bodies toward each other; we observe a similarity of form, or analogy of properties, or diversities in both respects. Such diversities are as numerous and various as the words of the most copious language, and they are no less varied in their signification and in the relations which they bear to our senses. The name of each of these bodies possesses a peculiar meaning to the chemist. The words sulphur, iodine, iron, are to him not only signs of similarity and dissimilarity in external qualities, colour, form, hardness, &c., but they represent a series of latent properties, which are called into play only when in contact with other bodies. Bodies, like men, possess certain external properties, as well as a number of others which are concealed from view. By their external corporeal properties we recognise indivi- duals, and distinguish them from each other; but we are not in a position to ascertain by the senses, or by the external corporeal properties, those hidden qualities, such as gentle- ness or impetuosity, generosity or avarice, which characterise an individual ; because these are only brought out by inter- course with man. In the same way, the term atmospheric air conveys to the mind of the chemist the idea of a number of properties. No mortal eye has ever seen a particle of air ; for sight presupposes a certain effect produced on the eye, CHEMISTRY A LANGUAGE. which particles of air are quite incapable of producing. They possess, however, other properties which chemistry brings to view, and by which the chemist not only ascertains their presence when they escape the notice of others, but he is also enabled by them to show that this invisible impalpable material consists of several other equally invisible substances. By his exact knowledge of their properties, he can separate them from each other, weigh them, and make their presence manifest to others. He is able to show that the air which bums in our street lamps, consists of five or six totally dif- ferent airs. He points out in a constituent of atmospheric air, employed in respiration, one of the most indispensable requisites for animal life ; and in a product of respiration, one equally important to vegetable life. He exhibits the intimate connection between the visible and invisible material \vorld, of the existence of which our ancestors had 110 idea. He is enabled to do all this by his knowledge of the peculiar properties of these bodies, acquired by means of visible phenomena, or such as can be recognised by the senses. He must first bring these substances in contact with others to render these phenomena manifest ; but when he has done this, they then become more distinct than the tones of a chord when struck, and as intelligible as the black lines and characters which convey to a far distant friend our invisible thoughts. Bodies differ in quality ; the meaning conveyed to us by their properties, to pursue the illustration, changes ac- cording to the mode in which these elements are arranged. As in all other languages, so we have in that peculiar language in which material bodies hold converse with us, articles, substantives, and verbs, with their variations of cases, declensions, and conjugations. We have also many syno- nymes ; the same quantities of the same elements produce a poison, a remedy, or an aliment, a volatile or a fixed body, according to their manner of arrangement. We know the signification of the properties of bodies, that is, of the words in which natiu-e speaks to us, and we use the alphabet to decipher and to read them ; as, for instance, a 10 LETTERS ON CHEMISTRY. fountain of mineral water in Savoy cures that remarkable enlargement of the thyroid gland denominated goitre, I put certain questions to that water, the combination of the several letters in its answers informs me that it contains iodine. A man, having partaken of some food, dies soon after, with all the symptoms of poisoning. The language of phenomena, with which the chemist is familiar, tells him that arsenic, or corrosive sublimate, or some other body, was the cause of death. The chemist, by his questions, compels a mineral to speak, to disclose its composition ; it tells him that it contains sulphur, iron, chromium, silica, alumina, or any other word of the chemical language of phenomena, arranged in a certain order. This is CHEMICAL ANALYSIS. Then, again, the language of phenomena leads the chemist to new combinations, from which he derives innumerable useful truths that are applicable to the improvement of manufactures and arts, to the preparation of remedies, and to metallurgy. He has succeeded in deciphering the word ultra- marine. The next step is to construct this word in a tangible form, to reproduce ultramarine with all its properties. A knowledge of the composition of bodies enables chemists to solve questions, which a few years ago were supposed to be beyond their powers. The discoveiy of the composition of soils and of the ashes of plants, enables them to see the reason why one and the same plant, grown without manure on the same soil for three, another for seven, ten, or more years, at length cease to flourish on it ; why one field pro- duces wheat, but not beans ; barley, but not tobacco ; and why from another a rich crop of turnips, but no clover is obtained. Chemistry explains the operation of manures, and teaches the mode of restoring fertility to an exhausted soil. This is APPLIED CHEMISTRY. In what degree the form of an organic substance is de- pendent on its constituent elements is the most important physiological problem for chemistry to solve. It has to show what transformation takes place in food in its conversion into blood, and what changes the elements of the blood CHEMICAL THEORY. 11 undergo in becoming fixed constituents of organs. The nutritious property of an article of food, the action of a medicine, or of a poison, all these qualities are attached to certain material elements, in which reside their virtues. The vital properties of an organ or animal fluid are dependent on its composition and an alteration in this composition is the consequence of every action of disease. The restoration of the original composition is the object proposed in the application of remedies, and the action of the latter is determined by their composition. Chemistry can propose to itself no weightier problem to solve than the discovery of the connection existing between the medicinal or poisonous action of a substance and its elementary constitution. The inquirer has still in the organic frame much of the unknown before him, but, judging from recent discoveries, nothing which can be called incomprehensible. Hitherto scarcely any demand has been made upon the science of chemistry, by arts, manufactures, or physiology, which has not been responded to. Every question, clearly and definitely put, has been satisfactorily answered. Only when the inquirer had no precise idea of the problem to be solved has he remained unsatisfied. The last and most elevated object of chemistry is the investigation of the causes of natural phenomena, of their variations, and of those factors w T hich are common to different series of phenomena, The chemist ascertains the laws which regulate natural phenomena, and by combining together all that is observable and has been observed by the senses, he at last attains to a general intellectual expression for the phenomena, in other words, to a THEORY. But to enable us to read the book of nature, to understand its language, to perceive the truth of the theories of the philosopher, to subject to our will and examine at our pleasure the phenomena upon which a theory is based, and the powers producing them, we must necessarily learn the alphabet of the language, we must become familiar with the use of the signs or symbols employed, and by practice acquire skill in their management, and a knowledge of the laws which 12 LETTERS OX CHEMISTRY. regulate their combinations. As in the higher branches of physics it is indispensable that the philosopher should have attained considerable practical skill in mathematical analysis, so the chemist, before he can investigate natural truths suc- cessfully, must have the most perfect knowledge of chemical analysis he must be able to express all his conclusions all his results in the form of phenomena. Every experiment is a thought thus rendered perceptible to the senses. In order to prove or disprove our conclusions, we have recourse to experiments, to the interpretation of phenomena at will. There was a time when chemistry, in common with astro- nomy and all the physical sciences, was nothing more than an art, founded on empirical practice, subject only to rules discovered by experience; but since the causes of the changes in bodies which it effects, and their laws, i. e. the reasons of its rules, have become known, the empiric art has lost its value and importance. The acquisition of skill in manipulation by laborious and long-continued application, the tedious methods and endless precautionary measures formerly necessary to success in chemical manufactures, have become wholly needless since a correct knowledge of causes has been obtained. The strange apparatus and utensils of the chemist of former ages, their stoves and stills, are now mere matters of curiosity. The success of an experiment, or of a process, depends far less upon mechanical skill, than upon knowledge. Failure is the result of ignorance, and discoveries are made, not by manual dexterity, but by skill in combination, and by that intellectual power which creates new thoughts. In our lecture-rooms we teach the letters of the alphabet ; in our laboratory their use. It is in the latter that the student acquires a readiness in reading the language of phenomena, that opportunities are fumished to him of learning the rules of combinations, and of gaining a ready dexterity in their application. As soon as these signs, letters, and words have become formed into an intellectual language, there is no longer any danger of their being lost, or oblite- CHEMISTRY APPLIED TO PHYSIOLOGY. 13 rated from his mind. With a knowledge of this language he may explore unknown regions, gather information, and make discoveries wherever its signs are current. It enables him to understand the manners, customs, and wants pre- vailing in those regions. He may, indeed, without this knowledge, cross the frontiers of the known, and pass into the unknown territory ; but he exposes himself to innu- merable misunderstandings and errors. He asks for bread, and he receives a stone. Medicine, Physiology, Geology, and Experimental Physics are the unexplored regions, the forms of government, laws, and institutions of which the philosopher is desirous of learning. Without a knowledge of the language of pheno- mena, and the art of interpreting it, there is nothing for him to discover but mere forms and external qualities. The significant and mighty movement in physiology of a recent date is directed to remove the existing deficiency, and to facilitate the introduction of chemistry into this depart- ment. The mere knowledge of external forms and physical properties no longer satisfies physiologists ; they are deeply impressed with the importance, nay, the indispensable neces- sity, of a more profound, more intimate, more chemical in- sight into the composition and changes of organic bodies. But is such an insight possible without the knowledge of the chemical language ? If other and less gifted physiologists reproach chemistry with making discoveries which are useless and inapplicable to their science, we may rest assured, that they understand neither the meaning nor value of chemistry. They can no more read its language than they could a work written in Hebrew characters without having previously learned those characters. It is not unworthy of remark, that many physicians pro- fess to hold physiology in contempt, exactly as they do chemistry ; that medicine reproaches physiology, and with equal injustice, as she reproaches chemistry. There are, in fact, many physicians and medical writers who assert the impossibility of elevating dietetic and medical 14 LETTERS ON" CHEMISTRY. practice to an exact science ; and upon this assumption they proceed to explain, in their own way, the essential conditions of " life." They strive to force upon us as natural laws, and as laws of health and of disease, their own imperfect views of physiological, pathological, and therapeutic phenomena. In their opinion, it is not the study of nature, but of their books, which is valuable to medical practice. They have always at command, in the terms "vital force," "vital power," wonderful causes, by which they explain all pheno- mena they do not understand ; thus attempting to elucidate what is unknown to them, by a certain something, utterly incomprehensible and indefinable. In each disease, they see in action an inherent independent force, opposed to the physiological. As they have no hope of ever arriving at an exact knowledge of the processes of health, disease, and restoration, they regard dietetics and therapeutics as con- sisting chiefly of a knowledge of what is useful or hurtful, under certain similar circumstances. The natural sciences, together with physiology, chemistry, and anatomy, serve at most only to furnish signs by which to j ndge whether these circumstances are similar or dissimilar. These sciences merit observation, only so far as they can be used in establishing their views of similarity or dissimilarity in the phenomena of disease, or in ascertaining the value or harm of medicinal action. Rejecting altogether an exact acquaintance with nature, the source of all knowledge, they look upon them- selves as the true dispensers of light and information ; and the most modest opposition to the views of such infallible guides is regarded by them as downright heresy. Persons unacquainted with the present position of science, and misled by the views just stated, would easily suppose that the natural sciences, physiology, and chemistry, had for centuries arrived at their full development, that the natural forces had been investigated, and their laws determined, and that every effort had already been made, and always in the proper direction, to gain an insight into the vital processes. Had this been the case, a reasonable person might probably have given expression to the opinion, that such an insight VITAL PROCESSES REGULATED BY LAWS. 15 was not to be expected, without thereby implying any " impossibility " in its future accomplishment. Now, so far from physiological and chemical inquiries having been pursued for centuries in connection with therapeutics and dietetics, they are now but in their infancy. Though scarcely com- menced, they have already established the conviction, that both have a scientific basis resting on exact physiological knowledge ; and that the processes of the living body are regulated by natural laws, which are proved by daily disco- veries to be within the scope of observation. The truth is, that there existed for centuries excellent physicians who knew nothing of anatomy ; and diseases have been treated with success, during the same period, without any real knowledge of their nature, just as at the present day we are unacquainted with the real nature of "fever," or " inflammation." But there is now no ground for concluding that a correct insight into their nature is impossible. The physician who has learned medicine, not as a science, but as an empirical art, acknowledges no principles, but only rules derived from experience. The object of his inquiries is only whether a remedy, in any given case, had a good or a bad effect. This is all the empiric cares about. He never asks why ? He never inquires into the causes of what he observes ! From what a different point of view should we contemplate the abnormal or diseased conditions of the human body, if we were first thoroughly acquainted with its normal con- ditions ; how differently would the treatment of diseases be conducted if we had perfectly clear notions of the processes of digestion, assimilation, and excretion ! Without just views of force, cause, and effect without a clear insight into the very essence of natural phenomena without a solid physiological and chemical education, is it to be wondered at that men, in other respects rational, should defend the most absurd notions ; that the doctrines of C Halmejiiann should prevail in Germany and find disciples in | all countries ? Reason alone will not prevent whole nations S from falling into the most abject superstitions, whilst even 16 LETTERS ON CHEMISTRY. a child whose mind has been duly developed and instructed will repudiate the fear of ghosts and hobgoblins. Can men who do not apprehend the nature of scientific investigation in a philosophical spirit, and who cannot interpret the language of phenomena, can such men be expected to derive the least advantage from the discoveries of chemistry or physiology ; and can they be deemed capable of making the most insignificant application to practical purposes of those discoveries ? We often see such persons annoyed that truth should be so simple, and yet, in despite of all their efforts, they cannot succeed in deriving from it any practical advantages. To ascertain the nature of the vital force and to understand its operation, a course must be taken by physicians, similar to that which has been so successfully followed in physics and chemistry. There was certainty, at one time, no state of matter more obscure, more completely hidden from the corporeal and intellectual eye of man, than that which we denominate electricity. A thousand years elapsed from the birth of natural philosophy ere the human mind had obtained the slightest notion of the existence of this, the most stupendous power in nature, a power performing the most important part in all the alterations of inorganic matter, and all the processes of vegetable and animal life. The philosopher, undeterred by innumerable difficulties, has at length obtained as the reward of his untiring researches, a most intimate knowledge of electricity, and has made it his handmaid. He knows now that electricity, heat, light, and magnetism had a common origin. By means of electricity he has subjected the sister sciences to his service. By its aid he sends, with the speed of lightning, his thoughts to the most distant regions, extracts the noblest metals from the poorest ores. It was by electricity that he first arrived at a knowledge of the true nature of the constituents of the earth. By its means he sets ships in motion and multiplies objects of art. When a power of nature, invisible and impalpable, is tjie subject of scientific inquiry, it is necessary, if we would comprehend its essence and properties, to study its rnani- PHILOSOPHICAL METHOD OF RESEARCH. 17 festations and effects. For this purpose simple observation is insufficient, since error always lies on the surface, whilst truth must be sought in deeper regions. If we apprehend a phenomenon or observed fact erro- neously, or if we entertain an incorrect conception of its connections and relations, we are said to commit an error. Our only protection against this is to test the truth or false- hood of our notions by producing the phenomenon ourselves, under varied circumstances, and by ascertaining the con- ditions of its first appearance, vazying these conditions, and closely observing the influence of these alterations. In this manner our first observation is corrected and rendered clear to our minds. Nothing must be left to the fancy or imagination. The true philosopher always seeks to explain and illustrate nature by means of facts, of phenomena ; that is, by experiments, the devising and discovery of which is his task, and by which he causes the object of his investigation to speak, as it were, intelligibly to him. No single isolated phenomenon, taken by itself, can furnish us with its own explanation ; but it is by carefully observing and arranging all such facts as are in connection with it, that insight into its nature is attained. For we must never forget that every phenomenon has its reason, every effect its cause. BACON. Such opinions as, that the creative energy of nature produces the most various kinds of plants, and even animals, out of decayed rocks or putrid vegetable matter, without seeds or sperm ; that nature abhors a vacuum ; that iron and phosphorus are formed, from other elements, in the living body of animals, and the like, are emanations of ignorance and indolence, and display men's incapacity to discover the true origin 'and causes of things. But a thousand uncon- nected observations have no more value, as a demonstrative proof, than a single one. If we do not succeed in discovering causes by our researches, we have no right to create them by the imagination. Thus, when we have learned that infusorial animalcules are propagated by eggs, it only remains for us to 18 LETTERS 0^ CHEMISTRY. inquire how the eggs are conveyed to where we find them. For the moment the imagination alone is taken for a guide, and is allowed to solve questions left undecided by researches, investigation ceases, truth remains unascertained, and there is not only this negative evil, but in error we create a MONSTER, envious, malignant, and obstinate, which, when at length truth endeavours to make its way, crosses its path, combats, and strives to annihilate it ! Thus it was in the time of Galileo ; and thus it is still, everywhere, in every science, where mere opinions are allowed to have the force of proofs. If we confess the incompleteness of our knowledge, and simply admit our inability to answer the questions which arise as we contemplate the phenomena of nature, those questions remain as problems for futurity to solve, and excite the attention and exertions of thousands ; zeal is kindled and kept alive, and in process of time their solution will certainly be accomplished. An explanation satisfies the mind ; and if the explanation include error which is regarded as truth, this arrests the activity of the mind, as well as the progress of truth itself. The imagination, in thousands of cases, gives rise to thousands of errors, and nothing is more hurtful to the progress of natural science nothing has more power in limiting and distorting our views of natural pheno- mena, than an old established error. It is infinitely difficult to refute a false doctrine, precisely because it rests on the conviction that that is true which is really false. It is certainly not conformable to a rational philosophy of nature to attempt an explanation of the processes of forma- tion, nutrition, and secretion in the animal body, before we have obtained a correct knowledge of alimentary substances, and the sources whence they originate, and before albumen, caseine, blood, bile, cerebral substance, &c., had been subjected to a searching investigation." Before these substances have been successfully analysed, they are mere names, the letters composing which, at the utmost, we know, but whose sig- nification is unknown. How can it be expected that any , useful information should be derived from the mere terms, CHEMICAL AND VITAL FORCES. 19 until the properties and relations of the substances them- selves are known ; until we have studied the metamorphoses they undergo when in contact with other bodies ; until, hi short, we have forced them to speak in answer to our questions ? The cause of the phenomena of life is a force, which does not act at sensible distances ; its activity becomes manifest only when the aliments or the blood come into immediate contact with the organ destined for their reception or altera- tion. The chemical force manifests itself precisely in the same manner; indeed there are no causes in nature pro- ducing motion or change in bodies no powers more closely allied to each other than the chemical and vital forces. We know that wherever different substances are brought into con- tact with each other, chemical actions take place. To sup- pose that one of the most energetic powers of nature should take no part in the processes of the animal organism, although here all the conditions under which it commonly manifests its activity are united, would be against every established rule for the proper study of nature. But so far from there being any foundation for the opinion that chemical force is subordinate to the vital power, so as to become inope- rative or imperceptible to- us, the chemical effects of oxy- gen, in the process of respiration (for example), are seen in full activity during every second of life. Moreover, urea, allantoine the acid which is found in ants and tvater-beetles, namely formic acid, oxalic acid, the oils of valerian root, of the Spircea ulmaria, of the Gualtheria, procumbens, are products of the vital process, &c. ; but is their production, we must ask, attributable to the vital force 1 We are able to produce all these compounds by chemical processes, that is, by the chemical force. The chemist pro- duces the crystalline substance found in the fluid of the allantois of the cow, from the excrements of snakes and birds : he makes urea from charred blood ; sugar, formic acid, and oxalic acid from saw-dust ; the volatile oil of Spircea iilmaria-, of GuaUkeria procumbent, from willow-bark ; the volatile oil of valerian from potatoes. These results are c 2 20 LETTERS ON CHEMISTEY. enough to justify us in entertaining the hope that we shall, ere long, succeed in producing quinine and morphine-, and those combinations of elements of which albumen and jibrine, or muscular fibre, consist, with all their characteristic properties. Let us, however, carefully distinguish those effects which belong to the chemical, from those which depend peculiarly upon the vital force, and we shall then be in the right channel for obtaining an insight into the latter. Chemical action w r ill never be able to produce an eye, a hair, or a leaf. But we know, with absolute certainty, that the formation of hydrocyanic acid and of the oil of bitter almonds, in those seeds, of oil of mustard and of sinapine in mustard, and of sugar in germinating seeds j that all these are the results of chemical decompositions. We see that the stomach of a calf, when dead, with the addition of some hydrochloric acid, acts upon flesh, and upon coagulated albumen, precisely in the same manner as the living stomach acts ; that is, these substances become soluble, and are, in fact, digested. All this justifies us in inferring, that by the scientific investiga- tion of nature, we shall arrive at a clear comprehension of the metamorphoses which alimentary substances undergo in the living organism, and obtain an insight into the action of remedies. Without a profound study of chemistry and natural philosophy, physiology and medicine will obtain no light to guide them in the solution of their most important problems, that is, in the investigation of the laws of life, and the removal of abnormal states of the organism. Without a knowledge of chemical forces, the nature of the vital force cannot be fathomed ; the scientific physician can expect to derive assistance from chemistry only when he shall have qualified himself to put his questions to the chemist correctly. Commerce and the arts have already derived immeasurable advantages from the progress of chemistry ; mineralogy has become a new science since regard has been had to the com- position of minerals and the chemical relations of their con- GREAT VALUE OF CHEMISTRY. 21 stituents. If the composition and chemical nature of rocks and strata be not in like manner investigated, and to a greater extent than has been hitherto done, it will be impos- sible to effect any considerable progress in geology. Che- mistry, moreover, is the foundation of agriculture, and we cannot hope to give a scientific form and basis to this important art without a knowledge of the constituents of the soil, and of the substances which constitute the food of plants. Without an acquaintance with chemistry, the statesman must remain a stranger to the true vital interests of the state, to the means of its organic development and improve- ment ; his attention cannot become sufficiently alive, nor his perception adequately acute, in regard to what is really useful or injurious to his country, to society. The highest eco- nomic or material interests of a country, the increased and more profitable production of food for man and animals, as well as the preservation and restoration of health, are most closely linked with the advancement and diffusion of the natural sciences, especially of chemistry. Without the knowledge of natural phenomena, and of the laws by which they are regulated, the human mind is incap- able of forming an adequate conception of the greatness and unfathomable wisdom of the CREATOR; for all the images which the most inexhaustible fancy or the most culti- vated intellect can form will appear, when compared with the reality, but as glittering, variegated, unsubstantial bubbles ! The great desideratum of the present age is practically manifested in the establishment of schools in which the natural sciences occupy the most prominent place in the course of instruction. From these schools a more vigorous generation will come forth, powerful in understanding, qualified to appreciate and to accomplish all that is truly great, and to bring forth fruits of universal usefulness. Through them the resources, the wealth, and the strength of empires will be incalculably aug- mented ; and when, by the increase of knowledge, the weight 22 LETTERS ON CHEMISTRY. which presses on human existence has been lightened, and man is no longer overwhelmed by the pressure of earthly cares and troubles, then, and not till then, will his intellect, purified and refined, be able to rise to higher and higher objects. INDUCTIVE AND ARISTOTELIAN PHILOSOPHY. 23 c LETTER II. The Inductive and Aristotelian pliilosophy compared The true mode of investigating nature, and of explaining natural phenomena Observation and reflection necessary to success The art of observing requires practice and training Value of experiments to ascertain natural laws Theory and practice contrasted Problems proposed to be solved by Chemistry Philosophical relations of Chemistry Immensity of the universe Mind the cause of motion Importance of the study of natural laws, such as those of Chemical Combination. IF a natural philosopher has succeeded in enriching social life by his inquiries, the history of science shows that all his results were based on a method of investigation which, we may assert, has influenced and called forth the extra- ordinary progress of the last fifty years in manufactures, the industrial arts, mechanics, and in the natural sciences. To Francis Bacon and Galileo we are indebted for a know- ledge of this method of inquiry, banished by a false philo- sophy for centuries from medicine and the natural sciences, but which now makes daily conquests in the interests of mankind. We look back on German natural philosophy as on a dead tree, which bore the finest leaves and most beautiful flowers, but no fruit. With an infinite expendi- ture of mind and sagacity, pictures only were created ; but as Goethe has well expressed it in his " Science of Colours,'' the most brilliant colours are after all but dim light. We strive to attain to a pure light, and that is truth. For centuries, the explanation of natural phenomena has been a subject of deep interest, but the views we now hold have nothing in common with those of the philosophic schools, from the time of Aristotle onwards. According to Aristotle, gravity is the cause of the falling of bodies. Gravity is that inherent property in bodies which gives them a tendency to a downward motion i.e., to 24 LETTERS ON CHEMISTRY. fall. A stone falls because it is heavy i.e., because it has a tendency to a downward motion i.e., because it falls. Opium causes sleep, because it is a body possessed of soporific qualities i.e., because it causes sleep. The caustic properties of calcined lime depend on the presence of a body called causticum. The sour taste of a substance is due to the presence of the universal acid principle. To every effect a term was applied ; this term was called the cause, and it served as the explanation of the effect. A certain something gave to gold its colour and unchangeableness ; quicksilver was attempted to be converted into silver by the withdrawal of a certain something to which its fluidity was due ; a certain something caused hardness in bodies, or gave to them their peculiar odour ; and the presence of a certain something (phlogiston) communicated combustibility to bodies. By ascribing so many hidden qualities or things to the numberless effects observed on all sides, a limit was set to the investigation of the cause of each everything was known to which these terms were applied. A word played the part of an explanation, and the place of truth was assumed by a blind belief by an unthinking repetition of unproved opinions. We indeed require understanding and experience to accept as truths many occurrences which have not befallen our- selves, and facts discovered by others but never observed by ourselves. We believe in the events, circumstances, and facts which are asserted by trustworthy persons, if they are not opposed to the laws of nature, or if their effects have been in any way or at any time observed by us or by other trustworthy persons. W"e believe in the existence of Julius Csesar, whom we have never seen, not only because he was seen by his contemporaries, but because his existence is established by occurrences, manifested by their effects, cen- turies after, in the history of mankind. We do not believe in ghosts, though thousands are said to have seen them, because the laws of light teach us that even a material body of a certain degree of fineness, as atmospheric air, for TRUE MODE OF RESEARCH. 25 A example, cannot be seen, and because an unsubstantial being / j no longer possesses the property of reflecting light, which is j essential to its becoming visible. The species of faith, or ' credulity, which leads to the belief in ghosts, belongs not to science ; it is the worst enemy of knowledge ; for by knowledge it is at once destroyed. \ The explanations of phenomena given by natural philo- sophers of our day are widely different from those of former times. The present race of inquirers pay no attention whatever to the most subtle creations of the mind; they regard as their object only that species of knowledge which is acquired by unwearied perseverance and labour. When a philosopher of our day wishes to explain a phenomenon such as the burning of a candle, the growth of a plant, the freezing of water, the bleaching of a colour, the rusting of iron, he puts the question not to himself not to his own mind but to the phenomenon to the fact itself. He asks what-ckenmstance precedes, what follows this phenomenon ? The former he calls the cause or condition of the pheno- menon, the latter is designated the effect. The growth of a plant presupposes the existence of a seed, a germ, and a soil, and the necessary action of the atmosphere and moisture. But soil and atmosphere are not in themselves conditions, for there are lime, clay, and sandy soils, which quite differ from each other in their composition and qualities. The word soil is a collective term for a number of conditions which are present in the proper rela- tions in fertile soils for the growth of plants, but in the sterile some or all are wanting. To produce the effect i.e., fertility they must all be present. The word atmosphere, in the same way, includes a number of conditions. The investigator of nature searches out these conditions ; and by clearly pointing out in a particular case what part certain elements of the soil, atmosphere, and water, play in the growth of plants, he offers in this way an explanation of the growth i.e., the increase in mass of a plant, so far as it is explicable. When the smith makes a bar of iron red hot in his 26 LETTERS ON CHEMISTRY. forgo, it becomes covered with a black porous crust, accom- panied by the emission of sparks ; and this crust, under the stroke of the hammer, separates in scales : the iron bums. Under similar conditions, oil burns in our lamps with the emission of flame. The philosophic inquirer asks, What is the combustion of iron and of oil ? What precedes it, what follows it ? What are the conditions what the results of then* combustion ? The combustion of iron, of oil, pre- supposes the existence of iron, of oil, of air, and a high temperature. What is iron, what is oil ? There are many kinds of oil. The word oil is a collective name for certain vegetable and animal substances which contain three totally different elements. One constituent alone of the atmosphere ,i plays a part in the combustion. By combustion iron in- / creases in weight, and the air in which it has taken place I \ diminishes in weight in the same proportion. Air in which oil burns becomes heavier, and its increase in weight is equal to that of the oil consumed. The result of the combustion of iron and oil is thus perfectly clear ; the iron which has been burnt is iron which has combined with a constituent of the atmosphere. The evolution of light and heat accom- panied the union of the element of the air with the iron, and the conversion of the constituent of oil into air. The main point of the phenomenon of combustion is thus explained. By inquiring still further, whence come the light and heat during combustion ; why does the iron not continue to burn, whilst this takes place with the oil in the lamp ; why this phenomenon is accompanied in the former with the emission of sparks, in the latter with flame ; and by taking the same steps to solve these questions as in the first instance, the scientific man arrives thus at the explanation of the individual parts of the phenomenon. The philosopher of the present day explains a phenomenon by seeking out the causes which have preceded it. To those which are manifest to the senses, he gives the name of Conditions ; and that of Forces to those which are not thus manifest. According to this method of explaining phenomena, TRUE AND FALSE EXPLANATIONS. 27 inflammation of the mucous membrane of the nose is not the cause of catarrh, for this expression is only an explanation of the word catarrh. The explanation of fever involves in its meaning not a picture, or description of the state or symptoms of fever j but we wish it further to convey what has preceded the state of fever, and what makes it continue. In the explanation of the process of respiration we want to know what part the air, and what the blood plays in the production of animal heat. If the causes of phenomena are unknown, or uninvestigated, the philosophic inquirer leaves them open questions. If he finds iron in the blood, lime in the bones of animals, and does not know their source, you do not find him ready to pronounce them productions of the vital process j if he can- not tell the origin of microscopic animals, he does not set them down to be of spontaneous origin ; if he finds a body consumed by fire in a closed room, he does not assert that the individual has perished by spontaneous combustion. Conclusions and explanations of this kind he regards only in the light of self-deception, or as a cloak for ignorance. To the mind of such a man the term explanation means making clear, for which light or insight are necessary, and to him the explanation of an event is incompatible with the complete ignorance of this event. The discovery of the conditions of a phenomenon is the first and most important requisite for its explanation. They must be ascertained and established by observation. The mode of inquiry and observation depends 011 the art of the scientific man ; the skilful putting of the questions displays the powers of his mind. Let us only picture to ourselves how difficult it is to set about looking for an object which has been lost only yesterday, or eight days ago. We most certainly shall not find it by tearing up the floor, or by pull- ing down our house and searching the rubbish ; but most probably we shall succeed by reflecting in what place it was last seen or was in our possession. By first seeking without reflection we may possibly find it, but we ensure our success by first reflecting and then seeking. In the same manner 28 LETTERS ON CHEMISTRY. reflection is the only trustworthy guide in investigating the causes of a phenomenon ; by observation we discern the visible characters of the way. There is no art so difficult as that of observation ; it requires a cultivated, sober mind, and a well schooled experience, which is only acquired by long practice. The man who only sees with his eyes an object before him, has no claim to the title of an observer, which is reserved for him only ivho takes notice of the different parts of the object, and sees the connection between the parts and the whole. Many individuals overlook the half of an event through carelessness ; another adds to what he observes the creations of his own imagination ; whilst a third, who sees sufficiently distinctly the different parts of the whole, confounds together things which ought to be kept separate. In the Gorlitz trial in Darmstadt, the female attendants who washed and clothed the body observed on it neither arms nor head ; another witness saw one arm and a head of the size of a man's fist ; a third, a physician, saw both arms and a head of the usual female size. By the evidence of these witnesses we at once recognise their different degrees of information, and their capacity to make observations. The art of observing is like a piece of glass destined for a mirror, which requires to be polished with the utmost care, to produce the reflection of a clear and undistorted image. The observer of a clock does not, like a child, behold only the swinging pendulum, the dial, and hands in motion ; but he notices also the divisions of the hours, and observes the connection which exists between the suspended weights, the wheel-works, the pendulum, and the motion of the hands. As the organs of the senses and the nerves are the instru- ments of the mental acts of the observer, by which those impressions are received and transmitted, which serve as the basis of his conclusions and inferences, it follows, that individuals whose nervous sj^stems are not in a thoroughly healthy state, are not qualified to make observations. We can hence understand why mesmerism has not been NATURAL LAWS. 29 admitted into the domain of natural science ; for no intelli- gent person can believe in the proof of the existence of a new force of nature, obtained by so false a method as by the phenomena of sight and touch called forth in diseased nervous persons. If an observer has ascertained the reason of a phenomenon, and is able to unite all its conditions, he is in a position by repeating at will the phenomenon, to test the correctness of his observations by experiment. To make a series of experiments is often but another mode of expressing the decomposition of a thought into its individual parts, so as to test it by phenomena manifest to the senses. The natural philosopher makes experiments to test the correctness of his apprehension of a phenomenon, by exhibiting it in all its different phases. We apply the simple expression, natural law, to a series of phenomena, if we are able to show that they are all effects of the same cause. We speak of a simple property as a natural law, if it is applicable to the explanation of one or more natural phenomena. Thus the rising of the mercury in the Torri- cellian tube, or the elevation of a balloon, is referred to the natural law, that the atmosphere possesses weight. In conformity with our experience, a single natural phenomenon is never produced by a single cause, but by the simultaneous action of several natural laws. The state- ment of the connection of these natural laws is called the theory of the phenomenon. The theory of the barometer embraces three natural laws ; viz., that the atmosphere pos- sesses weight, that pressure on fluids is propagated uniformly in all directions, and that pressure acting in one direction witlwut any counter-pressure, produces a motion which con- tinues until equilibrium is restored. The theory of the balloon is based on the last law, on that of the pressure of the atmosphere, and on a fourth law, that a body immersed in a fluid loses a portion of its weight, exactly corresponding to tJie weight of the fluid displaced by it. Theory is thus the general term applied to the exposition of the connection of all those natural laws SO LETTERS ON CHEMISTRY. by the joint action of which a phenomenon or incident is determined. By an exact knowledge of a fact, of an event, we are in a position to explain other facts and other events. Under certain circumstances, each property of a body is, so to speak, a key to open a door which is shut to us ; theory is, however, the master key with which all doors can be opened. The word theory, to the mind of the natural philosopher, conveys thus a meaning widely differing from that which it bears in common parlance. In the latter case it is often the mere expression of what is opposed to experience or practice ; and frequently denotes defective acquaintance with facts and natural laws. In the sense of the natural philosopher theory is the sum of all practice, and is derived from the most exact knowledge of facts and natural laws. The word practice used here in opposition to theory, is not to be confounded with the term applied to the practical dexterity of an individual in an art or manufacture. A practical physicist furnishes to the mechanic the precise details for making a correct thermometer or barometer ; he tells him how to graduate the tube, and describes to him the properties of mercury, though he cannot himself make a thermometer, because he has not learned glass-blowing. The practical chemist, with the greatest exactness, informs the manufacturer of sulphuric acid, how much sulphur is to be burnt in his furnace in a given current of air for the production of the maximum quantity of sulphuric acid ; but he is not on that account qualified to manufacture with profit sulphuric acid on a large scale. He points out to the agriculturist the necessary ingredients of a soil for the production of the largest crop of potatoes, though he doos not himself know the proper period of spring for planting potatoes. He prepares quinine from bark, with- out in the slightest degree knowing the proper doses for the different states of disease. He makes physiologists acquainted with the nature and properties of the consti- tuents of blood, or of the secretions in healthy and diseased states of the body, without necessarily possessing any THEORY AND PRACTICE. 31 knowledge of the phenomena of disease and their relations to the vital process. This kind of practice, which is based on the technical application of natural laws, famishes a rule to estimate the dexterity of the glass-blower, and of the manufacturer of sulphuric acid, or to ascertain the experience of the agriculturist and physician, or the knowledge of the physiologist ; but it affords no measure of the practical capacity of the chemist. He has to learn practically the laws of nature, the method of investigating them, and the principles of their applications. Hence the study of other branches of the natural sciences, and a knowledge of mathematics and of chemical manufac- tures, is an indispensable necessity to him. His most important problem is the investigation of the properties of bodies and their manifold compounds ; for all practical applications of chemistry rest on a knowledge of these properties. Thus the new art of photography is founded on a knowledge of the properties of four chemical compounds : viz., on the change produced by the influence of light on chloride and iodide of silver ; on the reconversion of the altered silver compound into metallic silver by means of pyrogallic acid or some other reducing agent ; on the solu- bility of silver compounds in water containing sea-salt or hyposulphite of soda ; and finally on the solubility of col- lodion in alcohol. Chloroform finds application in surgical practice from its volatility and incombustibility in the blood. We have indicated in the preceding pages the means employed at the present day to become acquainted with the natural sciences, the problems which chemistiy proposes to herself, and the qualifications necessary in chemists to solve those problems. The utility of the study of chemistry requires no further arguments in its favour. Our object is not now to discuss the question of utility, but science ; for science is always useful, in as much as every species of knowledge augments the mental and corporeal powers. We study a natural pheno- menon without inquiring into its utility ; for there are many which are not applicable to the purposes of life. The rain- 32 LETTERS ON CHEMISTRY. bow which, in its celestial beauty, awakens in eveiy human breast feelings of hope and confidence, offers no direct benefit to man, and yet it forms as fine an object of natural study as any practical questions, such as the conversion of sea- water into fresh, or the protection of butter from rancidity. If in the manifold development of chemistry there still exist gaps, we must bear in mind, that it is like eveiy natural science in a progressive state. By degrees these gaps will be filled up, but their entire disappearance from so vast a domain can never be hoped for. We have this advantage over the Greek philosophers, that, as far as regards those very subjects, on which we might be supposed to possess information, we are infinitely better aware than Socrates himself, that we know nothing. We ascend a mountain, and gain its summit, only to behold by the more extensive prospect other mountains rising above us, and which were before concealed from our eyes. If we endeavour from this elevated spot to take the widest range of view, it will then prove easier to find our way in the regions which lie beneath us, to guard ourselves from straying, and from obstructions which lie in our path and exhaust our strength. The domain which we see from this commanding point lying beneath us becomes, as it were, our acquired property, in which we can apply our efforts with advantage to ourselves and others. The history of man is the mirror of the development of his intellect. It shows us in his acts, his faults and frailties, his noble qualities, and his imperfections. The investigation of nature teaches us to recognise the omnipotence, the perfection, and the inscrutable wisdom of an infinitely higher Being, in his works and actions. So long as we are ignorant of these things, the perfect development of the human mind cannot be hoped for, or even conceived. With- out this knowledge the immortal spirit of man cannot attain to a consciousness of its own dignity, or of the rank which it occupies in creation. The religion of the Greeks and Romans of the heathen was, in its origin, founded upon an imperfect contemplation IMMENSITY OF THE UNIVERSE. 33 and false impression of natural phenomena. Those nations were intellectually blind to the immediate causes of the changes and fluctuations in things around them. They directed their prayers to the gross the more obvious powers of nature. Every superstition carries us back to heathenism. The exalted value, the sublimity of a right comprehension of nature, lies precisely in this, that it is the medium for a correct apprehension of Christian truth. And the divine origin of true Christian doctrine, indeed, is proved by the fact that we are indebted for it, and for a correct notion of a Being who is above all worlds, not to the imperfect way of empirical investigation, but to a higher enlightenment. The space in which the sj^stems composing the universe move, is illimitable. Were we to attempt to assign its limits, what could we imagine to be beyond? The number of worlds is infinitely great ; it is inexpressible, indeed, by numbers. A ray of light traverses 180,000 miles in a second of time. A year comprises millions of seconds, yet there are fixed stars so immeasurably distant that their light has required billions of years to reach our eyes. We are acquainted with animals possessing teeth, and organs of motion and digestion, which are wholly invisible to the naked eye. Other animals exist, which, when measured, are found to be many hundreds of times smaller, and which, nevertheless, possess the same apparatus. These creatures, in the same manner as the larger animals, take nourishment, and are propagated by means of ova which must consequently be, again, many hundreds of times smaller than their own bodies. It is only because our organs of vision are imperfect that we do not perceive creatures a thousand times smaller than these. What variety and what infinite gradations do the con- stituents of our globe present to us in their properties and their conditions ! There are bodies which are twenty times heavier than an equal volume of water, there are others which are ten thousand times lighter, the ultimate particles of which cannot be seen by the most powerful microscopes. Finally, we have in light, that wonderful 34 LETTERS ON CHEMISTRY. messenger which brings us daily intelligence of the continued existence of numberless worlds, the expression of an extra-terrestial essence which no longer obeys the laws of gravitation, and yet manifests itself to our senses by innumerable effects. Even the light of the sun with the arrival of which, upon the earth, inanimate nature receives life and motion we cleave asunder into rays, which, without any power of illumination, produce the most important alterations and decompositions in organic nature. We separate from light certain calorific rays, which exhibit among themselves a diversity as great as exists amongst colours. But nowhere do we observe either a beginning or an end. The human mind perceives in nature no limit either above or below itself, and in this infinity, scarcely conceivable, since it is in both directions unfathomable by human power, not one drop of water falls to the ground, not one particle of dust changes its place, without compulsion. Nowhere beyond the sphere of his own being does man per- ceive a conscious will ; he sees everything around him bound in the chains of invariable, immutable, fixed laws. Within himself alone he recognises a something which may govern these effects, a will which has the power to rule over all natural laws, a spirit which, in its manifestations, is independent of these natural powers, and which, when it is in its conceivable perfection, is subject only to its own laws. The mere empirical knowledge of nature forces upon us, irresistibly, the conviction that this something within us is not the limit beyond which there exists nothing similar or more perfect. The inferior gradations only of this something are accessible to our powers of perception. And this convic- tion, like every other truth in inductive natural investiga- tion, affirms the existence of a higher, indeed of an infinitely exalted Being, to contemplate and to comprehend whom our senses are too feeble, and of whom, in his greatness and sublimity, we can only form some conception by the highest cultivation of every faculty of our minds. The knowledge of nature furnishes us with the most STUDY OF SCIENCE IMPORTANT. 35 effectual means of advancing onr intellectual powers to this degree of perfection. The history of philosophy informs us that the wisest men, the most profound thinkers of antiquity, and, indeed, of all ages, considered the insight into the essence of natural phenomena, the acquaintance with natural laws, as an indis- pensable means for cultivating the mind. The study of external nature physical science constituted a part of phi- losophy. Science renders the powers of nature the servants of man, whilst empiricism subjects man to their service. The empiric, placing himself on a level with an inferior or unconscious being, employs but a small portion of his powder for the advantage of society. He permits effects to govern his will, whilst, by a true insight into their hidden connec- tions, he might govern them. The pertinence of these remarks will be apparent when I attempt, in a subsequent chapter, to explain one of the most remarkable laws which lies at the foundation of modem Chemistry. If to the comparative anatomist, a small fragment of bone, a tooth, serves as a volume from which he can relate to us the history of a being belonging to a past world, de- scribe its size and shape, point out to us the medium in which it breathed and lived, and demonstrate to us of what its nourishment consisted, whether animal or vegetable, and its organs of motion, all this might be supposed to be the mere creation of a lawless imagination, if this small frag- ment of bone, this tooth, owed its form and constitution, to mere chance. But the anatomist may safely assert all this as a reality, because every particle owes its form to definite laws, and because, when the form of a part is once known, it indicates the mode of construction of the whole. It may not appear less wonderful to many that the che- mist should be able, when he knows the proportion in which any single substance unites with another substance, to dis- cover and to fix the exact proportion in which the former will unite with all other bodies whatever. The discovery of these laws, to which all the processes D 2 36 LETTERS ON CHEMISTRY. comprising number and measure are subordinate, in organic as well as in inorganic nature, and which regulate and govern all chemical actions, is acknowledged to be the most im- portant acquisition of the present centuiy, and the most pro- ductive in its results. ORIGIN OF CHEMISTRY. 37 LETTER III. Origin and progress of Chemistry The Philosopher's Stone and the Trans- mutation of Metals Alchemy and the Alchemists Learning of the Alchemists True nature of Alchemy, it was the Chemistry of the period The wonders of modern science exceed the wildest dreams of Alchemists The theory of Phlogiston useful at the time in classifying facts and in generalisation Stahl Cavendish Black Lavoisier The Anti-phlogistic Theory The three periods of Science. IT is not easy to form an idea of the extent of chemical knowledge at the present day without casting a glance back to past ages. The history of science fills a page in the his- tory of the human mind ; and there is no department of science, the history of which is more interesting and instruc- tive, in reference both to its origin and to its development, than chemistry. The received belief of the recent origin of that science is an error, originating in accidental cir- cumstances. Chemistry is one of the very oldest of the sciences. The same spirit which, towards the close of the last cen- tury, aroused in a highly civilised nation the insane endeavour to annihilate the monuments of its history and of its glory, which raised altars -to the Goddess of Keason, and intro- duced a new calendar ; that spirit gave rise also to a festival in which Madame Lavoisier, robed as a priestess, committed to the flames on an altar, while a solemn requiem was chanted, the phlogistic system of chemistry. At that period, the chemists of France associated themselves for the purpose of changing all the names and symbols which had been employed up to that time to designate chemical compounds, and to represent chemical processes. A new nomenclature was introduced, which, in the train of a new and complete system, soon secured for itself a universal reception. This, then, was the origin of the apparently wide gulf separating 38 LETTERS ON CHEMISTRY. modern from ancient chemistry. The history of every important discovery, of every separate observation, made up to the time of Lavoisier, in any part of Europe, was then blotted out ; while new names and altered views tore asunder all connection with the past. To man}', the knowledge we now possess appears to be only the inheritance of the French school of that day ; and 4he histoiy of true chemistry is supposed to reach 110 further back. But it is precisely here that the fallacy lies. As in the history of nations there is no event which has not been preceded by other events or circumstances of which it is the consequence, so is it with the progress of all the natural sciences. In the same way as a phenomenon in any department of nature, living or dead, presupposes the con- ditions under which it has arisen, so is the progress of natural science prepared by the previous acquisition of truths, which are either facts, or conclusions dependent upon and deduced from facts. A new system or a new theory always follows from observations, more or less comprehensive, which contradict the reigning doctrine. In the time of Lavoi- sier, all the substances and all the phenomena which ho studied, were already known. He discovered no new body no new property no natural phenomenon previously un- known ; but all the facts established by him were the neces- sary consequences of the labours of those who had preceded him. His merit, his immortal glory consisted in this that he infused into the body of the science a new spirit ; but all the members of that body were already in existence, and rightly joined together. Chemistry embraces the effects produced by natural forces, of the most recondite kind which do not, like many physical forces or influences, such as light or gravity, make themselves known in forms of action daily arresting our attention. These forces do not act at sensible distances, but are only manifested in their results when different kinds of matter- are brought into the closest contact. Ages were required to collect the world of phenomena of which chemistry consisted before Lavoisier appeared. It required innumerable obser- PEOGRESS OF CHEMISTRY SLOW. 89 vations before men were able to attempt the explanation of that most striking though familiar phenomenon, the burning of a candle before they could seize the hidden clue, which led to the conclusion, that the rusting of iron in the air, the bleaching of vegetable colours, and the respiration of animals, were all dependent on the same cause as the combustion of inflammable substances. In order to attain that knowledge of chemistry which we now possess, it was necessary that thousands of men, armed with all the science of their respective periods, and inspired with an unconquerable ardour, with a passion for knowledge, which, in its violence, bordered 011 madness, should devote life, fortune, and their whole faculties, to the task of exploring the earth in all directions. It was necessary that, with indefatigable perseverance and constancy, these men should bring into contact all known substances, organic and inorganic; it was necessary that these labours should be continued for fifteen centuries. There was, finally, a mighty, an irresistible charm, which urged men to devote themselves with an amount of patience and perseverance altogether unexampled in history, to labours which did not tend to supply any want peculiar to the time in which they lived. This mighty impulse was nothing else than the desire for earthly happiness. By a wonderful and wise dispensation, there was implanted in the minds of the wisest and most experienced men the idea of the existence of a thing, hid in the bowels of the earth, by the discovery of which man might become pos- sessed of those things which imply the gratifi cation of the utmost desires of a refined sensuality namely, gold, health, and long life. " Gold gives power ; without health there is no enjoyment, and longevity here takes the place of immortality." (Gothe.) These~^hree primary essentials of earthly happiness were supposed to be united in the "philosopher's stone." For more than a thousand years, the grand, the ultimate object of all chemical labours was the search for that " virgin earth" coveted as the means of preparing the mysterious 40 LETTERS OX CHEMISTRY. substance which, in the hands of the philosopher or wise man, changes every base metal to gold, and which, according to a later creed, when used as a remedy in its highest perfec- tion, cures all diseases, restores youth to the exhausted frame of age, and prolongs life indefinitely. Rightly to appreciate and judge of the true nature of alchemy, we must remember, that till the sixteenth century the earth was regarded as the centre of the universe, and that the life and destiny of men were believed to stand in the closest relation to the motions of the heavenly bodies. The universe was a vast whole, an organism, the members of which stood in an uninterrupted relation of reciprocal influ- ence. " From all the ends of heaven the creative forces radiate towards the earth, and determine earthly destinies." (Roger Bacon.) "When a man," says Paracelsus, "eats a bit of bread, does he not therein consume heaven and earth and all the heavenly bodies, inasmuch as heaven, by its fer- tilising rain, the earth by its soil, and the sun by his luminous and heat-giving rays, have all contributed to its production, and all are present in the one substance ? " All that hap- pened on earth stood written in starry characters in heaven. All that was thus written in heaven must of necessity happen on earth. Mars, Venus, or some other planet, ruled, from birth, the actions and the fortunes of individual men, while comets, lawless in their appearance, were the threatening symbols of want and woe to entire nations. The knowledge and study of nature and of her powers included the science of magic, which, when combined with the healing art, was regarded as the true idea of secret wisdom. In the phenomena of organic life in the vast operations of nature in thunder and lightning, storm and hail, men recognised the agency of unseen spirits. What- ever insight a thinking man might have acquired by observa- tion, was to him a possession; the source of which was not perceived by the multitude ; it was a sign or mark of his intercourse with supernatural beings, and his knowledge became, in the eyes of the ignorant, the power by which he controlled the world of spirits. " Demons," says Ceesalpinus, ALCHEMY. 41 " perceive by the inward mind, without requiring the aid of bodily senses, but without natural means they can exert no influence on men or animals. Those which are of an evil sort produce bewitchments and all kinds of mischance." " During four centuries, European jurisprudence sacrificed thousands of human victims to the belief in the existence of compacts between men and the evil one. The world was firmly convinced of the existence of such compacts, although these were of the most strange description, inasmuch as none of the parties to them derived any benefit from the agreement. For the unfortunates who had signed away their souls to the devil lived, for the most part, in the deepest poverty and misery, not even gaining earthly plea- sures by the exchange, while their share of heavenly bliss gained by the enemy of mankind, was, to him, a worthless possession." (Carriere.) When compared with this stage of development of the human intellect, alchemy, as far as regards a knowledge of natural truths, was in advance of other natural sciences. Chemistry, at that time, and up to the fifteenth century, stood on the same level, it was no further back in its development than astronomy. The idea of the philosopher's stone, considered as a means of transmuting the baser metals to gold, was spread abroad from Egypt, chiefly by the Arabians. By the conquest of Egypt, they acquired possession of natural and scientific truths, perhaps originally attained by a jealous caste of priests, and which, being taught as mysteries in the temples, were accessible only to the initiated. Even Herodotus and Plato had early obtained instruction and knowledge in that remarkable country. Nine hundred years before the con- quest of Egypt by the Arabs, the Alexandrine Academy already supplied a centre of scientific activity, and even down to the period of the burning of the vast library by the Arabs, Alexandria was the seat and the refuge of Grecian science. Among the Arabs, a people intellectually new and fresh, whose Mahometan fatalism opposed to the develop- ment of medicine, and whose maxims, derived from the 42 LETTERS ON CHEMISTRY. Koran, expressly prohibiting research and reflection, were yet unable to check the progress or prevent the encourage- ment of the sciences, of medicine, astronomy, and mathema- tics; among these Arabs the views of the Alexandrian philosophers concerning the transmutation of metals found a prepared and fruitful soil ready for their reception. At the time when Bagdad, Bassora, and Damascus were the centres of the commerce of the world, there was no nation more dexterous or more active in trade, or more eager for gain and gold, than the Arabs. Their tales and legends have preserved for us the favourite dreams and desires of that period, which were the motives of Arabian enterprise and activity. While the elves and nixes, the dwarfs and Undines, of the Germanic legends, appear as the bestowers of swords which no foe could withstand, or of unguents which healed every wound ; of wine-cups ever full, or of tables ever-loaded with food ; the genii of the Thousand and One Nights are always the guardians of immeasurable treasures, of gardens, whose trees are of gold and their fruits of precious gems. The wonderful lamp of the Arabian romancers, by means of which man could come into pos- session of these treasures, was obviously regarded as some- thing as tangible and attainable as was the broomstick on which, many centuries later, the witches of -Germany rode through the air to the Blocksberg, there to celebrate in wild and maddened dance the festival of the Walpurgis night (1st of May). In Egypt, this mysterious object of desire took the form of the philosopher's stone. From the Arabian universities, the endeavour after the discovery of the philosopher's stone, and with it, the acquisi- tion of chemical knowledge, and the whole direction given to scientific research, was communicated to the north-west of Europe. On the model of the schools of Cordova, Seville, and Toledo, which had been' frequented, since the tenth century, by the studious of all countries in their earnest pursuit of knowledge, there arose in Paris, Salamanca, Padu,a, and many other cities, universities, seats of the sciences ; and in accordance with the cultivation of the period, the LEARNING OF THE ALCHEMISTS. 43 Christian clergy became the only possessors of the knowledge obtained by the researches of the Arabian philosophers, and the only persons capable of extending to the world the learning thus acquired. Many centuries later, the prover- bially dark and mysterious explanations of the Egyptian priests, their mystical, figurative style, mixed up with religious ideas, continued to be peculiar to alchemy, the chemistry of the age. The writings of Geber, the Pliny of the eighth century, give evidence of an extent of chemical knowledge, of facts experimentally established, which, when the period is con- sidered, excites our wonder and admiration ; and the theories of the great philosophers of the thirteenth century, Roger Bacon and Albert von Bollstadt (Albertus Magnus), Bishop of Ratisbon, may, for their fertility of ideas, and their comprehensive views of nature, be fitly compared only with those of the modem schools of natural science. We classify bodies, at the present day, in groups, accord- ing to similarity or identity of properties; but the same thing was done in Geber' s time. The metals possess in common certain fundamental properties ; all of them have the metallic lustre. Some metals are unchangeable in the fire ; these were the so-called noble or perfect metals. But the greater number, when exposed to the action of fire, lose their lustre and malleability ; these were the base metals. Besides these, there was a third class, called the imperfect or semi-metals. At that period, lead-glance (or galena) and iron pyrites, having the metallic lustre, could not be separated or distin- guished from metals. The former had the colour of lead, the latter approached in colour to gold. From both minerals, sulphur could be expelled ; the lead-glance yielding, when thus treated, and without change in its lustre or colour, true, metallic, malleable and fusible lead. What was more natural than to conclude, that sulphur was an ingredient of the baser metals, the amount of sulphur determining their properties 1 Since then, lead-glance, by the expulsion of a certain quantity of sulphur, was converted into lead, was it not probable, that 44 LETTERS ON CHEMISTRY. by the removal from lead of somewhat more sulphur, we might attain to a still higher purification or refinement of the metal, and thus convert it into silver 1 In fact, by further treatment with fire (by the process of cupellation), a certain quantity of silver was obtained from the lead, and from the silver a trace of gold was separated. These three metals thus merely separated from each other by the alchemist, were regarded by him as the actual pro- ductions or creations of his processes. Was it not then probable that by perfecting his processes he would ultimately be able to convert all his galena into silver, and all his silver into gold 1 Experience had already demonstrated that each improvement in his mode of experimenting was attended with an increase in the proportion of lead, silver, and gold obtained from the same quantity of galena. The volatility of mercury was known. What was more natural than to conjecture that the loss of metallic pro- perties, in the calcination of the imperfect metals by fire, or that the rusting of such metals in the air, depended on the escape of the volatile mercury ? Even at the present day, common experience leads us to suppose, in all coloured bodies, the presence of a colouring matter, The red of the ruby, the green of the emerald, and the blue of the sapphire, depend on causes analogous to those which determine the colour of dyed textures. Soft or malleable iron may be rendered hard by the addition of a small proportion of a foreign body; by a certain process, hard cast-iron may be rendered soft and malleable ; copper, which is red, acquires a colour like that of gold, when heated with calamine (zinc ore), and may be rendered silver white by means of arsenic ; gold itself, when heated with sal ammoniac, acquires a reddish tinge, while borax gives it a pale colour. Even our children are in the habit of k changing iron into copper,' as they imagine, when they I immerse a knife in ink (containing sulphate of copper), Un which experiment the iron, becoming coated w.ith copper, seems to disappear. Finally, the sand of certain rivers, when heated with certain fluxes, was known to yield TRANSMUTATION OF METALS. 45 gold ; and red earth, ignited with oil, was found to be a source of iron. What, then, was more natural to the inexperienced mind than to believe, that the properties common to all metals depended on substances, on certain ingredients ; that by the removal or addition of certain matter^, lead or copper might acquire the properties of silver or gold ; that an imperfect tincture might give the colour, while a more perfect one would supply the other desired qualities ? No one can wonder that the old alchemists should have regarded as metals the compounds of metals with sulphur (sulphides, such as lead-glance or pyrites) ; especially when he remembers that the chemists of our day for twenty-six years considered and described as metals an oxide of a metal (protoxide of uranium), and a compound of a metal with nitrogen (nitride of titanium). " There are," says Geber, " as is proved by the facts above narrated," which in his point of view were certain and con- clusive, "means of producing and transmuting metals. These means consist in three sorts of medicines. Those of the first order are the raw materials, or ores, as furnished by nature. Those of the second order are the substances of the first order, after being refined and purified by chemical processes. By the further ennobling and fixing of these is produced the medicine of the third order. This is the great Magisterium, the red tincture, the great elixir, the philoso- pher's stone." In all metals, according to the creed of the alchemists, there is contained a principle, which gives to them the metallic character. This is the mercury of the adepts. To increase the proportion of this principle in the baser metals is to ennoble them. If we extract this metallic principle from any body or metal, if we increase its power by refining it, and thus produce the quintessence of all metallidty (to coin a word), we have the stone which, when made to act on base or unripe metals, matures and ennobles them. The mode of action of the philosopher's stone was considered by many as analogous to that of a ferment. " Does not yeast 46 LETTERS ON CHEMISTRY. change the juice of plants or a solution of sugar, by a new arrangement of their particles, into the youth-giving and invigorating water of life ? (aqua vitce, alcohol). Does it not effect the expulsion of all impurities ? Does not a ferment (sour dough) convert flour into nourishing bread ? " GEORGE RIPPEL, 15th century. In its utmost perfection, as the universale, one part, accord- ing to Roger Bacon, sufficed to transmute a million parts according to Raymond Lully, a thousand billions of parts of a base metal into gold. According to Basil Valentine, the power of the philosopher's stone extends only to seventy parts ; and John Price, the last alchemist and gold-maker of the eighteenth century, describes it as transmuting only from thirty to sixty parts of base metal. For the preparation of the philosopher's stone the first requisite was the raw material, the Adamic earth, virgin <3arth, which is indeed to be found everywhere, but its dis- covery is dependent on certain conditions known to the initiated alone. " When we have once obtained this," says Isaacus Hollandus, "the preparation of the stone is only a labour fit for women, or child's play. From the materies prima, cruda or remota, the philosopher obtains first the mercury of the adepts, which differs from ordinary quick- silver, and is the quintessence, the first condition, of the creation or procreation of all metals. To this is added philosophical gold, and the mixture is left for a long time in an incubatory or brooding furnace, which must have the form of an egg. There is thus obtained a black substance, the raven's head, or caput corvi, which, after long exposure to heat, is converted into a white body. This is the white swan, cygnm albus. After this has been long and more fiercely heated, it becomes yellow, and finally bright red, and now the great work is consummated." Other accounts of the process for preparing the philo- sopher's stone are rendered, by their being mixed up with mystical views, yet darker and more mysterious. The custom, too, prevalent in those ages, of regulating divisions of time by the hours of prayer passed, during the tenth, THE PHILOSOPHER'S STONE. 47 eleventh, and twelfth centuries, into the laboratories of the alchemists ; and it is easy to perceive how, by degrees, the success of the operation came to be regarded as essentially dependent on the efficacy of prayers, which prayers were at first used only to determine its duration. In the seventeenth century, the transformation of alchemistical ideas into reli- gious notions had become so complete, that alchemistical expressions were frequently employed to designate religious ideas. In the writings of the mystics, (for example, in those of the visionary Jacob Bdhme, t!624,) the term " philosopher's stone " no longer signifies the substance which transmutes baser metals into gold, but " conversion ; " the clay furnace is " the earthly body ; " and the green lion is " the Lion of David." Previous to the invention of printing, it was easy for an alchemist to keep secret his discoveries. He exchanged them only for the observations of other adepts. The chemical processes which they published are clearly and intelligibly described, in so far, at least, as they are not such as to lead to any practical result in reference to the chief object of their search ; but they expressed their views, and described their labours, 011 the subject of the grand arcanum or Magis- terium, in figurative language and in mysterious symbols. They propounded in an unintelligible language that which, in their own minds, was only the faint dawn of an idea. That which chiefly excites our wonder is, that the existence of the philosopher's stone should have been regarded, for so many centuries, as a truth established beyond all doubt, while yet no one possessed it, and each adept only maintained that it was in the possession of another. Who, indeed, could entertain a doubt, after Van Helmont had declared, in 1618, that on several occasions there had been sent to him, from an unknoivn hand, one-fourth of a grain of the precious material, with which he had converted into pure gold eight ounces of quicksilver 1 Did not Helvetius, the distinguished body physician to the Prince of Orange, and the bitter opponent of alchemy himself relate, in his " Vitulus aureus quern mundus adorat et orat" (1667,) 48 LETTERS OX CHEMISTRY. that he had obtained the most convincing proofs of the existence of the philosopher's stone 1 For he, the sceptic, had received, from a stranger, a fragment of the size of half a rape seed, and therewith, in presence of his wife and son, had transmuted six drachms of lead into gold, which stood the tests applied to it by the Warden of the Mint at the Hague ! Were not two pounds and a half of quicksilver converted into pure gold, of which a large medal was struck (Kopp. Geschichte der Chemie, II. 171), representing the figure of the God of Day (Sol or gold) holding the caduceus of Mercury, to indicate the origin of the precious metal from mercury, with the legend DIVINA METAMORPHOSIS EXHIBITA PRAGUE, xv. JAN., AN. MDCXLVIII, IN PRESENTIA SAC. C^ES. MAJ. FERDINAND: TERTII, etc. ? Was not this done at Prague, in presence of the Emperor Ferdinand III. (1637-1657) by the head surveyor of mines, Count von Russ, with the aid of one grain of a red powder, which he had received from a certain Richthausen, and he again from an unknown ? (According to J. F. Gmelin, this medal was still extant in 1797, in the treasuiy at Vienna.) The Landgrave of Hesse Darmstadt also, Ernst Ludwig, as we are told by the alchemists, received, from an unknown hand, a packet containing red and white tincture, with directions for their use. Ducats were coined of the gold which he had made from lead by this means, and from the silver thus obtained were coined the Hessian specie dollars (Species thaler) of 1717, on which is the legend Sic DEO PLACUIT IN TRIBU- LATIONIBUS. (Kopp. II. 271.) It can hardly be doubted that the amateurs of alchemy in these cases experienced something similar to that which befel the distinguished and highly deserving Professor of Theology, Joh. Sal. Semler in Halle (t!791), who occupied himself at one time in experiments with a then renowned universal medicine, which was offered for sale under the name of atmospheric salt (Luftealz) by a certain Baron von Hirsch. Semler thought he had discovered that gold grew, or was produced in this salt when kept warm and moist. He sent, in 1787, a portion of the salt with the gold grown in it to SUPPOSED GROWTH OF GOLD. 49 the Academy of Sciences, at Berlin. Klaproth, who examined it, found it to contain glauber salt (sulphate of soda) and sulphate of magnesia, enveloped in a magma or extract of urine, and gold leaf in considerable quantity. Semler also sent to Klaproth some of the salt in which no gold had yet grown, and a liquor which " contained the germ of gold, and which impregnated the atmospheric salt in a proper warm temperature." It appeared, however, that the salt was already mixed with gold. Semler firmly believed in the production of the gold. In 1788 he wrote, "Two glasses are bearing gold. Every five or six days I remove it ; each time about twelve to fifteen grains. Two or three other glasses are in progress, and the gold blooms out below." A new portion which was sent to Klaproth in leaves of from four to nine inches square proved that the gold plant had unfortunately degenerated ; for now it bore adulterated gold or pinchbeck. At last the matter was cleared up. Semler' s servant, who had to take care of the hothouse, had intro- duced gold into the glasses, in order to give his master pleasure ; but being on one occasion prevented from doing so himself, his wife undertook the business ; but she was of opinion that pinchbeck leaf was much cheaper and would serve the purpose equally well. In the fourteenth, fifteenth, and sixteenth centuries, how- ever, men were not so familiar with the means of distin- guishing genuine gold and silver from alloys of similar appearance as in the time of Semler. The impostures, which were practised on a great scale by the makers of gold, were not sufficient to weaken the popular belief in the reality of the transmutation of metals. Henry VI., of England, in 1423, in four successive decrees, summoned all nobles, doctors, professors, and clergymen to devote themselves, according to their several abilities, to the study of the art, in order to procure the means of discharging the debts of the state. "The clergy," said the king, "should engage in the search for the philosopher's stone ; for, since they could change bread and wine into the body and blood of Christ, they must also, by the help of God, succeed in transmuting 50 LETTEES OX CHEMISTRY. the baser metals into gold." What success attended these decrees may be gathered from the fact, that the Scottish parliament subsequently ordered a strict watch to be kept in all the harbours of Scotland, and on the^Iand frontier, in order to prevent the introduction of false money. It is said that the descendants of the gold-makers of that period still exercise their craft in Birmingham. During the sixteenth century alchemists were found iu the courts of all princes. The Emperor Rudolph II. and the Elector Palatine Frederick were known as patrons of alchemy. Men of all ranks studied transmutation, and strove to attain possession of the grand arcanum. Just as in the present day vast sums are expended by princes, private persons, and associations in mining enterprises for the discovery of metallic ores, of coal, or of strata of salt, so were vast sums squan- dered in the sixteenth and seventeenth centuries for the researches deemed necessary in order to discover the philo- sopher's stone. A multitude of adventurers appeared, who- endeavoured, at the courts of the great and mighty, to pass- for adepts, that is, possessors of the secret but this was a dangerous game : for those who at one court, or at another, succeeded, by dexterously managed transmutations, in esta- blishing their character as adepts, and carried off honours and riches as their reward, were sure finally to fail elsewhere ; and their end commonly was, to be hung in a robe covered with tinsel on a gallows adorned in a like manner. Those, again, whose imposture could not be proved, expiated the fatal honour of being believed to possess the philosopher's stone, under the hands of covetous princes, by imprisonment and tortures. Indeed, the cruel treatment which such adven- turers experienced was regarded as the strongest proof of the truth of their art. KOPP. The great (Francis) Bacon, Luther, Benedict Spinosa, and Leibnitz believed in the philosopher's stone, and in the pos- sibility of the transmutation of metals ; and the decisions of Faculties of Jurisprudence prove how deep and how widely extended these ideas had at that period become. The Faculty of Law in Leipsic declared, in 1580, in their judgment GOLD MAKING. 51 against David Bcuther, that he was proved to possess the knowledge of the philosopher's stone ; and the same Faculty, in 1725, gave a decision in the affair of the Countess Anna Sophia von Erbach against her husband, Count Frederick Charles von Erbach. The lady had granted protection, in her castle of Frankenstein, to a fugitive who was pursued and hunted like a wild beast ; and he, who was an adept, had, to show his gratitude, converted the silver plate of the countess into gold. The count claimed the half of it, because the increase in its value had been obtained on his territory, and under coverture. But the Faculty decided against him ; because the object claimed had been, before its conversion into gold, the property of the countess, and she could not lose her right of property in it by the transmutation. In our day, men are only too much disposed to regard the views of the disciples and followers of the Arabian school, and of the late alchemists, on the subject of transmutation of metals, as a mere hallucination of the human mind, and, strangely enough, to lament it. But the idea of the variable and changeable corresponds to universal experience, and always precedes that of the unchangeable. Before the intro- duction of the balance and the development of chemical analysis, there were no scientific grounds for the opinion, that iron existed, as such, in a red stone, or copper in a blue or green stone, and were not produced by the processes fol- lowed for their extraction. If the metals were products, i. e. formed by the processes, and were not educts, i. e. already existing, and only separated by the process, then were the metals capable of transmutation. Everything depended on the process employed. The notion of bodies, chemically simple, was first firmly established in the science by the intro- duction of the Daltonian doctrine, which admits the exist- ence of solid particles, not further divisible, or atoms. But the ideas connected with this view are so little in accordance with our experience of nature, that no chemist of the present day holds the metals, absolutely, for forty-eight simple, unde- composable bodies, for true elements. Only a few years since, Berzelius was firmly convinced of the compound nature E 2 52 LETTERS ON" CHEMISTRY. of nitrogen, chlorine, bromine, and iodine ; and we allow our so-called simple substances to pass for such, not because we know that they are in reality undecomposable, but because they are as yet undecomposed ; that is, because we cannot yet demonstrate their decomposability, so as to satisfy the requirements of science. But we all hold it possible that this may be done to-morrow. In the year 1807, the alkalies, alkaline earths, and earths proper, were regarded as simple bodies, till Davy demonstrated that they were compounds of metals with oxygen. In the last twenty-five years of the preceding century, many of the most distinguished philosophers believed in the transmutation of water into earth. Indeed, this belief was so widely prevalent, that Lavoisier, the greatest chemist of his day, thought it advisable, in a series of beautiful experi- ments, to submit to investigation the grounds on which it rested, and to point out their fallacy. Such notions as that of the production of lime during the incubation of eggs, and of iron and metallic oxides in the animal and vegetable vital processes, have found, even in the present century, acute and enthusiastic defenders. It is the prevailing ignorance of chemistry, and especially of its history, which is the source of the very ludicrous and excessive estimation of ourselves, with which many look back on the age of alchemy ; as if it were possible, or even con- ceivable, that for more than a thousand years the most learned and acute men, such as Francis Bacon, Spinosa, and Leibnitz, could have regarded as true and well-founded an opinion void of all foundation. On the contrary, must we not suppose, as a matter beyond a doubt, that the idea of the transmutability of metals stood in the most perfect har- mony with all the observations and all the knowledge of that age, and in contradiction to none of these ? In the first stage of the development of science, the alche- mists could not possibly have any other notions of the nature of metals than those which they actually held. No others were admissible or even possible ; and their views were con- sequently, by natural law, inevitable. We hear it said that VALUE OF A THEORY. 53 the idea of the philoospher's stone was an error ; but all our views have been developed from errors, and that which to-day we regard as truth in chemistry, may, perhaps, before to-morrow, be recognised as a fallacy. Every theory which urges men to labour and research, which excites acuteness and sustains perseverance, is a gain to science ; for it is labour and research which lead to dis- coveries. The three laws of Kepler, which are regarded as the foundation of modern astronomy, were not derived from just views of the nature of that force which retains the planets in their revolutions and in their orbits, but are simply deductions obtained by the art of experimenting ; that is to say, by labour and research. The most lively imagination, the most acute intellect, is not capable of devising a thought which could have acted more powerfully and constantly on the minds and faculties of men, than that very idea of the philosopher's stone. Without this idea, chemistry would not now stand in its present perfection ; and in order to call that science into existence, and in the course of 1500 or 2000 years to bring it to the point which it has now reached, it would have been necessary to create the science anew. It was that same force which urged thousands of adventurers, with and after Columbus, to venture fortune and life on the discovery of a new world, and which, in our day, drives hundreds of thou- sands to cross the mountains of Western America, and thus to spread cultivation and civilisation over that hitherto neglected part of the globe. In order to know that the philosopher's stone did not really exist, it was indispensable that every substance acces- sible to study and observation should be observed and examined, in accordance with the scientific resources of the time. But it is precisely in this that we perceive the almost miraculous influence of the idea. The strength of the opinion could not be broken, till science had reached a certain stage of development. During centuries, as we have seen, whenever doubts arose, and the labourers became languid in their efforts, a mysterious unknown was sure to 54 LETTERS ON CHEMISTRY. appear at the right moment, who convinced some prominent and trustworthy man of the reality of the great Magisterium. A person ignorant of science, who takes the trouble to read a single page of a Manual of Chemistry, must feel the utmost astonishment at the mass of individual facts there recorded. Almost every word, in such a book, expresses an observation or a phenomenon. These observations did not present themselves to the observer ; they were laboriously sought for and obtained. What would be the present position of science without sulphuric acid, which was dis- covered by the alchemist more than a thousand years ago, without muriatic acid, nitric acid, ammonia, the fixed alkalies, the numberless compounds of metals, alcohol, ether, phosphorus, or prussian blue 1 It is impossible to form a just conception of the difficulties which the alche- mists had to overcome in their researches ; for they were of necessity the inventors of the apparatus or instruments, and of the processes which served for the production of their preparations, and they were compelled to make with their own hands everything which they employed in their experiments. Alchemy was never at any time anything different from chemistry . It is utterly unjust to confound it, as is generally done, with the gold-making of the sixteeenth and seventeenth centimes. Among the alchemists there was always to be found a nucleus of genuine philosophers, who often deceived them- selves in their theoretical views ; whereas the gold-makers properly so-called, knowingly deceived both themselves and others. Alchemy was a science, and included all those processes in which chemistry was technically applied. The achievements of such alchemists as Glauber, Bottger, and Kunkel, in this direction, may be boldly compared to the greatest discoveries of our century. Many of the fundamental or leading ideas of the present time appear, to him who knows not what science has already achieved, as extravagant as the notions of the alchemists. Not, indeed, the transmutation of metals, which seemed so probable to the ancients, but far stranger things are WONDERS OF MODERN SCIENCE. 55 held by us to be attainable. We have become so accus- tomed to wonders that nothing any longer excites our astonishment. "We fix the solar rays on paper, and send our thoughts literally with the velocity of lightning to the greatest distances. We can, as it were, melt copper in cold water, and cast it into statues. We can freeze water into ice, or mercury into a solid malleable mass, in white-hot crucibles ; and we consider it quite practicable to illuminate most brightly entire cities with lamps devoid of flame or fire, and to which the air has no access. We manufacture largely, ultramarine, one of the most precious minerals ; and we believe, that to-morrow or next day some one may discover a method of producing, from a piece of charcoal, a splendid diamond ; from a bit of alum, sapphires or rubies ; or from coal-tar, the beautiful colouring principle of madder, or the valuable remedies known as quinine and morphine. All these things are either as precious or more useful than gold. Every one is occupied in the attempt to discover them, and yet this is the occupation of no individual inquirer. All are occupied with these things, inasmuch as they .study the laws of the changes and transformations to which matter is subject ; and yet no one individual is specially engaged in these researches, inasmuch as no one, for example, devotes his life and energies to the solution of the problem of making diamonds or quinine. Did such a man exist, fur- nished with the necessary knowledge, and with the courage and perseverance of the old gold-makers, he would have a good prospect of being enabled to solve such problems. The latest discoveries on the constitution and production of the organic bases permit us to believe all this, without giving to any one the right to turn us into ridicule. Science has demonstrated that man, the being who per- forms all these wonders, is formed of condensed air (or solidified and liquefied gases) ; that he lives on condensed as well as uncondensed air, and clothes himself in condensed air ; that he prepares his food by means of condensed air, and, by means of the same agent, moves the heaviest weights with the velocity of the wind. But the strangest part of the 56 LETTERS ON CHEMISTRY. matter is, that thousands of these tabernacles formed of con- densed air, and going on two legs, occasionally, and on account of the production and supply of those forms of condensed air which they require for food and clothing, or on account of their honour and power, destroy each other in pitched battles by means of condensed air : and further, that many believe the peculiar powers of the bodiless, conscious, thinking, and sensitive being, housed in this tabernacle, to be the result, simply, of its internal structure and the arrangement of its particles or atoms; while chemistry supplies the clearest proof, that, as far as concerns this the ultimate and most minute composition and structure, which is beyond the reach of our senses, man is, to all appearance, identical with the animal lowest in the scale of creation. But to return to alchemy. In judging of it, we are but too apt to forget that a science represents a spiritual or- ganism, in which, as in man, self-consciousness first appears at a certain stage of its development. We now perceive that all the special objects pursued by the alchemists have con- tributed to the attainment of a higher end than that of which they were conscious. The path which has led to this result was obviously the best. To build a palace, we require many stones which must be quarried, and many trees which must be felled and hewed ; but the plan comes from above, and is known to the architect alone. The philosopher's stone, for which the ancients sought with a dim and ill-defined impulse, was, in its perfection, nothing else than the science of chemistry. Is that not the philo- sopher's stone which promises to increase the fertility of our fields and to insure the prosperity of additional millions of mankind ? Does not chemistry promise that instead of seven grains we shall be enabled to raise eight or more on the same soil ? Is that science not the philosopher's stone which changes the ingredients of the 'crust of the earth into useful products, to be further transformed, by commerce, into gold ? Is that knowledge not the philosopher's stone which pro- mises to disclose to us the laws of life, and which must finally yield to us the means of curing diseases and of prolonging life 1 PHLOGISTIC PERIOD OF CHEMISTRY. 57 Every new discovery opens up wider and richer fields to our researches ; and in the laws of nature we are still ever seeking the " virgin earth " of the alchemist, a search which can never have an end. , Ignorance of the history of science is the cause why we frequently look back with a kind of contempt also on the second period of chemistry, namely, the phlogistic period, and regard it as insignificant. Our self-esteem deems it in- conceivable that the experiments of John Rey, on the increase of weight in metals during the operation called calcination, remained unregarded ; and that, while these experiments existed, the idea of phlogiston could be developed and obtain a footing. But all the efforts of that age were directed to the arrangement of that which was ascertained, and which waited only for arrangement. Key's observations had no influence whatever on that period, because they were not yet brought into connection with the process of combustion generally ; for there were many bodies which, by combustion, became lighter, or disappeared to the senses. The object of the labours of Becker and Stahl and their followers was the dis- covery of these phenomena which belonged to the same class and were produced by the same cause. The progress of chemistry to our time was determined by the great and incomparable discoveiy that the calcination of metals and the production of sulphuric acid from sulphur, and, on the other hand, the recovery of metals from their calces and of sulphur from sulphuric acid, were analogous processes closely related to one another. In that discoveiy lies a truth, which is still acknowledged as such, and is quite inde- pendent of the knowledge of the relative weights. Before men could begin to weigh, they needed to know what was to be weighed ; before applying weight, measure, or numbers, it was necessary to know the existence of a relation between two objects, the nature and amount of which relation was to be determined. To have discovered and established such relations, in connection with the most important of all pro- cesses, the process of combustion, this is the immortal glory of Stahl. 58 . LETTERS ON CHEMISTRY. "We value facts because of their permanence and immuta- bility, and because they supply the grounds for ideas ; but a fact acquires its true and full value only through the idea which is developed from it. Many facts were not in possession of Stahl, but the idea is his property. Cavendish and Watt both discovered the composition of water. Cavendish esta- blished the facts ; Watt, the idea. Cavendish says, " From inflammable air and dephlogisticated air water is produced." Watt says, " Water consists or is composed of inflammable air and dephlogisticated air." Between these forms of expression there is a wide distinction. The attaching too high a value to the mere facts is often a sign of want of ideas. It is not fertility, but poverty, of ideas which clothes itself with a mass of coverings of all sorts, or wears old, tattered, 'threadbare, and ill-fitting garments. There are ideas so great and vast, that even when entirely perforated, as it were, in all directions, they leave enough of matter to occupy the powers of thought of mankind for a century. Such a great vast idea was that of phlogiston. Phlogiston was originally an idea, and the question as to its material existence was void of all significance, so long as the idea was fruitful in the classification of known facts, and prepared the way for new generalisations. When men took up, in their explanation (of combustion), the notion of weight, they discovered the degree in which the process depended on a peculiar ingredient of the atmosphere ; but the pheno- menon itself was not thereby better or more completely explained than before. The proportion in wliich air, or any other body, became heavier in combustion, was not known to Stahl ; and the question, in what relation the process of decomposition, in virtue of which light and heat are developed, stands to the process of combination, or to the gain or 'loss of w r eight 1 this is a problem unsolved to the present day. The difference is, that we push aside, and in a manner neglect, the phenomenon which Stahl regarded as the chief one. That which is developed in accordance with natural laws cannot proceed faster than it actually does. It was only ANTI-PHLOGISTIC THEOEY. 59 after men had become acquainted with palpable objects, that the chemistry of invisible bodies could acquire a form. The modern idea of a chemical compound has proceeded from pneumatic chemistry ; but in Stahl's time, the notion of the chemical character of a gas or of the air was not yet de- veloped. It was on the loss of volume, or on the disappear- ance of a gas, that men first saw and recognised chemical attraction. Hales, in 1727, saw air (or gas) produced from a number of bodies by the action of heat. Everything that possessed the gaseous form and elasticity was to him simply air ; and he was not struck with the remarkable differences between carbonic acid gas, inflammable gases, and atmos- pheric air. He explained the dimunition of volume in a gas by contact with water or in combustion, not by solution or combination, but by a loss of the expansive power. The masterly researches of Black laid the foundation of the antiphlogistic chemistry. The fundamental experiment of Lavoisier, the calcination and reviving of red oxide of mercury and the absorption and re-appearance of an ingredient of the air by these processes, is only an imitation of Black's experiments on lime and the alkalies. When Black showed that quicklime exposed to the air becomes mild (or car- bonated) and increases in weight, when he proved that this increase of weight depended on the absorption of a gas (carbonic acid) from the atmosphere, which gas could be again expelled by heat, when he demonstrated that the increase of weight in the lime was equal to the weight of the absorbed gas ; then first began the epoch of quantitative research, of the use of the balance. Phlogiston lost its significance ; the idea was replaced by a firmly linked chain of facts. Many chemists, even at the present day, find it impossible to do without certain collective names, analogous to the word phlogiston, for processes which they regard as belong- ing to the same class, or determined by the ame cause. But instead of choosing for this purpose words which designate things, as w T as the custom till the end of the eighteenth century (phlogiston means, for example, fire, or 60 LETTERS ON CHEMISTRY. light, and heat), they employ, since the time of Berthollet, terms which designate what are called "forces." For ex- ample, nothing can be more opposed to the rules of philosophic research than the invention and the use of the word catalysis or catalytic force. We all know that no essential truth is expressed in that word ; but the majority of mankind, from the want of just conceptions, cannot do without it ; and the necessity for classification and connec- tion of observed facts will, even in the case of the minority, insure its acceptance and use, until the facts to which it refers shall have been duly arranged and classified. It has been said that every science must pass through three periods of development. The first is that of presenti- ment, or of faith ; the second is that of sophistry ; and the third is that of sober research. Alchemy is regarded as the religious period of the science afterwards called Chemistry. But this opinion is decidedly erroneous, as far as concerns chemistry and all the inductive sciences. To investigate the essence of a natural phenomenon, three conditions are necessary. We must first study and know the phenomenon itself, from all sides ; we must then determine in what relation it stands to other natural phenomena ; and, lastly, when we have ascertained all these relations, we have to solve the problem of measuring these relations, and the laws of mutual dependence ; that is, of expressing them in numbers.* The science of chemistry embraces all those * The phenomenon of the effervescence of limestone and of potashes with acids has been known from the earliest times ; but it was in the seventeenth century that the observation was first made, that this effervescence proceeded from the escape of a kind of air, different from common air ; that this air occurs in certain mineral waters ; that it is formed in fermen- tation, and produced also in the combustion of coal ; that animals are suffocated, and flame extinguished, in it. Centuries passed before the phenomenon of effervescence was knpwn in every point of view, and then it was discovered that the mildness and causticity of lime and of alkalies depended on the absence or presence of carbonic acid ; that the hardening of mortar was caused by an absorption of carbonic acid from the atmos- phere ; that the development of carbonic acid in the fermentation of wine and beer depended on the decomposition of sugai-, &c. At last, carbonic acid was resolved into its elements, its composition was determined, and the proportions by weight were ascertained, in which it combines with lime THE THREE PERIODS OF SCIENCE. 61 phenomena of the material world which are determined by a certain number of natural forces or causes (such as chemical attraction, heat, light, cohesion, gravitation, &c.) ; and its his- torical development exhibits three periods, corresponding to the three conditions above specified, as being essential to the full knowledge of any individual phenomenon. In the first period of chemistry, all the powers of men's minds were devoted to acquiring a knowledge of the pro- perties of bodies ; it was necessary to discover, observe, and ascertain their peculiarities. This is the alchemistical period. The second period embraces the determination of the mutual relations or connections of these properties ; and this is the period of phlogistic chemistry. In the third period, in w r hich we now are, we ascertain by weight and measure, and express in numbers, the degree in which the properties of bodies are mutually dependent. The inductive sciences begin with the substance itself; then come just ideas ; and lastly, mathematics are called in, and, with the aid of numbers, complete the work. The political history of nations, as well as the history of science, shows us, in like manner, three periods. In the first, the qualities and faculties of men are developed, in all their varieties and contrasts. Weakness submits to strength : wisdom and the gift of invention are honoured as godlike qualities ; the general conditions of the social compact are laid down in the form of commandments. All these com- mandments begin with the words " Thou shalt ; " men have duties, but no rights. In the next period are developed the relations of mutual dependence among these qualities. The contest between opposite qualities leads to the adoption of laws ; from the consciousness of that which is right, developed the sense of the possession of rights, political and social. By the union of similar rights, political powers arise. The struggle of opposite powers (such as democracy, oli- and other basic oxides of metals ; while we also became acquainted with the amount or proportion in which its gaseous state depends on heat and pressure, with its specific and latent heat, and with its properties in the liquid and solid forms. 62 LETTERS ON CHEMISTRY. garchy, and monarchy) leads to revolutions ; and revolution is the name given to those processes by which an equilibrium is disturbed or restored. In the third or last period, that amount, degree, or proportion of mutual dependence among all qualities, rights, and powers, w r hich secures to the individual, without injury to others, the fullest and freest development of all his faculties and qualities, is fixed ; and thenceforth revolutions are at an end. TEACHING OF THE DARK AGES. 63 MBK A i VIVERSIT CALIFOR^ LETTEE IV. Teaching of the Dark Ages Opposition to new ideas Columbus Coper- nicus Invention of Printing Universities founded Galileo Over- throw of Galenic Medicine Doctrines of Aristotle System of Galen Elements of the Alchemists The Universal Medicine Paracelsus Medical Chemistry. Later Medical Theories. NUMBERLESS germs of intellectual life fill the universe, but it is only in a few rare minds that these germs find a soil in which they can be developed. In these chosen minds the idea, whose origin is unknown, shows its vitality in creative acts ; in them, the mysterious laws of nature assume a form, efficient, active, and recognisable by all. It is not to the warlike deeds of mighty princes and re- nowned generals, but to the never-dying names of such men as Columbus, Copernicus, Kepler, Galileo, and ISTewton, that history refers the past progress in natural science, and the intellectual advancement of the present time. The free ex- pansion of the human intellect was arrested for a thousand years. A system of teaching, like that of the Celestial Empire, w^hich even now excites in the learned men of China a peculiar sense of pleasure in the reading of pages of mean- ingless names, had annihilated, in the school of the scholastic philosophy, all desire after the investigation of truth. Like a tree which, when checked in its growth by external impe- diments, is crippled into the strangest shapes, so did the noblest mental powers languish and become deformed in the unyielding mould of hair-splitting dialectics. Men of ac- knowledged reputation and learning wrote books and treatises .on storms, or on showers of blood, in which they discussed every thing, save only the explanation of the phenomena. Whether Adam, while yet without sin, was already ac- quainted with the "Liber Sententiarum" of Petrus Lorn- 61 LETTERS ON CHEMISTRY. bardus ?'" what was the age and dress of the angel who brought the heavenly message to the holy Virgin Mary ? whether there had existed in Paradise, before the fall, the necessary excretions of the human body? whether the angels spoke Greek or Hebrew ? how many thousand angels could stand on a needle's point without crowding 1 To these, and similar questions and researches, which in our times would be regarded as valid evidence of insanity or folly, were the most distinguished intellectual powers devoted. Ke- nowned philosophers corresponded at great length concerning the gift possessed by the Kings of France and England, of healing scrofula by the mere touch. They disputed as to whether this miraculous gift adhered to the throne or to the family. It was reckoned among the hidden forces, the exist- ence of which was sufficiently demonstrated by experience. In order 'to find the right path, the human mind requires a guide acquainted with it ; but a secret and mysterious power held the light imprisoned ; and in this intellectual darkness, no guiding star was seen. The treasure which the early times had acquired in the form of true knowledge of nature was not duly appreciated nor regarded, and thus lost its power to enrich and fertilise. Questions of physical science were decided according to the rules of the " Ars Disputandi." In renouncing the aid of experiment and observation, which alone create science, man thus banished true science. From the want of materials for the exercise of thought, men lost the habit and dexterity given by practice, of putting just questions as to the causes of things or phenomena, of observing them, and of discovering their connections by expe- riment. Such a state of matters enables us to comprehend the supremacy of astrology, of the Cabala, of chiromancy, and the belief in witches, ogres, and sorcerers. It explains how, centuries later, diseases' could be regarded as direct judgments of Heaven, or as works of the devil, and how prayers, amulets, holy water, and relics, were considered the * Died 1164, as Bishop of Park. COLUMBUS. 65 most efficient remedies. The story of the golden tooth, at the end of the sixteenth century, proves how entirely men, even in the more cultivated classes of society, had lost the power of successfully investigating the simplest phenomenon. (See Appendix.) When Columbus had to defend his views concerning the shape of the earth, and the possibility of circumnavigating it, in Salamanca, the first seat of learning of the age, before an assembly consisting of the most learned professors of astronomy, geography, and mathematics of the Spanish kingdom, along with the wisest and most respected digni- taries of the church, he appeared to the majority as a dreamer worthy of ridicule, or as an adventurer deserving of contempt. And yet never had a learned disputation a greater influ- ence on the development of human intellect than that one in the collegiate church of St. Stephen, at Salamanca. It was the dawn of a new day, the forerunner of the great victory of truth over the blind faith of the age. In these remarkable discussions mathematical demonstrations lost their validity, when they seemed to contradict passages of Holy Scripture, or the interpretations of those passages by the fathers of the church. " How could the earth be spherical, when it is said in the Psalms, that the heavens were stretched out as a garment f ' " How was it possible to regard the earth as otherwise than flat, when the sacred writer compares the heavens to a tabernacle or tent, spread out over the earth ?" " Had not Lactantius thus pronounced against the existence of antipodes 'Is there any one so mad as to believe that there are men whose feet stand opposite to ours, and who are able to walk with their legs upwards and their heads hanging down : that there is a part of the world where all things are topsy-turvy where the trees grow with their branches downwards, and where hail, snow, and rain fall upwards V " " Did not St. Augustine say, that the doc- trine of the antipodes was altogether irreconcileable with the historical foundation of the Christian faith? for whoever said that there were inhabited countries on the opposite side 66 LETTERS ON CHEMISTRY. of the earth, asserted that there existed in those countries men who were not derived from Adam ; since it was impos- sible for his progeny to pass the intervening ocean. Such an opinion must destroy our belief in the Bible, which expressly declares that all men spring from one pair of parents." " What presumption was it in a common man to believe that so great a discovery was reserved for him, after so many profound philosophers and geographers had made the shape of the earth the object of their researches, and so many good seamen had sailed over its surface for two thousand years 1 " Thus spoke the opponents of the great man. Two years later, Columbus returned from the West Indies ! The earth was small and spherical, and there were inhabited countries at the other side of it ! But not only the earth, the heavens also contradicted the doctrines of the great luminaries of the golden age of churchly wisdom. For, in consequence of the discoveries of Copernicus, the earth had ceased to be the centre of the universe. It was not only small, narrow, and spherical it was a mere point in endless space a small planet revolving round the sun. As an indescribable feeling of terror attacks him who is surprised by an earthquake, when he feels that undulating like a rolling sea, which custom and reflection have taught him to regard as the most fixed and immovable ; so did fear and doubt convulse the civilised world in consequence of the discoveries of science. The earth was no longer the centre of the system of the universe ; the vault of heaven had lost its columns the throne of God its place. There was no longer anything above nor anything below. That which faith regarded as firmly rooted was shattered ; what had been held as truth now appeared to be error. Numerous prophecies, in the first half of the sixteenth century, con- nected the discovery of the new with the destruction of the old world. They testify to the intense excitement of that age. After Columbus had deprived the ocean of its terrors, and Copernicus had taught, "that confidence in the power of INVENTION OP PRINTING. 67 knowledge, which bursts the bands of external authority, ' and only yields belief to the evidence of reason," * the courage necessary for the investigation of unknown regions of intellect awoke also in other minds. The agent was already in existence which was to propagate the mighty shock through all the regions of science. As the blood which determines all bodily action receives its motion from the impulse of the heart, so did Guttenberg's invention of printing send warmth and vigorous life to all parts of the intellectual organism now assuming its new form.t In consequence of the foundation of numerous universi- ties, J and of the diffusion of Greek learning in the west of Europe, after the conquest of Constantinople by the Turks, in 1453, the attention of men's minds was turned, in the fourteenth and fifteenth centuries, to the intellectual trea- sures bequeathed by the old Greeks and Romans. Classical antiquity, like the sun, diffused a life-awakening light. When the learned began to learn from these unapproachable models, and to form themselves upon them, their mental vision was sharpened. The study of the classics, leading to a critical testing of all traditionary learning, broke the chains of the wisdom of the schools. Men recognised in nature the inex- haustible fountain of a purer knowledge ; and nature appeared as a newly-discovered Atlantis, formerly submerged, intellec- tually, in a sea of ignorance. Luther, in his Table-talk, most aptly describes the love of nature and its study, which arose with the Reformation. " We are now in the morning dawn of the future life, for we again begin to acquire a knowledge of God's creatures which we lost through Adam's fall. Now, we look at them directly * CarriOre, in his distinguished work, ' ' The Philosophical Considera- tion of the period of the Reformation, in its relations to the present," p. 125 ; published in German by Gotta, Tubingen, 1841. t In the same year in which Columbus was born, Guttenberg invented printing by moveable types. J Oxford in 1300, Prague in 1347, Vienna in 1384, Heidelberg in 1385, Heidelberg in 1385, Cologne in 138S, Erfurt in 1392, Cracow in 1401, Wurzburg in 1406, Leipsic in 1409. Carriere, p. 116. 68 LETTERS ON CHEMISTRY. ourselves. But Erasmus asks not after this, and cares little how the fruit is formed, shaped, and made in the mother's womb. But we, by God's grace, begin to perceive His won- ders and His works, even in the little flowers, when we think how all-powerful and good God is. We do see in his creatures the power of his word how mighty that is." Nature put forth unusual powers to secure victory to reason in the contest then beginning between the intellect of Euro- pean nations, awakened to consciousness of itself, against ecclesiastical and civil tyranny against a mighty superstition which appeared impregnable. A number of the greatest men followed in uninterrupted succession, till the great work was done and its results secured. A hundred years after Copernicus, Kepler was born, and Newton saw the light in the same year in which Galileo died. The middle ages had set up, in their theological philo- sophy, a universal science, and had fortified it with the whole authority of a religious belief. An error in science was a vice ; to deviate from the established doctrine was heresy ; it was synonymous with a rejection of the Revelation from Heaven. Tortures and the stake awaited the man who thought freely, or otherwise than this philosophy taught. A century after Luther, Galileo was compelled, in the dun- geons of the Inquisition, to recant his doctrine of the earth's motion ; and the words he murmured, " E pur si muove" when he rose from his knees, clad in a bare shirt, to this day retain the idea of the irresistible force of established facts. No one can even now read his celebrated letter to Madama Christina, Granduchessa Madre, without emotion t and yet it did not convince his opponents. (See Appendix.) But all these obstacles had, in the long run, as little success in arresting the expansion and progress of science as at a later period attended a thirty years' war in the attempt to control religious opinion. 'Error is transient ; truth alone is eternal. Error is only the shadow cast by truth, when its rays are arrested on their path by human ignorance, and intellectual opacity. In that eventful age chemistry also underwent a trans- DOCTRINES OF ARISTOTLE. 69 formation. Being conjoined with medicine, chemistry ac- quired a new object, and entered on a new direction. Alchemy had forged the weapons wherewithal chemistry was to conquer, in medicine, a new region, and put an end to the thousand years' reign of the Galenic system. The great and salutary change which medicine underwent, its liberation from the fetters of authoritative belief, was the natural result of the recognition of the unattainableness and inaccuracy of all the previously received doctrines on the true nature of material objects. The new light was a trophy gained by the alchemists ; and by its aid the doctrines of the Greek philosophers, concerning the causes of natural phenomena, acquired a new form. In all ages the reflecting man endeavours to account to himself for the origin of things, and to penetrate the causes of their peculiarities. The most natural method was un- questionably that of the mathematicians, who, without external aid, study and ascertain the laws and properties of mathematical figures. This was in truth the method chosen by the Greek philosophers in order to obtain a knowledge of natural phenomena. They regarded the various and mani- fold properties of bodies as things apart, or per se, and sought, with the aid of the understanding, to combine their observations, and to discover such properties as are common to all bodies. " The origin and properties of all things," says Aristotle, " presuppose three fundamental causes. The first is matter devoid of properties (v\rj) ; the second is the cause, or causes, which give to matter its properties, and which may be col- lected in the conception of bodily form (clSos) ; the third is a cause, or causes (forces in the sense contained in the words, force or power of a remedy, nutritive force or power), which change bodies by depriving them of their properties (o-repj/o-ts-, robbery). That which precedes the change of properties in matter is the cause, or efficient cause (TO TroiW, that which works) ; and that which follows the efficient cause is the effect (TO re'Aos, the end or object)." This conception of the properties of material bodies as of 70 LETTERS ON CHEMISTRY. things, like colours, with which the painter gives to white canvas the properties of a picture, or like clothes which are- put on and off, and thus determine the aspect of the man, is the foundation stone of alchemy, and of the first scientific system of medicine. It would be difficult for the most acute intellect, without using other means than simple perception by the senses, tc- discover more than four properties which belong to all tangible material objects. To the senses of sight, taste, and smell, material bodies offer infinite varieties ; there are coloured and colourless sub- stances ; there are those which possess taste and smell ; and there are those which are inodorous and tasteless. But all bodies are either moist or dry, either warm or cold. Everything tangible possesses two of these properties ; it is either solid or fluid, and has a certain temperature. " These properties," says Aristotle, " are obviously opposed to each other ; for cold can be destroyed by heat, dryiiess by moisture. By the conjunction of two properties, not opposed to each other, for example, of dryness and cold, we see solid bodies produced ; while, by the action of heat and moisture,, they become liquid or gaseous. Hence the mutual relations of these properties are clear ; not only the form, whether solid or fluid, and the cold or warm state of bodies, but also the relative density and lightness, are determined by these fundamental properties. Cold is the cause of density, for by its action the material particles are brought into closer contact ; porosity or lightness is in like manner caused by heat. But all the other secondary properties of matter stand also in a definite relation to the four primary or fundamental properties ; for the colour, smell, taste, lustre, hardness, &c., of bodies suffer changes by the addition or subtraction of moisture, heat, dryness, or cold." " It is plain," continues Aristotle, " that all those proper- ties of tangible bodies which are perceived by the senses are dependent on these four primary properties ; for with a change in the latter all the others undergo a change likewise. It is evident that the secondary properties are determined by the DOCTBINES OF AKISTOTLE. 71 primary; and that there are "four elementary properties of matter." The justice of these abstractions, as far as they embrace those properties of matter which can be ascertained by simple perception, cannot be disputed. The difference between our present views and those of the ancients consists in this, that we regard the solid, liquid, and gaseous states as well as the temperature of matter, as being determined by two, instead of four, opposite causes. At this hour we believe that all the external physical properties of bodies are dependent on the force of cohesion and the force of heat, according to fixed relations between these opposing causes. " Among four things," says Aristotle, " there may be six combinations, two and two (pairings) ; but the pairing of two directly opposed properties, such as cold and heat, dryness and moisture, causes both to disappear. They destroy or neutralise each other, and can no longer be recognised by the senses. Consequently only four combinations are left, which correspond to the four bodies of which the earth consists. The earth proper, as the representative of solidity, is dry and cold ; water (which represents liquidity) is moist and cold ; air (representing the gaseous state) is moist and hot ; fire hot and dry. From this pairing of properties arise the four material elements ; from these four elements are Dry and Warm. FIRE. r WATER. Moist and Cold. formed all other bodies. They are contained in all ; and the varieties .and differences in the properties of other bodies depend entirely on the proportion in which the four elements 72 LETTERS ON CHEMISTRY. are combined. Whatever element predominates gives its character to the body." As may be seen from the preceding diagram, the elemen- tary bodies, taken two and two, have a primary or funda- mental property common to both members of each con- tiguous pair. It is hence evident that when, by means of cold, the elementary property of heat is withdrawn from the air (gaseous body), the air is changed into water (liquid body) ; and, in like manner, by the aid of heat, water may be changed into air, and by the aid of dryness, water converted into earth. Fire, according to Aristotle, embraces the conception of brightness and sensation; water and air that of transpa- rency ; earth that of darkness. Colours arise from the mixture of fire and earth. The transparency of rock crystal proceeds from w^ater. (The transparency of the diamond is still called, from this view of Aristotle, its water.) But the chief constituent of the eye also is water, as air is the foundation of the sense of hearing ; air and water of that of smell j while earth is the condition of the sense of touch. Taste is produced by moisture ; the more closely the par- ticles causing taste adhere to the tongue the bitterer ; the more easily they are separated from it, the salter a bod}^ appears. But when these are heated, and in turn heat the particles of the mouth, there is produced the acrid taste ; and the sour taste is observed when the particles of the body are in fermentation and effervescence. We perceive that, in all these cases, the physical pecu- liarity of those things which affect the sense, being ascer- tained with judgment arid accuracy, is regarded by Aristotle as the determining cause. That which he observed in the effect was, according to him, the cause of that effect, and the explanation of natural phenomena was nothing more than the description of their peculiarities. These doctrines of the Greek philosophers were made by Galen the foundation of the first theoretical system of medicine. GALENIC SYSTEM OF MEDICINE. 73 According to Galen, all the pails of the organised body are produced by the mixture, in different proportions, of the four elementary qualities of matter. In the blood they are equally mixed ; in mucus, water ; in the yellow bile, fire ; and in black bile, earth, predominates. The four tem- peraments depend upon the preponderance of these four cardinal juices. Health is a state of equilibrium determined by the just conformation of similar parts, that is, of organs, and by the just mixture of the elements. In disease these relations are disturbed; disease is a state of conformation or mixture opposed to the natural state. In consequence of the misproportion of the elementary qualities, the juices are found to be too hot, too cold, too moist, or too dry. When their motions are arrested, and transpiration is impeded, there occurs a corruption of the juices, and the various forms of fever are produced. The unnatural heat of fever is a result of this putrefaction. By the putrefaction of the mucous or slimy fluids, of yellow or of black bile, quotidian, tertian, quartan, and other fevers are excited. According to Galen, the efficacy of remedies depends on the fundamental qualities inherent in each ; they are hot or cold, moist or dry. A remedy, according to the amount of the fundamental quality of heat, may produce a hardly per- ceptible or a distinct warmth ; it may excite heat more or less intense ; and each quality has four similar degrees in its action. Substances of a burning taste belong to the hot, those of a cooling taste to the cold remedies. The removal of disease on the restoration of health depends, according to Galen, on the supply of the deficient quality by communication, or in a removal of that which is in excess, by means of a remedy which tends to abstract it. In this consistent system, disease and the action of remedies were reduced to a very limited number of causes. Diseases, like remedies, admitted of classification on a certain number of divisions ; and when he had ascertained the place in the arrangement to which a disease was to be referred, 74 LETTERS ON CHEMISTRY. the physician found, in the corresponding division, the appro- priate means of restoring health. He knew the origin of the disease ; and he knew why the remedy cured it. In place of the empirical art and the method of expe- rience, which had led Hippocrates of Cos to his innumerable observations and his admirable system of dietetics, there now appeared the theory, which combined, arranged, and explained these observations. The treatment of diseases followed by the great physician of Cos could be learned only by imita- tion ; the new system was infinitely better adapted for teaching, and the acquisition of medical knowledge was rendered much easier. The Greek philosophers, as well as Galen, had no concep- tion of the peculiar properties, which are brought to light when different bodies are brought into mutual contact. It is easy to perceive, that the fundamental idea of the Galenic system was quite identical with that which guided the alchemists, the idea, namely, of the possibility of transmuting the elementary bodies by the addition or sub- traction of elementary qualities. Lustre, colour, fixity in the fire, and volatility could be removed and supplied, according to the belief of those days ; they could also be exalted and diminished. Gold was the most perfect metal, to which no properties could be added, because it possessed all. Among metals, it represented the healthy human frame. " Bring to me," cries Geber, " the six lepers (silver, mercury, copper, iron, lead, and tin), that I may heal them." Brass was diseased gold, quicksilver was diseased silver ; they could be transmuted into gold, that is, healed by the medi- cine of the third or highest order. The origin of gold was regarded as analogous to the gene- ration of animals, or to the origin and growth of plants. Raymond Lully compares the production of the philosopher's stone with digestion, with the origin of the blood, and the secretion of organic juices. In the course of their labours, the alchemists had noticed certain peculiarities in the properties of bodies, which had remained unknown to the Greek philosophers, or disregarded ELEMENTS OF THE ALCHEMISTS. 75 by them ; and by degrees three new elements, the existence of which was doubted by no one, were added to the four elements of Aristotle. To the four fundamental causes of the physical properties of matter, were now added three fundamental causes of the most general chemical properties ; namely, mercury, sulphur, and salt. In the spirit of the earlier philosophy, which ascribed all causes of action not perceptible by the senses to invisible spirits, and all sensible properties to tangible and material causes, common sulphur and quicksilver were regarded at first as actual constituents 6f the metals ; certain properties were believed to be dependent on their presence, exactly as, at a more recent- period, the causticity of lime and the alkalies was ascribed to the causticum or caustic principle, the pecular smell of certain bodies to the Spiritus rector, and the acidity of the acids to a primitive or original acid. The nature of the language of ordinary life, which avoids all abstract ideas, explains why men, in the infancy of research, ascribed a certain character or certain properties of bodies to material causes. Even Lavoisier could not shake off the idea of a primitive acid. He regarded oxygen as the generator of this primitive acid ; and long after his time, many still see in hydrogen the cause which determines acidity. In the ideas of the alchemists, actual sulphur and mercury were gradually supplanted by an ideal sulphur and an ideal mercury ; things, which combined in themselves a certain number of properties. These ideal bodies, at a later period, took the form of elementary qualities. Many bodies possessed the property of being volatile with- out alteration in their other properties, when exposed to fire. They were sublimable, like arsenic, or capable of being dis- tilled like mercury. Another class of bodies was also vola- tile, but underwent a change in the fire, such as sulphur. A third class, although changed in the fire, was not volatile, but fixed, like the salts found in ashes. Sulphur, mercury (arsenic), and salt became at last, as has been stated, abstract conceptions, simple elements, in the sense of the four elements 76 LETTERS ON CHEMISTRY. of Aristotle. As we speak of the form and shape of a thought, without understanding by these figurative terms a bodily shape, so did men in those days express abstract notions by terms indicating bodily or material things, with- out understanding thereby anything more than properties. The names given to these ideal things became collective names for certain properties, and we often use similar terms at the present day, with this difference, that, to designate their immaterial nature, we add the word " force," as in the term " catalytic force." Basil Valentine says of spirit of wine : " When a rectified aqua vitee is kindled, its mercury and sulphur separate, the sulphur burns quite vividly, for it is pure fire, and the deli- cate mercury flies into the air, and returns to its original chaos." Spirits of wine was regarded as " sulphureous vegetable mercury," which only meant that it possessed inflammability and volatility. When, in the simple notions of inflammability (sulphur), fixity (salt), and volatility (mercury), men came to include the special qualities of inflammable, fixed, and volatile bodies, according as these were observed (oily, fat, earthy mercury ; oily, fat, earthy, easily or difficultly inflammable sulphur ; earthy, fusible, vitreous salt ; inflammable, fat, oily, mercu- rial earth, c.) ; then the significance of the original notion was lost. Becoming too wide and extended, it no longer included observed facts ; and when Boyle searched after the sulphur, mercury, and salt of the alchemists, these elements no longer existed. The idea was worn out. At a much later period, the notion of a suffocating property, was desig- nated by sulphureous, the combustion of a fixed body by cal- cination ; that is, these things possessed one property in com- mon with burning sulphur or with limestone (calx). Hence it is no longer possible to give a definition of the terms " acid " and " salt," which shall include all those bodies which are called acids or salts. We have acids which are tasteless, and which do not redden vegetable blues, nor neu- tralise the alkalies ; there are acids of which oxygen is an EAELY NOTIONS OF CHEMICAL ELEMENTS. 77 ingredient, and hydrogen is absent, others which contain hydrogen and no oxygen. The notion of a salt at last became so perverted, that chemists have gone so far as to exclude from the class of true salts, by their definition, common sea salt, the salt of all salts, to which all others owe their very name. We can readily see, how easily a simple, defined notion becomes undefined, by the addition of other notions. In the place of the worn-out idea, we obtain, when we begin to dis- tinguish, a number of new and more defined and separate ideas. It is even possible that the original idea, all but its name, may be lost ; and the time may come, when we shall no longer find an acid or a salt, just as we could not find the sulphur and mercury of the alchemists, when these ideas were no longer necessary to science. Formerly, their existence appeared obvious to every man ; and they were only sought for when mankind had no further occasion for them. The chemical elements of the early philosophers could not, it is obvious, be obtained in a separate form, because they were merely terms, denoting qualities alone. No one thought of obtaining them j they were regarded as constituents of all bodies. No distinction was made between organic and inorganic or mineral substances ; their differences were ascribed to the different proportions of the elements. Vinegar was classified with the mineral acids. Spirits of wine was ranked beside chloride of tin (spirit of Libavius) ; and chloride of antimony (butter of antimony) next to the butter of the cow. In the time of Geber, the chemical process was considered analogous to the organic process ; in the thirteenth century the idea arose that the vital process might be analogous to the chemical. In the earliest period it was believed that metals, like plants, were developed from a seed or germ ; at a later period the opinion prevailed, that the chemical pro- cess generated the seed. The ancients held the processes of fermentation and putrefaction to be the cause of the genera- tion of plants and animals ; while, on the contrary, some physiologists and pathologists of the present day regard the 78 LETTERS ON CHEMISTRY. development and generation of animals and plants as the cause of fermentation and putrefaction. The views and conceptions entertained of Nature can only be rendered comprehensible to the mind by means of images or notions, derived from natural science, and clothed in the language of Nature. Now if we reflect that during the thirteenth, fourteenth, and fifteenth centuries, all knowledge of Nature and of her powers was concentrated in alchemy, magic, and astrology, it is easy to see how, by degrees, alche- mistical forms of expression for terrestrial processes passed into the language of ordinary life. The phenomena of organic life, life itself, death, and resurrection, were rendered more intelligible by means of the ideas derived from alchemy ; they could only be represented scientifically by the lan- guage of science, and alchemy was science at that period. "We poor mortals," says Basil Valentine, "are, for our sins here, by means of that death which we have well deserved, pickled in the earthly, that is, the kingdom of earth, till, in process of time, we become putrid and rot, and then are once more awakened, clarified, and sublimed, by virtue of the heavenly fire and heat, even to the celestial sublimation and elevation ; for all our dross, sins, and impu- rities are sundered from us." (Kopp. ii. 236.) Luther, in his Canonica, praises alchemy, " by reason of the glorious and fair resemblances which it has to the raising of the dead ; for even as fire from each kind of thing doth extract that which is best, and doth sunder it from the bad, and thus doth carry the spirit itself upwards, so that it shall have the upper place, whereas matter, like unto a dead body, doth remain below lying on the earth, so also will God, at the last day, by his judgment, as with fire, sunder the godless and unrighteous from the righteous and godly. The righteous will ascend to heaven, but the unrighteous will abide below in hell." (Kopp. ii. 238.) In the thirteenth century arose for the first time the idea that the philosopher's stone possessed the powers of healing disease and of restoring youth. This idea was developed from the opinion that the vital process was nothing else than THE UNIVERSAL MEDICINE. 79 a chemical process. With the philosopher's stone it was pos- sible to heal metals of their maladies, to render them healthy, to convert them into gold ; and the idea that it must have a like effect on the human body naturally suggested itself. Arnold of Villanova, Raymond Lully, and Isaac Hollandus, outdo each other in their praises of its healing virtues. Hollandus, in his Opus Saturni, says : " A portion of it, the size of a grain of wheat, should be laid in wine, and then given to the patient. The action of the wine will penetrate to the heart, and spread itself through all the juices. The patient will sweat, and thereby become, not more weary, but ever stronger and more cheerful. This dose should be repeated every ninth day, when the patient shall think he is 110 longer a man, but a spirit. He shall feel as if he were nine days in Paradise, and living on its fruits." Solomon Trismosin maintains that when an old man he renewed his youth by means of a grain of the philosopher's stone. His. yellow wrinkled skin became smooth and white ; his cheeks rosy ; his grey hair black ; his back, bowed Avith age, became erect. He restored, as he asserts, perfect youthfulness to ladies ninety years of age ! When the idea that the philosopher's stone was a universal medicine had been once developed, men were led, in the most natural way, to the use of chemical preparations in medicine ; and with this began a new era in that science. If, indeed, the stone possessed in an equal degree the pro- perties of ennobling the baser metals, and of healing disease, then the diseased human body was a far more convenient means of recognising the materia prima, and of testing its gradual refinement in the course of the processes by which it was elaborated into the perfect Magisterium. For the immber of diseases which the preparation, at a given stage of its elaboration, could heal, was an infallible test of its progress towards perfection. The more diseases it cured, the nearer must it be, in its properties, to the philosopher's stone. The true and perfect stone must heal all diseases. The Pharmacopoeia of the Galenical school contained no chemical preparations, and consisted exclusively of organic 80 LETTERS ON CHEMISTRY. substances : musk, rhubarb, castoreum, camphor, tamarinds, ginger, zedoary root, and the like were the chief remedies. Pharmacy then consisted in the art of bringing these matters into the forms of syrups and electuaries ; herbs, barks, and roots, were administered in the form of decoctions or of powders. On the authority of Galen, all metallic preparations were, up to that time, banished from the Pharmacopoeia. He re- garded mercurial preparations simply as poisons. Avicenna, it is true, had ascribed to gold and silver powers of purifying the blood ; but these metals, as a general rule, were used only in the form of leaf, to cover pills ; and so late as at the end of the fifteenth century, the external use of mer- curial ointments, prepared with fat, encountered the fiercest opposition. When we consider that the views of Galen, in regard to the cause of disease and the action of remedies, were re- garded, during thirteen centuries, as impregnable truths, and had acquired the entire infallibility of the articles of a reli- gious creed, we can understand what kind of impression must have been produced on the physicians of the sixteenth cen- tury by the discovery of the truly wonderful effects of the preparations of mercury, antimony, and other metals. A whole region of new discoveries seemed to be opened up by the ideas of the alchemists, and by the use of chemical pre- parations in medicine. There was discovered, in the blood, a property belonging to alkalies ; in the gastric juice, a property belonging to acids. A contrast or opposition was noticed between these fluids, corresponding exactly to the contrasts of the Galenic qualities. When acids were brought into contact with alkalies, new bodies were formed, neither acid nor alkaline, but possessed of properties entirely changed. The so-called mild alkalies exhibited the property of effervescence with acids, and the true nature of all fermentations, which were regarded as dependent on effervescence, appeared to be thereby explained. Heat was observed to be developed in liquids by the mixture OVERTHROW OF GALENIC MEDICINE. 81 of acids with alkalies, without the observer's perceiving proper combustion to take place. This appeared to account for the heat developed in the respiratory process. How was it possible any longer to allow any validity to the theory of Galen, concerning the vital phenomena and the action of remedies, after it had been proved that all his views in regard to the metals and their preparations were entirely fallacious ; or when it had been discovered that the peculiarities of the organised body, and the effects of remedies, depended on fundamental causes, which Galen had not taken into account in his explanations, because he was not acquainted with them ? Not only those fundamental causes, which determine the physical properties, but. also the chemical properties of bodies, must now and hence- forth be taken into account in explaining organic processes. The vital phenomena and the action of medicines now, as it appeared, depended, not alone on the relative proportions of moisture and dryness, of heat and cold, but, in addition to these, on the proportions of salt, mercury, sulphur, alkali, and acid. In consequence of such new and altered ideas, the art of healing assumed a new form. If the normal chemical character of the juices was the condition which determined the healthy state, the abnormal character of these juices was of course the proximate cause of disease ; and disease could be removed by the predo- minating chemical quality of remedies, and health thus restored. In selecting remedies, then, especial attention must be paid to the chemical constitution and character of the bile, of the saliva, of the sweat, and of the urine, &c. This was a step forward of incalculable importance. The valuable dis- covery was soon made, that the chemical state of the urine stood in a definite relation of dependence to certain diseases ; and as, in the period of science now imder review, all effects were taken for the causes, the deposits formed in the urine, or the tartar, were regarded as the causes of many diseases. In the spirit and mind of Paracelsus the new ideas of 82 LETTERS ON CHEMISTRY. the times were concentrated, and assumed a definite shape ; and when, a few years after, Luther, at Wittenberg, had burned the papal bulls, Paracelsus, at Basle, following the example of the great reformer, committed to the flames the works of Galen and Avicenna, their reign came to an end. " Men," so said Paracelsus, " had abandoned nature, and given themselves up to vain dreams ; " therefore he pointed to the open book of Nature, "which God's finger hath written. No dim study-lamp, but the sun itself, shall supply us with the true light. The eyes, \vhich have pleasure in looking, they are the right professors. Nature is without guile, righteous and perfect. From book-craft and from the working of men's fancy do grow confusion and sham fights/' " Follow me ! " thus he opens his Paragranum " Follow me ! I follow you not, Avicenna, Rhases, Galen, Mesur ! Follow me ! I follow not you, ye of Paris, ye of Mont- pellier, ye of Swabia, ye of Misnia, ye of Cologne, ye of Vienna, and ye who dwell on the Danube and by the Rhine, ye isles of the sea, thou Italy, thou Dalmatia, thou Athens, thou Greek, thou Arabian, thou Israelite ! Follow me ! I follow not you ! Mine is the monarchy ! " In Paracelsus are reflected all the ideas, all the faults, all the eiTors of his time. In him a gigantic force strives against the impediment of outward fetters. He has the instinct, but not the full consciousness of the right path. He seeks it in vain in the wilderness that surrounds him } hence his contradictions and inconsistencies ; hence his internal struggles. But his word gives to the century its direction. " The true use of chemistry," he says, " is not to make gold, but to prepare medicines." By Paracelsus chemistry was taken out of the hands of the gold-makers, and brought into the service of the far more learned and cultivated physicians ; and as he and his followers prepared their own "medicines, chemical knowledge and an acquaintance with chemical operations were thence- forth regarded as among the most essential qualifications, of the physician. In the sixteenth and seventeenth centuries, the expla- PARACELSUS. 83 nation of natural phenomena continued to revolve round the idea of the existence of hidden qualities, until extended experience led to the important truth, that matter and its properties are practical!}' not separable. We cannot any longer even conceive of them as separate. Long after Paracelsus, it was belieA r ed that the chemical operation was to the medicine what the stomach (or diges- tion) is to the food from which the blood is formed. By a thrice-repeated sublimation of corrosive sublimate with metallic mercury, calomel was obtained ; a sublimation nine times repeated produced the Panacea merciirialis. The spiritualising fundamental causes of Plato, which, according to him, determined the vital actions, are combined by the followers of Paracelsus, into the arcJiceus, which is placed in the stomach, and being furnished with all the passions of the man, governs digestion, the phenomena of motion, and the moods of the mind. When we represent distinctly to ourselves the utter con- tempt with which modern medicine looks down on the views of Paracelsus and his followers, regarding their views, like the ideas of the alchemists concerning transmutation of metals, as a hallucination, and compassionating them accordingly ; and when we compare with these views the present theories of the causes of diseases, and of the method of cure, the philosopher, with all his pride in the achievements of the intellect in the regions of truth, is humbled by the daily occurrence of contradictions, which we should hold impossible if they did not actually exist. For even now the system of Galen and Paracelsus rules, as it did formerly, over the minds of most physicians; and many views remain unchanged, except in the forms of expression. The arcliceus of the sixteenth century was transformed, in the eighteenth and the beginning of the nineteenth centuries, into the vital force of the philosophers ; and it lives on to the present day in the guise of the all-determining nervous force or influence. No one can deceive himself as to the true position of theoretical medicine who remembers that in our age, in which the true principles of investigation appear 84 LETTERS ON CHEMISTRY. to shed abroad their light, clear and brilliant, like the sun, a doctrine was able to develop itself in medical science which to our posterity will appear incredible. Who can maintain that the majority of well-informed and cultivated men of our time stand on a higher level in regard to knowledge of Nature and her powers than the iatro- chemists of the sixteenth century, when he knows that hundreds of physicians, trained in our universities, regard as true, principles which defy alike all experience and sound common sense ;' that there are men who believe that the effects of medicines are due to certain forces or qualities, which, by means of grinding and shaking, can be set in motion and increased in force, and thus communicated to inert bodies ; who believe that a law of Nature, to which no exception is known, is false for medicines, since they admit that their efficacy may be increased with their dilution and with the diminution of active matter ? Truly, one is tempted to adopt the opinion that, among the sciences which have for their object a knowledge of Nature and of her forces, medicine, as an inductive science, occupies the lowest place. Just as the farmer expects wonders from a new plough, a new sowing-machine, a new manure, or a new mode of cul- tivation, although these things, without just principles, can only waste his substance, and render him poor sooner than he would have been without them, so the physician looks for the progress of his science in the improvement of its technical part. In a new medicine, a new mode of treat- ment, or in the restoration of an imaginary composition of the blood or of the urine, he seeks, not to remove the stone which impedes the progress of his vehicle, but, like the carter, to urge the horse with his heavy load when he can no longer advance over the obstacle, by the use of the whip. And when Nature helps herself, he wishes us to believe that the whip is a power and has been the means of restoring health. All these things are useful, perhaps necessary ; but they are not used in order to clear away the difficulty for .all who are to follow, but serve only to enable him to skip over it in the easiest manner in the individual case. That which MEDICAL THEORIES UNFOUNDED. 85 . most readily presents itself to the imagination is used as a bridge ; but if the philosopher gets safely across, he allows it to fall to ruins behind him, instead of giving it a secure found- ation. If he fails, the imperfection of science is blamed for his failure. The art of experimenting makes tools or instru- ments ; but it has never happened that a mass of observations has become a science by virtue of the tools or instruments. There are building materials in abundance, so as almost to cover the ground on which the edifice should stand ; but the master builders are quarrelling, and their minds are not made up as to the plan. One would have the structure of wood ; another thinks it ought to be of stone and wood ; a third, that it should consist only of stone and iron. Two of these materials should at all events be employed ; but all three, if properly combined, would yield an excellent building, were it not for the labourers, who will have it made of straw, and built in the air. It is because of this that in the course of two thousand years even the foundation has not been finished. 86 LETTERS ON CHEMISTRY. LETTER V. Chemical Combination and Decomposition Chemical Affinity Influences of Heat, Cohesion, and other forces Solubility Use of Solvents in Analysis. IN order to obtain a clear and vivid comprehension of the almost miraculous order and regularity in which bodies enter into combination with each other, we must bear in mind the meaning which the chemist attaches to the terms combination and decomposition. The rusting of iron, the bleaching of coloured stuffs when exposed to the air, the extraction of metals from their ores, the preparation of innumerable objects of industry and commerce, and of medicines, in short, all new forms or phenomena which present themselves to our senses when bodies of different properties are brought into contact \ .all, with a very few exceptions, depend upon combination or decomposition. The ultimate causes of these new forms and phenomena are chemical forces, and these differ from all other forces, inasmuch as we perceive their existence only by their manifestations when bodies come into immediate contact with each other. As long as they remain at any measurable distances these forces have no action whatever. The domain of Chemistry is confined to this class of phenomena. Gravity, the electrical and magnetic forces, and heat exercise an influence upon chemical processes ; but as powers which act at a distance, which produce motion, or change of place, in bodies, in short, as causes of natural phenomena, the determination of their nature and their laws, in the narrower sense, belongs to physics. Iron rusts when exposed to the air. Sulphur and mer- cury combine, forming cinnabar. It is the CHEMICAL FORCE which is active between a constituent of the atmosphere CHEMICAL AFFINITY. 87 (oxygen) and the particles of the iron, between the particles of tfre sulphur and the particles of the mercury, and by which the change of their properties is effected. This chemical force is the cause of the formation of a new body with altered properties, that is, of a chemical compound. We obtain, again, the mercury from cinnabar by heating- it with iron ; and we obtain metallic iron from iron-rust by heating the latter to redness with charcoal. We decompose the cinnabar by iron, and iron-rust by charcoal. The cause is, invariably, chemical force ; the result invariably rests upon the formation of a compound. The iron which sepa- rates the mercury combines with sulphur. We had sulphide of mercury, we now obtain sulphide of iron. The charcoal which reproduces metallic iron from iron-rust enters into combination with that constituent of the atmosphere (oxy- gen) which the iron had imbibed, and which has caused the rust. The infinitely numerous chemical decompositions of com- pound bodies, the separation of one of their constituents, invariably depends upon this, that a newly added substance enters into combination with the remaining constituents. It is quite evident that these substances, under the given conditions, would not experience any change of properties, unless the cause which we designate " chemical force " were active between their particles. This chemical force, or influence, has been styled affinity, in total defiance of the vernacular acceptation of the word. It is said that two substances have an affinity, when in contact with each other they exhibit the faculty of combining together. This term (affinity) is decidedly fallacious, if it be intended to convey the meaning that such substances are related to each other. Were we to place the sixty-cue known elements pro- miscuously upon a table, a child would be able to divide them, by their external appearance, into two great classes : one class, the individuals of which possess a metallic aspect ; another class, deficient in this appearance. The first comprehends the metals ; the latter class of bodies, the metalloids. 88 LETTERS OX CHEMISTRY. These principal classes, according to the similarity of several individuals in other properties, may again be divided into smaller groups, in which those most closely resembling each other shall stand together. In the very same manner compound bodies manifest similarities or dissimilarities in their properties ; and if we arrange them into families, and thus bring those together whicli originate from the same elements, it will be found that the members of one and the same family have but very little, and frequently not even the slightest, tendency to combine with each other. They are related, or, in the usual sense of the word, possess affinity, in their properties ; but they have no attraction, no affinity, in the chemical sense of that term, for each other : whilst the members of two different families, which have most dissimilar properties, have always the most powerful attraction for each other. Thus, the compounds formed by two members of the same family possess all the more apparent qualities and defects of that family in an undiminished, and frequently in an increased, degree. But if two substances of quite oppo- site families enter into alliance, a new body is invariably formed, in which we cannot recognise the original parents. Thus, iron and mercury (two metals) stand infinitely more closely related to each other, than iron and sulphur, or mercury and sulphur (a metal and a metalloid) ; in a com- pound of the two former we immediately recognise its origin ; but who, looking at cinnabar, would guess that this sub- stance contains the silver-white fluid metal and the yellow inflammable sulphur? Hence result, in the compounds themselves, various degrees of affinity, by which term we always designate the unequal tendency or faculty of their atoms to combine with each other ; and it is upon these various degrees of attraction that all decompositions depend. It has been already stated that it is indispensably neces- sary tp the manifestation of chemical affinity that the atoms of substances should be in immediate contact with each other, or at immeasurably small distances. Now every one knows the effect which heat exercises upon bodies. How- AFFINITY INFLUENCED BY HEAT. 89 ever firmly you may drive an iron nail into the wall, it Avill gradually become loose, and at last fall out. In summer the iron is more heated than during winter, it therefore expands in summer, and with great power forces wood and stone asunder, whilst in winter the iron contracts in a greater degree than stone or wood. Expansion by heat implies that the atoms of which a substance is composed separate to a certain distance from each other, and that they again approach each other through contraction by cold. Now, since a certain contiguity of atoms is a necessary con- dition for the action of chemical affinity, it is obvious, that by the mere effect of heat a number of chemical combina- tions must be resolved into their constituents; and this, indeed, always, in cases where the influence of heat causes the distance between the ultimate particles to extend beyond the sphere of their chemical attraction. This neces- sarily causes a separation. When the heat decreases, the atoms again approach each other, and at a certain point of proximity combination again ensues. We may imagine that at a temperature immeasurably high to us, substances can exist in one and the same space, without combining, although they may possess the very strongest affinity for each other, precisely because this high temperature neutralises their affinity, opposes an insurmountable resistance to its opera- tion. So, undoubtedly, the constituents of the earth, when they possessed an exceedingly high temperature, were ar- ranged in quite a different manner from that in which we find them at present. Nay, it is not impossible that they should have floated through each other, as in a chaos, and that this chaos formed itself into our present minerals and rocks only when this temperature was greatly lowered. Let us suppose all the elements composing the earth, by the influence of a great heat, to be brought into the same state in which oxygen and hydrogen gas exist at the common temperature of the atmosphere ; the earth would be an enormous ball of nothing but gases, which everywhere would uniformly mix without entering into combination ; just as is the case with oxygen and hydrogen, despite their exceed- 90 LETTERS ON CHEMISTRY. ingly great affinity. At 350 C., mercury combines with the oxygen of the atmosphere, forming a red crystalline powder, and at 400 this powder is again decomposed into oxygen gas and mercurial vapour. If we fuse a mixture of iron and lead, together with sulphur, in a crucible, the iron separates from the lead, and combines with the sulphur ; as long as there remains any trace of iron in the lead, not a particle of sulphur combines with the lead, but only with the iron. When all the iron has combined with sulphur, that sulphur which still remains free combines with the lead. Both metals have an affinity for sulphur, but the affinity of the iron is far greater than that of the lead. Hence it happens when iron is fused with sulphide of lead ore (galena) as is done largely in metallurgy, that the lead separates in a pure metallic state, whilst the iron combines with the sulphur, for which it possesses a far greater affinity than lead has. In like manner, at a red- heat, iron decomposes cinnabar, and expels the mercury by combining with the sulphur ; but in this case the affinity of iron for sulphur is not the only cause of decomposition. No one has ever seen mercury red-hot, like iron, for instance, in the smith's forge ; for, whilst iron remains compact and solid at this heat, mercury is converted into an invisible vapour ; its particles obtain by heat the property of assuming the gaseous form. Now, this property depends upon the ten- dency of the atoms of a substance to repel each other to withdraw from each other and substances retain this ten- dency in their chemical combinations. Mercury evaporates, even at the common temperature ; a drop gradually passes into the atmosphere when exposed : it requires certainly a longer time than a drop of water ; nevertheless, it will gradually disappear. Cinnabar does not evaporate at the common temperature. Tins manifestly depends upon the circumstance that the tendency of the mercury to assume an aerial state, and to separate from the sulphur, meets with resistance. This resistance is the affinity of the sulphur, which is not to be overcome at the common temperature. Now, if the cinnabar be heated to that point at which the AFFINITY INFLUENCED BY COHESION. 91 mercury assumes the gaseous state, not only does the affinity between the mercury and the sulphur become weakened, but, moreover, the tendency of the mercury to separate from the sulphur becomes strengthened. If any affinity, although only a very weak one, come at this juncture to the assistance of the heat, that, for instance, of iron for the sulphur, the sulphur separates from the mercury, which would not have happened without the concurrence of these several causes. Thus, the tendency of a substance to assume an aerial form at a certain temperature, acts an important part in all chemical processes of combination and decomposition. It modifies, increases, or diminishes the manifestations of affinity. In precisely a similar manner, cohesive attraction the power which the particles of a substance possess of maintaining their cohesion against all influences which tend to destroy it has a share in the play of the affinities. We may, by the application of heat, melt sugar and common salt, render their particles moveable in all directions, destroy and annihilate their solid state. We may do the same by means of water ; but in the water in which sugar and common salt dissolve, it is not heat, but the chemical affinity of the water, which overcomes their cohesion. A fragment of bone calcined white is insoluble in water and alkaline fluids ; the tendency of its particles to maintain their state, or, as it is termed in this case, their power of cohesion, is greater than the affinity of the fluid for them. Each constituent of bone is, however, by itself soluble in water, and both are readily soluble in a number of acid fluids, as for example, in vinegar. It is, consequently, ob- vious that if we bring the constituents of this fragment of bone (phosphoric acid and lime) into an acid fluid, we do not observe any kind of alteration to take place, because both the constituents of the bone are soluble in the acid fluid, no matter in what form they may exist. But if these constituents are brought together in solution in water, which opposes no obstacle to their combination into a solid sub- stance, we shall see the bone-earth fall to the bottom as a white powder ; a precipitate, as it is termed, being formed. 92 LETTERS ON CHEMISTRY. In this manner the chemist uses the different degrees of solubility of substances in various liquids, and their deport- ment at a high temperature, as a powerful means of separa- tion, of analysis. All minerals, without exception, may be dissolved in liquids, by a proper choice of solvents. By altering the nature of the liquid, by the addition of other matters, the chemist modifies the solubility of the con- stituents of the mineral in this liquid, and in this manner he succeeds in separating all its constituents one by one. This is one method of analysis ; the other consists in adding to the solution of a compound, consisting of five, six, or more constituents, successively, other substances, which enter into combination Avith one or other of those con- . stituents, forming insoluble compounds. This is done in a certain definite order, just as if each constituent was con- tained in a different drawer, the opening of which required a particular key appropriated to itself. CHEMICAL COMPOUNDS. 93 ITEI: LETTER VI. Chemical Equivalents Definite Proportions Multiple Proportions Method of calculating from analysis, the relative numbers of the Equiva- lents of the different Elements of a Compound. Chemical Symbols Examples Acids and Bases Chemical Formula How determined Examples. IN studying these combinations and decompositions, the question immediately arises, what is the quantity of any one given substance that is required to form a chemical com- pound with another ? or how much of a third body is required to expel one of the constituents of that compound, and to replace it by the third ? All these questions have been studied, and satisfactory answers have been returned to them, in all their various bearings. We know exactly the proportions in which bodies unite, as ' well as the proportions in which they replace each other in chemical compounds. A chemical compound is characterised by this, that the proportions by weight, of its constituents, are invariable. In this lies the distinction between such a compound and a mere mixture, in which the ingredients are present in variable and indefinite proportions. In the following lines are given the proportions, by weight, of the constituents of some chemical compounds : Water contains Hydrochloric acid Carburetted Hydrogen Oxygen . 88'89 Chlorine . 97' 76 Carbon . 85*71 Hydrogen. 11 '11 Hydrogen . 2'24 Hydrogen. 14-29 100-00 100-00 100-00 Hydrosulphuric acid Hydriodic acid Sulphur . . 94-19 Iodine . . 99'21 Hydrogen. . 5 '81 Hydrogen 0-79 100-00 100-00 01 LETTERS ON CHEMISTRY. That the constituents of a chemical compound are present in it in invariable proportions is regarded as the first and most important law of combination ; so much so, indeed, that it is impossible for us to conceive water with the same properties as ordinary water, but having a different propor- tion of hydrogen and oxygen from that above given. The observations which have led to this law belong to modern times, and it may be for this reason that, in earlier ages, when the law was unknown, chemists had- very undefined notions concerning the relation between the properties of a compound and the proportions of its constituents. We now know that the properties of a compound depend on certain definite relations of weight, and these properties alter with the increase or diminution of the proportion of a constituent. On the other hand, it must also be regarded as another important discovery, that, as experience proves, the consti- tuents of a simple chemical compound, when they enter into other chemical compounds, replace each other exactly in the proportion in which they combine. In the composition, in 100 parts, of water, hydrochloric acid, hydrosulphuric acid, given above, we learn the proportion, by weight, in which hydrogen, oxygen, chlorine, sulphur, &c., replace each other. When, therefore, in a compound of oxygen, the oxygen is removed, and hydrogen is to be substituted for it, then we find, always and invariably, 88 '89 parts by weight of oxygen replaced by 11 '11 parts by weight of hydrogen. In like manner, 2 '24 parts of hydrogen, in a compound of that body, are replaced and represented by 9 7 '7 6 parts, by weight, of chlorine ; and 94*19 parts of sulphur by 5'81 of hydrogen. The above results of decomposition, ascertained by analysis, may be expressed in a simple form. To 1 part, by weight, of hydrogen there is found In Carburettcd In water, In Hydrochloric acid, Hydrogen, 8 parts of Oxygen. 35-4 of Chlorine. 6 of Carbon. Iii 9 parts of water there is 1 of hydrogen. Now, since CHEMICAL EQUIVALENTS. 95 this 1 part of hydrogen is replaceable by 35 '4 of chlorine and 6 of carbon, it is evident that these numbers (8 oxygen, 35-4 chlorine, 6 carbon) represent also the proportions in which those bodies combine together. In 9 parts, by weight, of water, there is 1 part, by weight, of hydrogen, removable and replaceable by 354 parts of chlorine. It follows that, when this replacement has taken place, there must have been formed a compound of oxygen and chlorine, an oxide of chlorine, in which 8 parts of oxygen are united with 35 -4 parts of chlorine and so with carbon, 6 parts. 1 of Hydrogen replaced by 35 '4 Chlorine, 8 Oxygen, add Oxygen 8' (from the water), 9 "Water, we have 43 '4 Oxide of Chlorine ; and 1 Hydrogen replaced by 6 Carbon, 8 Oxygen, add 8 Oxygen (from the water), 9 Water, we have 14 Carbonic Oxide. Further : since 1 part of hydrogen is replaceable by 35-4 of chlorine, it follows, that if we replace the hydrogen in 7 parts of carburetted hydrogen (containing 1 of hydrogen) by chlorine, then 6 parts of carbon unite with 35*4 of chlorine. 1 Hydrogen replaced by 35'4 Chlorine, 6 Carbon, add 6* Carbon (from the Garb. Hyd.) 7 Garb. Hydrogen. we have 41 '4 Chloride of Carbon. We see, then, that 8 parts, by weight, of oxygen, 354 of chlorine, and 6 of carbon, express actually, not only the pro- portions in which all these bodies unite with 1 part of hydrogen, but also the proportions in which they combine among themselves ; for replacement, in fact, means nothing else than combination. This law of replacement or combination in definite and invariable proportions is true not only for the bodies just named, but for all. * If, therefore, we know the proportions, 96 LETTERS ON CHEMLSTIIY. by weight, in which one body combines with another, or with ten others, or with twenty, or with all other bodies, we know also the proportions, by weight, in which all these bodies mutually replace each other ; that is, in which they combine among each other, one with another. The following Table scarcely requires, after these remarks, any explanation : Oxygen Hydrogen Carbon . Sulphur Nitrogen Phosphorus 8 Potassium (kalium) . K 39 '2 H 1 Calcium . . . Ca 20 "0 C 6 Silicon. . . . Si. 14 -8 S 16 Lead (plumbum) . Pb 103'8 N 14 Copper (cuprum) . . Cu 31*8 P 32 Quicksilver (hydrargyrum) Hg 100 '0 These numbers express the proportions, by weight, in which a few simple substances combine with each other j or, in other words, they are the equivalent amounts in which they replace each other in their combinations. Further, it must be especially remarked that these rela- tive numbers do not change, even in those cases in which one body forms, with a second or with a third, more than one compound. Thus, for instance, 14 parts of nitrogen combine with 8 parts of oxygen, and form the substance known as the laughing gas, nitrous oxide. There exists another compound of these substances, also a colourless gas (nitric oxide), which forms red fumes when it comes into contact with atmospheric air, and which to 14 parts of nitrogen contains twice 8 = 16 parts of oxygen. A third compound contains 3 times 8 = 24 parts of oxygen, with 14 of nitrogen (nitrom acid]. A fourth contains 4 times 8 = 32 parts of oxygen to the 14 of nitrogen (kyponitric acid). A fifth (nitric acid) contains 5 times 8 = 40 of oxygen, invariably, to 14 parts of nitrogen. I may adduce another example in the compounds of carbon and oxygen. Carbon combines with oxygen in two proportions : the first compound, an inflammable gas (carbonic oxide), contains COMBINING PROPORTIONS. 97 8 parts of oxygen to 6 parts of carbon ; the other (carbonic acid) contains twice 8 = 16 oxygen to 6 of carbon. These fixed and invariable proportions are observed in all cases where the elementary bodies unite to form any definite compound. Again, from the analysis of acetic acid, it appears that this acid contains in 100 parts, by weight, 47'06 carbon, 5-88 hydrogen, and 47*06 oxygen. These numbers in 100 parts inform us how much oxygen and hydrogen are com- bined with 47 "06 of carbon ; and nothing is easier than the calculation for finding how much oxygen and hydrogen is in this substance combined with 6 carbon. This is a simple rule-of-three question. To 6 carbon we have in acetic acid | hydrogen and 6 of oxygen ; or, to express the same in whole numbers, let us multiply by 4, and we then have 24 carbon, i.e., 4 times 6 ; 3 hydrogen, i.e., 4 times f ; and 24 oxygen = 4 times 6. Or, to look at it in another point of view, we know how much carbon and hydrogen are in acetic acid combined with 47 '06 of oxygen, and we may calculate how much of these two elements are united with 8 of oxygen (that is, with another of these invariable numbers representing the simple elements) ; and we obtain as the result, to 8 oxygen, 1 hydrogen and 8 carbon ; and this, multiplied by 3, gives us precisely the same proportions. The composition of all chemical compounds whatever may be expressed in the same manner, by invariable numbers, which on this account have been designated by the term combining proportions, and, with respect to their mutual power of substitution, equivalents ; because, indeed, they express the quantities in which substances enter into admix- ture, or rather into chemical combination, or in which they produce equivalent effects. Or, to state this in other words, if, in order to exercise any chemical action, we require for any given purpose 8 parts of oxygen, and if, instead of the oxygen, we are able and desire to employ for the same pur- pose sulphur, we invariably require 16 parts of the latter body. Thus these combining proportions are the represent- ation of equal values of effect. Hence the term equivalent. 98 LETTERS ON CHEMISTRY. The establishment of the truth of the great natural law, that all bodies capable of entering into combination always do so in definite and fixed proportions, led chemists imme- diately to the invention of symbolical language, which enables them to express, in an exceedingly simple manner, the constitution of every compound body, the replacement of any of its elements, and, in general, the mode in which the constituents are supposed to be arranged in eveiy compound. In the first place, chemists have agreed to designate the elements, and at the same time their equivalents, by the initial letter of the names of the elements in the Latin language. Thus, the letter 0, for example (from oxygenium) in the symbolic language of chemistry, signifies not merely the element, oxygen, but neither more nor less than 8 parts by weight of oxygen. H represents 1 part by weight of hydrogen ; S, 1 6 parts by weight of sulphur. The vast advantages of this system are abundantly obvious. The most retentive memory would not be able to retain with accuracy and permanently the proportions, in 100 parts, of the constituents of fifty compound bodies, whilst by the use of symbols and formulae nothing is easier of apprehension and recollection; thus, the composition of water, which, stated according to the per-centage of its elements, is com- posed of 88-89 of oxygen, and 11 -11 of hydrogen, is expressed by the chemist by the letters H ; the double amount by 2 H ; the threefold amount by 3 H 0, and so on. Carbonic oxide, which, as we have stated above, is com- posed of 6 carbon and 8 oxygen, is expressed by C 0. Carbonic acid, is 6 carbon, 16 oxygen, and is, therefore, written C0 2 . Acetic acid is C 4 H 3 3 ; and the combination of acetic acid and water is represented by the formula, C 4 H 3 3 + HO. Ether is represented by C 4 H 5 0; and Alcohol by C 4 H 5 + H 0. Among compound bodies we find many groups, the indi- ACIDS, BASES, AND SALTS. 99 vidual members of which exhibit similar properties, or analogous chemical relations and characters, and may be made to take each other's place, or function, in compounds. Every one is acquainted with the general properties of that group of substances which bears the name of ACIDS. The term base is, perhaps, not so universally understood. We designate compounds possessing the power of combining with acids and neutralising their acid properties, by the word BASES. A. compound of an acid with a base is denominated a SALT (this name has no reference to the taste). Now, in these compounds in salts one base may be made to replace another base, one acid another acid. Many metallic oxides, or compounds of oxygen with metals, are such bases ; and it has been observed, from a minute examination of the pro- portions in which these metallic oxides replace each other, that very unequal weights of different bases are required in this substitution. In order to expel 10 parts of one base, 15 parts of another base, or 25 parts of a third base, and so on, are necessary. If the 10 parts of the first base contain 5 parts of oxygen, we find that the 15 parts of the second, or 25 of the third base, &c., will also contain neither more nor less than 5 parts of oxygen. The amount of oxygen in the metallic bases replaced by each other, remains invariably the same ; the metals alone combined with this oxygen vary in their proportions : they replace each other according to their equivalents, that is, for 3 9 '2 of potassium, expelled from a compound, 100-0 of mercury are substituted. Chemists have agreed to designate every quantity of a metallic oxide containing 8 parts by weight, that is, one equivalent, of oxygen, as one equivalent of metallic oxide, without regard to the amount of metal it may contain. If, therefore, we once know the amount of an acid which is required to form a neutral salt with one equivalent of a base, this amount of acid remains invariably the same for an equivalent of any other base, since the other bases contain exactly the same amount of oxygen as the first, and since their mutual substitution depends exclusively upon the relative proportion of the oxygen. Chemists have also H 2 100 LETTERS ON CHEMISTRY. agreed to call that amount of acid required for the saturation of one equivalent of a base, one equivalent of add. When we are familiar with these facts, we can readily understand why chemists express the composition of acetic acid by the formula C 4 H 3 3 , and not by C 2 HIJ 0,j, or by any other. If we sum up the numbers indicated by these symbols (C 4 = 4 x 6 = 24 carbon; H 3 = 3 hydrogen; 3 = 3x8 zr 24 oxygen), we obtain as the result a total of 51. These 51 parts of acetic acid form the proportional amount (or one equivalent) of that acid which combines with one equivalent of any metallic oxide to form a salt. The formula of an acid generally refers to one equivalent of a base ; the formula of any other compound invariably refers to the relative proportions in which its elements have been found to combine with the ascertained equivalent of some other substance. In many cases, however, where this is unknown, the formulae express only the mutual relation of the composition of two or of more substances. The formula of a salt of acetic acid will consequently have to be written thus; C 4 H 3 3 , MO (M stands for 1 equivalent of any metal). If we suppose that metal to be replaced by hydro- gen, the formula will then represent a compound of acetic acid with oxide of hydrogen (water), and this, like all similar compounds of water, is called a hydrate. Its formula is C 4 H 3 3 ,.H 0, or, adding all the elements together, C 4 H 4 4 . We can also represent the salt according to the TT \ last formula, thus : C 3 ! 4 ; which represents hydrated acetic acid, in which 1 equivalent of hydrogen has been re- placed by 1 equivalent of metal. This symbolical language is of inestimable value for the comparison of the composition of various chemical com- pounds, and for facilitating the comprehension and expression of the alterations, transmutations, and decompositions which such bodies undergo. For instance, suppose I have made an analysis of acetic acid, and I am desirous to ascertain whether the numbers obtained by experiment are correct or not. For this purpose CHEMICAL FORMULAE. 101 I express the amounts of carbon, oxygen, and hydrogen, which I have found, in equivalents. These have been deter- mined with the utmost accuracy, and the nearer my numbers agree with them (this is called agreeing with the calculated result), the greater confidence I have in my analyses. If my numbers differ to any considerable degree from the equivalent numbers, I am assured there has been an error somewhere in my processes, and I have to begin my labour over again. Thus, possessing the chemical equivalent numbers of all elementary bodies, we are able to exercise a strict control over chemical analyses ; the comparison of the number shows us, that we must have fallen into some error, or that the substance under investigation does not possess the necessary degree of purity. Every one will be able to understand the following C w H 6 2 oil of bitter almonds. C 14 H 6 4 benzoic acid. Now, the oil of bitter almonds when exposed for some time to the atmosphere, absorbs oxygen, and becomes con- verted into benzoic acid. The formulee exhibit the relation between these two substances, and when translated into the numerical values, indicate exactly the quantitative change in this conversion. Again, C 4 H 6 2 is alcohol. V*] Alcohol is changed into acetic acid by the absorption of oxygen. But it is easy to see, by the formulae, that the change really consists in this, that 2 equivalents of hydrogen in the alcohol have been expelled and replaced by 2 equi- valents of oxygen. All this is exceedingly simple ; and it will now, I trust, be easy for the reader to understand what was hinted in a former chapter, that whenever a new metal or metalloid is discovered, it is sufficient to determine how much metal will combine with 8 parts by weight of oxygen, or how much of the metalloid unites with 39-2 of potassium, to learn at once in what proportion it will combine with all 102 LETTERS ON CHEMISTRY. other bodies ; that is, ^vhat is its equivalent number. It is precisely thus that the equivalents of lantanium and didy- mium (two new metals discovered recently in the ores of cerium), and of bromine (a new metalloid, found a few years since in sea-water), have been determined. The creative fancy or imagination has no share whatever in these facts, or in the mutual relation of bodies, which I have here explained. Every number is the result of a large series of carefully performed analyses. But the facts, or the analyses upon which they are based, have not of themselves formed, or evolved, the great natural law which they repre- sent and establish. The discovery of that law must be attributed to the sagacity and acuteness of a German chemist, and the name of BICHTER will remain as imperish- able as the science itself. ATOMIC THEORY. 103 LETTER VII. Cause of definite proportions Atomic Theory Definition of Physical and Chemical Atoms, practically indivisible by mechanical and chemical means respectively. Compound Atoms or Molecules Atomic Weights Distinction between the facts and the hypothesis. IT is easy to understand that the question as to the why ? as to the cause of these fixed invariable weights in chemical compounds, must necessarily have occupied the attention of chemists. There must certainly be some cause which renders impossible the combination of elements in any other than certain definite proportions, something which opposes an invincible obstacle to any diminution or augmentation of these relative proportions. The fixed and invariable amounts of the combining pro- portions or equivalents of bodies are the manifestations of this hidden cause, but these manifestations form the limit of the domain of true experimental investigation ; the cause itself is beyond our powers of perception, our sphere of research, and can only be a subject for the exercise of speculation for the exercise of the reflective intellectual faculties. In endeavouring to develope the theory which at present prevails, respecting the cause of the unchangeableness of chemical proportions, let it not be forgotten, that its truth or falsehood has nothing whatever to do with the natural law itself. The latter is the expression of universal expe- rience ; it remains true, invariably and immutably, however our notions respecting its cause may, from time to time, vary and change. A very ancient opinion respecting the nature of matter, well known as the theory of atoms, is, in truth, exceedingly well adapted to render the law of definite proportions intelligible to our understanding. !04 LETTERS ON CHEMISTRY. The atomic theory supposes that the space occupied by a solid, fluid, or aeriform body, is not in every part filled with matter ; but that every such substance has pores, or inter- stices, between its particles of solid matter, which pores are not like those of a piece of wood, visible, but are of an infinitely smaller size. According to this view all bodies consist of exceedingly minute particles placed at a certain distance from each other, so that there exists between every two particles, or, rather, around every individual particle, a space not filled with the matter composing the substance itself. It must be admitted that this view of the nature of matter is highly probable. We can compress a volume of air into a space a thousand times smaller than it originally occupied, and even fluid and solid substances are capable of being compressed, by mechanical pressure, into less space than they fill under ordinary circumstances. A billiard- ball thrown with considerable force upon a hard substance becomes flattened, and, after rebounding, resumes its spherical form. All bodies expand and fill a larger space when heated, and contract into a smaller space when exposed to a low temperature. All these well-known facts manifestly prove that the space which a body occupies at any given time depends upon accidental circumstances; that this space varies by the operation of such causes as temperature and pressure, which tend to render it greater or smaller. Now, when we reflect that the place within any body, occupied by one of its smallest particles, cannot at the same time be occupied by a second and a third particle, we cannot help drawing the conclusion that the augmentation or diminution of its volume, which we have described, is a consequence of a greater or less distance between its space-filling particles. Thus, in a pound of liquid water, the particles of the water must evidently be nearer to each other than they are in a pound of steam, which occupies a space 1700 times greater than a pound of liquid water. This theory affords us an intelligible insight into a number PHYSICAL AND CHEMICAL ATOMS. 105 of phenomena, which, although simple in themselves, have hitherto been altogether inexplicable upon any other suppo- sition. Again, the atomic theory presuppose^ that the small particles composing the mass of any substance are incapable of further division, that they are indivisible particles or atoms, a term applied to the ultimate particles of bodies, derived from the Greek, a, not, and Tep.v LETTER XYI. Chemical Attraction forms the substance of organised bodies Influence upon it of Light, Heat, Cohesion, Gravity, and the Vital Force Action of Heat, both on Inorganic and Organic Bodies Disturbance of Equili- brium Direction of Attraction Organic Atoms or Molecules No ele- ment, as such, can serve as food for a plant or animal. NEITHER heat, electricity, nor the vital force, are capable of connecting the particles of two dissimilar elements into a group, of uniting them into a compound; this, the chemical force alone is able to accomplish. Everywhere in organic nature, in all combinations which are produced in the living animal or vegetable organisms, we meet with the same laws, we find the same fixed and immutable combining proportions, as in organic nature. The substance of brain, of muscle, the constituents of blood, of milk, of bile, &c., are compound atoms, the formation and duration of which depend upon the affinity which acts between their ultimate particles, their compo- nent elements. It is affinity, and no other power, which causes their aggregation. Separated from the living body, withdrawn from the influence of the vital force,* it is the chemical forces alone which determine the conditions of their ulterior existence. Upon these depend, according to their energy and direction, the strength or weakness of the resistance which they oppose to external causes of perturba- * The term " vital force," in the present state of science, does not denote a force, per se, as we may suppose the terms electricity or magnetism to do ; but it is a collective term, embracing all those causes on which the vital properties depend. In this sense it is as just, and may be used with as much propriety, and convey a similar meaning to the term "force of affinity," or " chemical force," which denotes the causes of chemical phenomena ; of which we know quite as little as we do of the cause or causes which determine vital phenomena. o 194 LETTERS ON CHEMISTRY. tion, to forces tending to annihilate the chemical attraction existing between their component elements. But LIGHT, HEAT, the VITAL FORCE, the FORCE OF COHESION, and the FORCE OF GRAVITY, exercise a most decided influence upon the number of the simple atoms which unite to form a compound atom, and upon the manner of their arrangement. They determine the form, the properties, the characteristic qualities of the combinations, precisely because they are able to communicate motion to atoms at rest, and to annihilate motion by resistance. Light, heat, the vital force, the electric and magnetic forces, the power of gravity, manifest themselves as forces of motion and of resistance, and as such, change the direction, and vary the strength, of the chemical force ; they are capable of elevating this force, of diminishing, or even of annihilating it. Mere mechanical motion suffices to impart a definite direction to the cohesive attraction of crystallising substances, and to modify the force of affinity in chemical combinations. We may lower the temperature of water, when completely at rest, far below the freezing-point, without causing it to crystallise. When in this state, the mere touch with a needle's point suffices to convert the whole mass into ice in a moment. In order to form crystals, the smallest particles of bodies must be in a state of motion ; they must change their place, or position, to be able to arrange themselves in the direction of their most powerful attraction. Many hot, saturated saline solutions deposit no crystals on cooling, when completely at rest ; the smallest particle of dust, or a grain of sand, thrown into the solution suffices to induce crystallisation. The motion once imparted propagates itself. The atom to which motion has just been communicated imparts the same impulse to the next, and in this way the motion spreads throughout all the atoms of the mass. When we bring metallic mercury into a solution of sulphuret of potassium, its surface becomes immediately covered with black amorphous sulphide of mercury, and as often as this film is removed from the surface it is renewed. ACTION OF PHYSICAL FORCES. 195 If we place this mixture in a well-closed glass bottle, and attach this bottle to the frame of a saw in a saw-mill, which moves up and down several thousand times in an hour, the black powder becomes converted into the finest red cinnabar, the constitution of which differs from the black sulphide only by its crystalline character. The common cast-iron of commerce owes its hardness, brittleness, and crystalline texture to its containing carbon ; pure iron, free from carbon, is but very rarely crystalline. The iron of meteoric stones differs from cast-iron inasmuch as it possesses, with a most decided crystalline texture, the greatest malleability, like a very pure wrought iron. But a bar of wrought iron is tough in breaking, and fibrous, showing no crystalline texture in its fracture. Its smallest particles are intermixed without any order or arrangement ; when it is polished, and its surface moistened with an acid, it does not exhibit the characteristic lines and markings of crystalline iron. But if this bar be exposed for a long time to feeble, but constantly repeated, strokes of a hammer, its atoms will be found to alter their position, and, through the influence of the mechanical motion imparted to them, they will arrange themselves in the direction of their most powerful attraction ; the bar will become crystalline and brittle, like cast iron, the fracture being no longer fibrous, but smooth and shining. This phenomenon is manifested more or less speedily in the iron axles of locomotive engines and travelling carriages, and becomes the cause of accidents which cannot be foreseen. But it is not only upon the external form and character, and upon the arrangement of homogeneous particles, that me- chanical forces have a determining influence, but also upon the manner of arrangement of heterogeneous atoms, that is, upon the existence of chemical combinations. The faintest friction, the slightest blow, causes fulminating mercury and fulminating silver to explode ; the mere touch with a feather suffices to decompose the ammoniacal oxide of silver, or the iodide of nitrogen. The mere putting the atoms into motion in these instances alters the direction of the chemical attraction. o 2 196 LETTERS ON CHEMISTRY. Owing to the motion imparted, the atoms arrange themselves into new groups. Their elements aggregate anew, forming new products. Far more frequent and evident still is the influence which heat execises upon the manifestation of affinity. Inasmuch as it overcomes resistances which oppose themselves to the action of affinity, it promotes and effects the formation of chemical combinations. When heat opposes, as a resisting power, the force of affinity, it alters the direction of attraction, the arrangement of atoms,- it prevents or annihilates the exercise of the affinity. The attraction which dissimilar atoms have for each other, at lower degrees of heat, or lower temperatures, is different from that which they have at a higher temperature. In the highest conceivable degrees of heat, chemical combinations no longer take place. When a solution of common culinary salt in water is exposed to a very low temperature, the salt crystallises in fine, large, transparent, and pellucid prisms, which contain 38 per cent, and upwards of water in chemical combination, whilst the crystals of the same salt formed at common temperatures are always anhydrous. Upon the slightest touch the hydrated crystals lose their transparency, and assume a milky appearance ; if placed in the palm of the hand they deliquesce, and are converted into a mass of small cubes of anhydrous common salt. At 10 C. (14 F.) the atoms of salt enter into combination with water, but at C. (32 F.) the attraction between them ceases. The small difference of 18 F., is, as a resistance to affinity, sufficient to counteract its effects. When carbonate of lime crystallises from its solution in cold water, its particles arrange themselves into the form of the Iceland or doubly refracting spar ; when from hot water, we obtain it in the form of arragonite. Both these minerals, although so diverse in their crystalline forms, so different in hardness, specific gravity, and power of refracting light, contain, nevertheless, absolutely the same proportional amounts of carbonic acid and of lime. We see in this instance that particles of carbonate of lime, HEAT MODIFIES CHEMICAL FORCES. 197 in becoming solid under the influence of different tem- peratures, form themselves into substances physically quite different. And it is even still more remarkable that, if we expose a crystal of arragonite to a feeble red-heat, that is, to a heat of a higher degree than that at which it was formed, a commotion or movement takes place throughout the whole mass of the crystal, and without the slightest alteration occurring in its weight, the entire crystal swells up, presenting the appearance of a cauliflower, and becomes converted into a heap of powder composed of minute crystals, each of which exhibits the rhombohedral form of common calcareous spar. The interior of a hen's egg undergoes, by the influence of a temperature of 167 F., a complete alteration in all its properties. The fluid albumen which, in its natural state^ is nearly colourless, presenting only a very feeble yellow tint, assumes a white appearance like porcelain, and its particles lose entirely their mobility. We see that this most remarkable change takes place without the addition of anything material, and without the withdrawal of any substance whatever. Previous to the application of heat, the particles of the albumen admitted of their being inter- mixed with water in every proportion they were soluble ; but, in consequence of the motion imparted to them by heat, they have lost this property j their constituent atoms have grouped themselves into a new form ; and it is the new manner of their atomic arrangement which causes this alteration in the properties of the albumen. The chemical forces which were active between the particles of albumen, constitute the ultimate cause of this new mode of arrange- ment, of these new physical properties. In this newly- acquired form they manifest a resistance to disturbing forces, of which they were originally devoid ; they oppose the influence of heat, as they were not before capable of doing. All organic substances exhibit similar phenomena j they all, without exception, are mutable and destructible by the influence of a more or less elevated temperature ; the resist- ance which their atoms that is, the forces active in them, 193 LETTERS ON CHEMISTRY. oppose to the disturbing causes, being invariably manifested in a new manner of arrangement. From a compound atom, one, two, or three new groups of atoms are formed in such order that a state of equilibrium is invariably restored. The power of resistance to disturbing forces, that is, chemical force, is stronger in the newly-formed products than in the original substance, but the sum total of the power of affinity does not increase, it only becomes stronger or more intense in a certain direction. What we mean by the direction of the force will be rendered more intelligible by contemplating the state of a particle of water in the centre of a mass of water, as, for instance, in a filled glass. The particle of water in the centre of the glass is attracted by all the surrounding particles in its immediate vicinity, and it exercises the same degree of attraction towards them, and equally on all sides. The mobility of the particle of water, and the facility of its displacement, depend upon the circumstance that all the attracting forces acting upon it are in a state of equilibrium. The application of the slightest external mechanical force suffices to remove it from its place ; the least difference in the temperature, increasing or diminishing its density, causes a change in the position of the particle. If it were attracted more powerfully from one side than another, it would tend towards the direction of the most powerful attraction ; a certain amount of force would be required to divert it from that direction. The particles of the water upon the surface are precisely in this state ; they are less mobile than the particles of the inferior layers, or those below the surface ; they are more closely connected with each other, denser, in a more contracted state, as if influenced by external pressure. With a certain degree of caution, a fine steel needle may be maintained swimming upon" the surface of water, whilst, if submerged in the water, it instantly sinks to the bottom. This more powerful cohesion of the particles of water at the surface, arises from the particles attracting and being- attracted only in one direction. The attracting force from DIRECTION OF ATTRACTION. 199 below is not opposed by any attraction from above. To enable a steel needle to fall to the bottom of a vessel of water, the particles on the surface must first give way, must be displaced, but they do not yield thus, although the needle presses upon them with a weight from seven to eight times greater than that of an equal volume of water. The attracting force which maintains the connection of constituents in chemical combination, acts in precisely the same manner. The directions of the attractive force become multiplied with the number of elements, with the number of atoms united into a group. The force of the attraction diminishes in the same proportion as the number of directions increases. Two atoms united into, a compound can only attract each other in one direction ; the entire amount, the sum total of their attracting force, manifests itself in this single direc- tion. If a second and a third atom be added to the group, part of the force will be required to attract and retain these atoms also. The natural consequence of this is, that the attraction of all the atoms for each other becomes weaker, and they, therefore, oppose a less powerful resistance than the first two atoms previously opposed to external causes tending to displace them. The great and most marked distinction between organic and inorganic bodies lies in the former being combinations of higher or more complex orders. Although organic sub- stances are composed of but three, four, or, at most, five elements, their atoms are, nevertheless, far more complex than those of mineral substances. For example, a particle of common salt, or of cinnabar, presents a group of not more than two atoms, whilst an atom of sugar contains thirty-six elementary atoms, and the smallest particle of olive-oil consists of several hundred simple atoms. In the common salt, the affinity or attraction is exerted only in one direction ; in the atom of sugar, on the contrary, it is acting in thirty-six different directions. Without adding or withdrawing any element, we may conceive the 200 LETTERS ON CHEMISTRY. thirty-six simple atoms, of which the atom of sugar consists, to be arranged in a thousand different ways ; with every alteration in the position of any single atom 'of the thirty- six, the compound atom ceases to be an atom of sugar, since the properties belonging to it change with every alteration in the manner of the arrangement of its constituent atoms. It is evident that impulses of motion, certain causes tending to disturb the force of affinity, which exercise no decomposing influence upon more simply constituted atoms, as, for instance, those of inorganic substances, may, nevertheless, be capable of producing alterations in organic atoms ; that is, in all atoms of a higher order. It is upon the greater complexity of composition of organic bodies, together with the lesser force with which, conse- quently, their constituent atoms attract each other, that their easier decomposability depends ; heat, for example, disturbs their composition with much greater facility than it does that of inorganic bodies. The atoms of the former, once put into motion, or by the action of heat being separated to a greater distance from each other, arrange themselves into less complex atoms, in which the force of attraction acts in fewer directions, and in which it is con- sequently able to oppose a proportionally stronger resistance to the further action of causes of disturbance, of decom- position. All minerals, or inorganic compounds, are formed by the free and unfettered action of chemical affinity; but the mode and manner of their aggregation, the arrangement of their particles, depend upon the co-operation of external and extraneous causes; these latter causes determine the form and the physical properties of the compound. If, for exam- ple, the temperature had been higher or lower, whilst the atoms of a compound substance were combining, they would have arranged themselves into -quite different groups. Precisely in the same manner as heat influences inorganic combinations, heat, light, and above all, the vital force, are the determining causes of the form and properties of com- pounds produced in living organisms ; these causes determine ORGANIC ATOMS. 201 the number of atoms and the mode ' and manner of their arrangement. We are able to construct a crystal of alum from its ele- ments, namely, sulphur, oxygen, hydrogen, potassium, and aluminum, inasmuch as heat as well as chemical affinity are, within a certain limit, at our free disposal, and thus we can determine the manner of arrangement of the simple and compound elements. But we cannot make a granule of starch from its elements, because in their aggregation into the cha- racteristic form of starch granule the vital force co-operates, which is not within the reach of our control, as heat, light, the force of gravity, &c., are to a certain extent. But when the elements have once aggregated into organic atoms in the living organisms, they come under the same category with all other chemical compounds ; we are able to guide, in vatibus and manifold directions, the force which is active among these atoms, maintaining them in connection ; we are able to alter this force, to increase or to annihilate it. We may pro- duce atoms of a higher order by combining together two, three, four, or more compound organic atoms ; we can decom- pose the more complex into less complex compound atoms ; we can produce sugar from wood and from starch, and from sugar we can produce oxalic acid, lactic acid, butyric acid, acetic acid, aldehyde, alcohol, formic acid, &c., although we are altogether incapable of producing any of these compounds by direct combination of their elements. The vital force has not the slightest influence upon the combination of the simple elements, as such, into chemical compounds. No element, by itself, is capable of serving for the nutrition and development of any part of an animal or vegetable organism. All those substances which take a part in the processes of life are inferior groups of simple atoms, which, under the influence of the vital force, combine into atoms of a higher order. The chemical force, under the dominion of heat, determines the form and properties of all the more simple groups of atoms, whilst the vital force deter- mines the form and the properties of the higher order of atoms, that is, of organic atoms. 202 LETTERS ON CHEMISTRY, LETTER XYIL Origin of Organic Atoms ; from Carbonic Acid, Water, and Ammonia Derivation of non-azotised Vegetable Products from Carbonic Acid and Water by Deoxidation Coupled Compounds Decay of Organic Bodies, caused by the action of Oxygen, as seen in cut fruit Putrefaction and Fermentation denned and described Vinous Fermentation of Sugar Heat modifies Fermentation Ferments Flavour of Wines and Spirits. THE carbon of all parts and constituents of vegetables, and, through vegetables, of animals, is derived from carbonic acid ; all the hydrogen of non-nitrogenised organic bodies (sugar, starch, woody fibre, gum, oils, &c.) is derived from water ; and all the nitrogen of nitrogenised organic bodies is obtained from ammonia. An atom of carbonic acid is a group of three elementary atoms, of which one is a carbon atom, and two are oxygen atoms. No part of a vegetable or animal organism contains, for one atom of carbon, more than two atoms of another element. The great majority of organic bodies contain, for one atom of carbon, less than two other atoms. All constituents of organisms are formed of atoms of car- bonic acid, more or less modified, or of groups of such modi- fied carbonic acid atoms. These atoms and groups of atoms have been produced, under the influence of solar light, from the carbonic acid absorbed by the roots and leaves of plants. The change is the result of a separation and extrusion of part of the oxygen of the carbonic acid atoms, in the place of which oxygen there is taken up hydrogen, or hydrogen and nitrogen. Viewed in the simplest way, an atom of grape- sugar, for example, may be regarded as an atom of carbonic acid,* in which one oxygen atom has been removed and * The formula of carbonic acid is C0 2 ; that of grape-sugar may be ORIGIN OF ORGANIC ATOMS. 203 'replaced by one hydrogen atom ; and cane sugar, gum, starch, and the substance of woody cells (cellulose), as consisting of a number of atoms of grape sugar, from which one or more atoms of water have separated. Quinine, caffeine, and the organic bases or alkaloids in general, contain, besides carbon and the elements of water (oxygen and hydrogen), a certain proportion also of nitrogen. The most complex organic matters, such as the vegetable albumen existing in a dissolved state in vegetable juices, and the vegetable caseine deposited in many seeds, contain not only the four elements of the organic bases, but, in addition to them, a fifth element, namely, sulphur.* The acids so widely distributed in vegetables, such as oxalic acid (in oxalis, rumex, rheum, &c.) ; malic acid (in most unripe fruits) ; citric acid (in the lemon, lime, orange, &c.), and others, stand to each other, and to carbonic acid, in a relation as simple as that between carbonic acid and grape- sugar. By the separation of one oxygen atom from a group of two carbonic acid atoms, oxalic acid (anhydrous) is formed. 2 C0 2 = C. 2 4 ; and C 2 4 C 2 3 = anhydrous oxa- lic acid. If, to a group of two atoms of oxalic acid, two atoms of hydrogen be added, and from the whole two atoms of oxygen be removed, malic acid is the result. 2 C, 3 = C 4 6 ; then C 4 6 + H 2 = C 4 H 2 6 ; and C 4 H, 6 2 = C 4 H 2 4 = malic acid. We have every reason to believe that, by a continuance of such changes, sugar, written C jj |- ; or grape-sugar may be regarded as a multiple of this last formula, C 12 H 12 J , or C 24 H 2 * J , according as we suppose it to be de- rived from twelve or twenty-four atoms of carbonic acid, C 12 04 , or C 84 48 , by the replacement of half the oxygen by tbe same number of atoms of hydrogen, twelve or twenty-four. Caue-sugar (C 12 H^ O xl ), gum and starch (C 12 H 10 10 ), and the substance of the woody cells, or woody fibre (C 12 H g 8 ), may be viewed as groups of twelve atoms of the simplest form TJ *| of grape-sugar, C Q >, (or if grape sugar be a group with twelve atoms of carbon, as atoms of grape-sugar), from which, respectively, one, two, or four atoms of water have separated. W. G. * This is exclusive of the small but essential quantities of alkaline and earthy phosphates (phosphorus, oxygen, and metals) always found in these compounds, and apparently indispensable to their existence. W. G. 204 LETTERS ON" CHEMISTRY. gum, starch, and woody fibre are formed from these acids ; and that they (the acids) are links in a chain exhibiting the gradual conversion of the atom of carbonic acid into sugar and the other more complex organic atoms. Grape-sugar contains, along with carbon, oxygen and hydrogen, exactly in the proportions to form water. The acids above named con- tain, besides the elements of water, a certain proportion of oxygen in excess. By the further addition of hydrogen, therefore, with or without the separation of oxygen, all these acids may pass into sugar. In proportion as the new pro- ducts formed from carbonic acid deviate more and more in composition from that acid, they acquire new properties. The organic acids still possess the acid character of carbonic acid, but in starch or woody fibre this character is entirely lost. The ultimate particles of oxalic acid, tartaric acid, malic acid, citric acid, and sugar, &c., arrange themselves, being crystallisable, in directions determined by an inorganic force ; but in the formation of starch and of cellulose (the substance forming the woody cells) another cause acts, which opposes cohesion, and alters the direction of their attractions. The more complex organic atoms are no longer bounded by straight lines and flat surfaces, but by curved lines and surfaces. The modern researches in organic che- mistry have shed light on the origin and formation of these higher or more complex organic compounds. There has been discovered a whole series of bodies, produced by the union of two more simple organic compounds, yet retaining entirely the chemical character of one of these. This is quite con- trary to the laws of combination in inorganic chemistry, accord- ing to which, as we have always found, the properties of the constituents disappear, to give place to new properties in the compound. Formic acid and oil of bitter almonds (hydride of ben- zoyle) are well-known compounds. They combine to produce the formobenzoilic acid, which in its character as an acid agrees entirely with formic acid, without possessing any .of the properties of the oil of bitter almonds. The formic acid has retained, the oil has lost, its chemical character, in the COUPLED COMPOUNDS. 205 new compound. This, and a host of analogous compounds, although formed of two compound bodies, play the part of one of the more simple constituents : that is, of such as we cannot decompose into still simpler, and again reconstruct at pleasure. In order to distinguish this class of bodies, made up of two compounds, yet retaining the chemical cha- racter of one, from other compounds, they have been called coupled or paired compounds ; and that constituent whose properties disappear, is called the copula. In this sense, formobenzoilic acid is a coupled acid, in which the oil of bitter almonds is the copula. It is supposed that all the higher or more complex organic compounds are thus formed ; and albumen, caseine, and the organic bases are regarded as coupled compounds, which they certainly are, although we do not yet know, and cannot name, the copula belonging to them. By coupling nitrogenised compounds, such as ammonia and hydrocyanic acid, with non-nitrogenised, and also with other nitrogenised bodies, we produce, artificially, compounds possessing all the properties of the nitrogenised acids and colouring matters occurring in nature. Asparagine, a body formed in asparagus and during the germination of the Leguminosce and many other plants, has the composition of malate of ammonia, minus the elements of water. Now, we are able, from malic acid and ammonia, to produce, not as yet asparagine, but aspartic acid, a body derived from asparagine. Orcine, which is colourless and crystallised, produces, when oxygen is present, by absorbing ammonia, the splendid red dye, orceine. The admirable researches of Wurtz and of Hofmann have shown that every one of the three atoms of hydrogen in ammonia may be displaced and replaced by compound organic atoms ; and that in this way new compounds are formed, in which the ammonia retains perfectly its chemical character, as a base. Ammonia neu- tralises acids, forming with them salts ; the new bodies obtained from it by the replacement of its hydrogen are organic bodies, perfectly analogous in chemical characters, not only to ammonia, but also to nicotine, morphine, and quinine. 206 LETTERS ON CHEMISTRY. Universal experience teaches us, that all organised beings after death suffer a change, in consequence of which their bodies gradually vanish from the surface of the earth. The mightiest tree, after it is cut down, disappears, with the exception, perhaps, of the bark, when exposed to the action of the air for thirty or forty years. Leaves, young twigs, the straw which is added to the soil as manure, juicy fruits, &c., disappear much more quickly. In a still shorter time animal matters lose their cohesion ; they are dissipated into the air, leaving only the mineral elements which they had derived from the soil. This grand natural process, of the dissolution of all com- pounds formed in living organisms, begins immediately after death, when the manifold causes no longer act, under the influence of which they were produced. The compounds formed in the bodies of animals and of plants undergo, in the air and with the aid of moisture, a series of changes, the last of which are the conversion of their carbon into carbonic acid, of their hydrogen into water, of their nitrogen into ammonia, of their sulphur into sulphuric acid. Thus their elements resume the forms in which they can again serve as food to a new generation of plants and animals. Those elements which had been derived from the atmosphere take the gaseous form and return to the air ; those which the earth had yielded, return to the soil. Death, followed by the dissolution of the dead generation, is the source of life for a new one. The same atom of carbon, which as a constituent of a muscular fibre in the heart of a man assists to propel the blood through his frame, was, perhaps, a con- stituent of the heart of one of his ancestors ; and any atom of nitrogen in our brain has, perhaps, been a part of the brain of an Egyptian or of a negro. As the intellect of the men of this generation draws the food required for its development and cultivation from the products of the intel- lectual activity of former times, so may the constituents or elements of the bodies of a former generation pass into, and become parts of, our own frames. The proximate cause of the changes which occur in DECAY OF ORGANIC BODIES. 207 organised bodies after death is the action of the oxygen of the air .on many of their constituents. This action only takes place when water, that is, moisture, is present, and requires a certain temperature. At the freezing point of water and at the point of ebullition these changes no longer take place. This influence of atmospheric oxygen is very distinctly seen in fruits and other soft parts of vegetables, when, by an injury to their surface, the juice comes into direct contact with the air. When an apple is bruised at one point, a process of decomposition begins from the injured part. A brown spot appears, which increases in a regular concentric circle, till at last the whole apple becomes rotten, or is changed into a brown, soft, viscid mass. The juice of the grape, while it is protected by the external skin from contact with atmospheric air, scarcely undergoes any perceptible alteration. A grape, by gradual exsiccation, becomes converted into a raisin. The slightest perforation through its external covering, as with the point of a needle, for instance, is sufficient to alter all the proper- ties of the juice. If we cut an apple, a potato, or a beet-root, the cut surface in the course of a few minutes loses its white colour, and assumes a brown tint. Animal fluids comport themselves in a precisely similar manner. Milk, whilst in the udder of the cow, urine whilst in the bladder, undergo, in a healthy state, no alteration of their properties. But in contact with air, milk coagulates without any evolution of gas, and becomes acid ; the caseine separates in the form of a curdy mass ; urine, which is acid, becomes alkaline ; and, after a time, when an acid is added, it effervesces from the escape of carbonic acid gas. In like manner, a process of decomposition sets in, after death, in the bodies of men and animals, which begins in the inside in those parts, such as the lungs, which are in contact with the air. When there are wounds, it spreads from them, and, in diseases, from the diseased part ; so that, in many cases, death itself is nothing else than the result of a decom- 208 LETTERS ON CHEMISTRY. position going on in an inward part. With the disease, of which it is the proximate cause, this process begins, and it continues after death. The most remarkable of these phenomena is certainly this, that, in many cases, the change once begun in organic matters, continues when, after transient contact with the air, the atmospheric oxygen is entirely excluded. Must, the fermenting grape juice, continues to ferment in closed vessels; and the fermenting wine, in the manufacture of champagne, often bursts the strongest bottles. Milk, once exposed to the air, coagulates, and becomes sour even in hermetically sealed vessels. It is obvious that, by the contact of these organic bodies with the oxygen of the air, a process begins, in the course of which their constituents suffer a total change in their properties. This alteration is a result of & change in their composition. Before contact with the oxygen, their con- stituents are arranged together, without action on each other. By the oxygen, the state of rest or equilibrium of the attractions which keep the elements together, has been disturbed in a particle of the substance, and, as a conse- quence of this disturbance, a separation or new arrangement of the elements has been brought about. The continuance of these processes, even when the oxygen, the original exciting cause of them, no longer acts, shows most clearly, that the state of decomposition, which has been produced among the elements of a particle of the mass, exercises an influence on the other particles, which have not been in contact with the oxygen of the air ; for not only the first particle, but, by degrees, all the rest, undergo the same change. All those processes of decomposition which begin in a part of an organic substance from the application of an external cause, and which spread through the whole mass, with or without the co-operation of that cause, have been called processes of Putrefaction. A putrescible substance, therefore, is distinguished from one not putrescible, because the former, without other conditions than a certain temperature, . and PUTREFACTION. 209 the presence of water, (after exposure, although transient, to the atmosphere,) are resolved into a series of new products ; while the latter, if unmixed, do not, under the same circum- stances, undergo any change. The number of substances occurring in nature, which, according to this definition, are truly putrescible, is singularly small ; but they are everywhere diffused, and form part of every organised being. Before all other substances, this property of putrescibility belongs to the highly complex matters of the animal and vegetable kingdoms, which contain nitrogen and sulphur ; such as albumen, fibrine, caseine, gelatine, and the like. Urea, sugar, sugar of milk, asparagine, and amygdaline, as well as the various organic acids, undergo, when pure, under the circumstances above mentioned, (the presence of air and water, with a certain temperature,) no perceptible change. Solution of sugar, and sugar of milk, or of urea, when exposed to a gentle heat, dry up ; the dissolved matters separate in crystals, without losing any of their properties. The examination of vegetable juices, and of animal fluids, such as milk and bile, of grape juice and of urine, &c., shows that they contain two kinds of substances, of entirely different nature and composition ; one which is putres- cible, and along with it, another, or several, which, by themselves are utterly unsusceptible of that spontaneous change. Now, when these fluids, left to themselves, enter into decomposition, we observe the remarkable phenomenon, that both kinds of bodies, the putrescible as well as those which, by themselves, are imputrescible, disappear simul- taneously, being resolved into new products. But the latter bodies, without the presence of the former, would have remained unchanged. If we cause a putrescible body, such as caseine, fibrine, blood, or animal mucus, to enter into putrefaction, and then add to it a solution of sugar, or of sugar of milk, or of urea, &c., these substances pass into fermentation ; that is, into decomposition. It is obvious, from these facts, that putrescible matters, in 210 LETTERS ON CHEMISTRY. the state of putrefaction, when brought into contact with a large number of non-nitrogenised as well as nitrogenised substances, of themselves not putrescible, effect a change of composition in them. It will now be easy to understand the distinction between putrefaction and fermentation. All non-putrescible bodies are called fermentescible, when they possess the property of being decomposed by contact with putrescent matters. The process of their decom- position is now called fermentation. The putrescent body, by which this change is caused, is now named the Ferment. All putrescible substances, in the state of putrescence, become ferments; that is, they acquire in this state the power of causing some one or more of the fermentescible substances to enter into fermentation ; and the putrescent body or ferment retains this power, until its putrefaction is completed. The changes which fermenting bodies undergo, depend on the resolution of a very complex atom into two or more less complex atoms. The 36 elementary atoms in an atom of crystallised sugar, C 12 H 12 12 , are resolved into 4 atoms of carbonic acid, 4 C0 2 , containing 12, and into 2 atoms of alcohol, 2 C 4 H 6 2 , containing 24 simple atoms. The sugar of milk contained in fresh milk (also C 12 H 12 12 ) resolves itself into two atoms of lactic acid, 2 C 6 H 6 6 , containing the same number of elementary atoms as the sugar of milk. Since no foreign element has been added to the sugar of milk, when it was changed to lactic acid, and none of its elementary atoms have been separated or expelled, it is quite certain that the change of properties depends on a change in the position or place of the atoms of the sugar of milk, and that these are arranged in a new order in the lactic acid. By the cause which effected, the change, it is obvious that the atoms of the sugar of milk must have been set in motion ; for in order to arrange themselves in a new order, they must move. Putrescent bodies exert an action on complex organic atoms, which, by themselves, are not putrescible ; it is certain that PUTREFACTION AND FERMENTATION. 211 their action depends on a certain state in which their atoms are ; it is further certain, that this state is one of change of place, or a resolution into simpler atoms of the complex atoms of the putrescent body ; and it is equally undeniable, that by their contact with fermentescible bodies, the elements of the latter also assume new positions ; whence it follows, that the atoms of fermentescible bodies, in contact with putrescent matters, behave as if they formed part of the putrescent substance. The atoms of the fermentescible body (sugar, &c.) participate in the motion of the atoms of the ferment ; the change of position or state of motion in the ferment causes the atoms of carbon, hydrogen, and oxygen of the fermentescible body also to change their position or place. Hence we can see why these processes have a beginning, a certain duration, and an end, in which respects they are distinguished from ordinary cases of chemical action. When we add sulphuric acid to a salt of baryta, decomposition instantly takes place at all points where the acid comes in contact with the baryta. The beginning is at the same time the end, and the elements of the sulphate of baryta, when formed, have no further action. But a putrefying body goes through a whole series of changes, and in every stage it exerts a peculiar action. When a change has been effected in the position or arrange- ment of the atoms of sugar in grape juice, or in infusion of malt, no further change takes place with regard to these atoms ; but the change in the altered substance (a compound containing nitrogen and sulphur), which has acted as a ferment and has separated as yeast, continues to go on. If the yeast be taken out of the fermented liquor, and added to a solution of sugar, a number of sugar atoms undergo the former change, as in the grape juice or malt infusion ; and the yeast or ferment retains this power, until it has gone through the entire series of changes belonging to its putre- faction, until the separation and new arrangement of its atoms are complete, and a state of rest or equilibrium is attained. If, after this point, sugar be still present, its p 2 212 LETTERS ON CHEMISTRY. atoms remain unchanged. According to the amount of ferment present, the time required for the fermentation is determined. By doubling or tripling the proportion of ferment, the time is shortened, or a larger quantity of the sugar or other fermentescible body is decomposed. If we divide a vessel containing a solution of sugar into two cells by a partition of filtering paper, which allows the dissolved sugar to pass through, but not the globules of the yeast, and if we add yeast to the solution in one cell, fermen- tation occurs in that cell only ; that is, where sugar atoms and yeast atoms come into contact, there alone the resolu- tion of sugar into alcohol and carbonic acid takes place. The action of ferments on fermentescible bodies is analo- gous to that of heat on organic substances. Their decom- position at high temperatures is always the result of a change in the position of their atoms. Heat causes an expansion, or increase of volume ; at first it affects the adhesion of the atoms as grouped ; and at a higher temperature the atoms constituting the groups separate from each other. Heat disturbs the equilibrium of attractions among the atoms ; the liquid and gaseous states are new states of equilibrium between the effects of heat and those of cohesion, as ap- plied to the groups of atoms. When, at a high temperature, the complex atoms or groups constituting organic matters are decomposed, they always yield products which are per- manent and unchangeable at that temperature, but which are destructible by a higher one. Every fixed degree of heat corresponds to a peculiar state of equilibrium between heat and the chemical attraction which keeps together the ele- ments of organic atoms. We cannot render a piece of sugar liquid, let us grind it ever so finely ; and still less can we decompose an atom of sugar by mechanical force, or detach from it an atom of car- bon or hydrogen. We can, by shaking a solution of sugar, cause the particles of sugar and those of water to move on one another ; but their elements do not, in this case, change their relative position. In putrefaction and fermentation, it is not the groups of HEAT MODIFIES FERMENTATION. 213 atoms, but the atoms in the groups, which change their place ; and it is this internal motion, in putrescent bodies, which causes change of place in the atoms of the ferment- escible body ; that is, when the chemical force which holds their elements together, is less than the force which tends to separate them. The influence of temperature on the nature of the pro- ducts of fermentation is truly remarkable. The juice of carrots, beet-root, or onions, which is rich in sugar, when allowed to ferment at ordinary temperature, yields the same products as grape juice. But, at a higher temperature, the whole decomposition is changed. There is observed a much less copious evolution of gas, and no alcohol is formed. If we examine the fermented liquid at the end of the fermenta- tion, there is no longer in it any sugar. But a large quan- tity of lactic acid, and a body resembling gum arabic ; and, as the most remarkable product, a crystallisable substance, in composition and properties identical with the chief con- stituent of manna, namely mannite ; all these are found to have been produced. Alcohol and carbonic acid are the products of the decom- position of sugar by fermentation at the ordinary tempera- ture ; carbonic acid, mannite, lactic acid, and gum, are the products of its fermentation at a higher temperature. The kind of fermentation of milk-sugar in milk, when it passes into lactic acid, chiefly occurs at ordinary temperatures. At a heat of from 76 to 96 F., the caseine acquires the properties of common yeast, and there occur, in the milk sugar, at these higher temperatures, two successive trans- formations. It first passes into grape sugar, by taking up the elements of water, and then, by contact with the caseine or cheese (the ferment), it is resolved into alcohol and carbonic acid. At the ordinary temperature, milk ferments without evolution of gas, and lactic acid is formed. At higher tem- peratures we obtain, as the result of the altered fermentative process, an alcoholic liquid, which by distillation yields true spirits. 214 LETTERS ON CHEMISTRY. It is obvious that only those bodies are fermentescible in which the elements are mobile, and only held together by a feeble attraction ; and if, in fact, by the change of place, or motion, in the elements of the ferment, a similar change, or motion, has been induced in the particles of another body in contact with them, it is certain that the atoms of the latter opposed to the motion acting on them a resistance, which had to be overcome, before they could be set in motion. This resistance, how feeble soever we may suppose it, acts like a force, which must re-act on the atoms of the ferment, whereby the change or motion among them must be altered in its character. A putrescent body, therefore, in contact with a fermentescible one, which it causes to enter into fermentation, must yield products different from those obtained when it putrefies alone. We observe, in fact, that, when solution of sugar is added to putrescent animal cheese, or blood, the beginning of the fermentation is attended by the diminution of the formation of those products which give their offensive smell to putrid animal matters ; so that, in the course of the process, these striking products entirely disappear. It is further plain, that a fermentescible body must cease to be fermentescible when the resistance opposed to the action of the ferment on its atoms is increased, or the force which holds the atoms of the ferment in groups, is strengthened. There are indeed many bodies which oppose putrefaction and fermentation, and which impede or arrest the course of these processes ; and this remarkable action, frequently depends on their forming a chemical compound with the ferment. By the addition of a body having affinity to the ferment, the tendency of its particles to retain their original arrangement is obviously strengthened ; for, in addition to the force which holds them in groups, we have in the new body, which combines with the ferment, a new attraction, which must be overcome before the atoms of groups of the ferment can change their position. To the list of bodies which check putrefaction and -fer- mentation, or antiseptics, belong all substances which exert a chemical action on ferments ; such as alkalies, mineral FERMENTS. 215 acids, concentrated vegetable acids, volatile oils, alcohol, sea salt. The most effective are sulphurous acid, metallic salts, especially those of mercury, which combine chemically with the ferments or putrescent bodies. Arsenious acid does not prevent the putrefaction of the blood, nor the ordinary alcoholic fermentation of sugar but the putrefaction of the skin and of the gelatinous tissues is entirely suppressed by the presence of arsenious acid. Many organic acids, in the form of their lime salts, are fermentescible, although not so by themselves. Malate of lime ferments with yeast, as readily as solution of sugar. At a low temperature pure carbonic acid gas is evolved, and the malate is resolved into succinate, acetate, and carbonate of lime. At a higher temperature, hydrogen gas is evolved, and there is produced, from the malic acid, a large quantity of butyrate of lime. Lactate of lime yields, in contact with putrid cheese, carbonic acid and hydrogen gases, butyric acid, and mannite. Tartrate of lime yields carbonic acid, metacetonate, and acetate of lime. By the neutralisation of these acids with lime, their chemical action on the ferment is prevented as they are formed ; and the liquid remains neutral during the process, because the lime set free by the formation of organic acids of a higher order, and of a less capacity of saturation, is deposited in the form of insoluble carbonate. The ferments present in grape juice and other vegetable juices are, without exception, such bodies as have the same composition as blood or cheese. The production of these blood-constituents in plants, in the vine for example, may be increased and exalted by animal manure. Cow-dung and urine being rich in carbonated alkalies, exerts its influence chiefly on the amount of sugar, that is, of the fermentescible body. Human excrements, on the other hand, contain only phosphates, and act most powerfully on the production of the blood-constituents (or albuminous matters), that is, of the ferments, in plants. It is easy to see, that by careful cultivation, by a proper 216 LETTERS ON CHEMISTRY. choice of manures, we can affect most decidedly the quality of the juice (for example, of the grape). When the grape juice, or must, is rich in albuminous ferments, we act rationally in adding sugar to it, although that sugar may have been formed in another plant, or when we add to the juice of the unripe grapes of our climate the ripe dried raisins of a more southern one. Scientifically speaking, these additions are true improvements, which in no sense can be regarded as deceptive adulterations. Changes in the nature of the products occur in every kind of fermentation, caused partly by changes of temperature, partly by the presence of other bodies than the chief fermentescible one, which are drawn, as it were, into the process of transformation. Thus we obtain from the same grape juices, when fermented in different temperatures, wines of different quality and character ; for, according as the temperature of the air in the harvest season is high or low, according to the depth of the fermenting cellar and its temperature during the fermentation, the quality, the smell, and the taste of the wine varies. A constant temperature in the fermenting cellar, and a fermentation, not tumultuous, but gradual and steady, are the most favourable conditions within our power to be realised, for producing a noble or first growth wine. It will not be long before the wine-growers employ in the manufacture of wine the deep rocky cellars which are found so advantageous for the making of the finer sorts of beer, in preference to all others; and the advantage of these cellars depends chiefly on their constant temperature. The influence which extraneous substances exercise upon the products of vinous fermentation is strikingly exemplified in the fermentation of potato-mash. It is well known that in the manufacture of potato-spirit an oily-liquid is obtained, besides the alcohol, possessing poisoning properties, a highly disagreeable smell, and nauseous taste ; this is called oil of potato-spirit, or fusel oil. It does not exist ready formed .in the potato, but is a product of the transformation of sugar; for it is produced not only in the fermented potato-mash, BOUQUET OF WINES. 217 but also in the fermentation of the last syrups obtained during the preparation of the beet-root sugar. This fusel oil belongs, by its chemical properties, to the same class of bodies as alcohol ; it is an alcohol from which the elements of water have been separated. Two atoms of fusel oil are formed by the aggregation of five atoms of alcohol, with the separation of six atoms of water. Fusel oil is produced in our spirit manufactories, as an accidental and accessory product, in such large quantities that it is used for lighting the buildings. Its formation never takes place in fermenting fluids containing racemic acid, tartaric acid, tartar, or bitartrate of potash, or citric acid, or certain bitter substances, such as hops, or the extract or volatile oil of hops. Fusel oil is formed principally in alkaline or neutral fluids, and in such as contain lactic acid or acetic acid, and its pro- duction in the potato-mash may be prevented, in a great measure, by the addition of tartar to the fermenting fluid. The odour and flavour of wines depend invariably upon certain combinations which are formed during fermentation. Old Rhine wines contain acetic ether, many of them a very minute proportion of butyric ether, which impart to them a peculiar and agreeable smell and taste, somewhat resembling old Jamaica rum. All wines contain cenanthic ether, iipon the presence of which depends their vinous odour. These various compounds are formed partly in the process of fermentation and partly while the wine is in the cask, by the action of acids, which are present, upon the alcohol of the wine. (Enanthic acid seems to be produced by fermen- tation ; at least it has not been detected in the grape. The free acids which are present in the fermenting juice take a most decided part in the formation of those aromatic matters upon which odour and flavour depend. The wines of southern regions are produced from perfectly ripe grapes ; they contain tartar, but no free organic acids ; they scarcely possess the characteristic odour of wine, and with respect to bouquet or flavour they cannot bear a comparison with the nobler French or Rhenish wines. 218 LETTERS ON CHEMISTRY. LETTER XVIII. Vegetable Caseine and the Emulsion of Almonds as Ferments Effects of the latter body on Salicine and Amygdaline Oil of Mustard Gluten of Flour as a Ferment Transformation of Starch into (him and Sugar Germination and Malting Maturation of Fruits Skin and membranes agree in many properties with Gluten and Yeast Making of Cheese Action of the Lining Membrane of the Stomach in Digestion Pepsine does not exist Theory of the Action of Ferments Various kinds of Ferments. THE properties of common animal caseine (cheese), and the influence which its particles, when in a state of decomposition and transposition, exercise upon the particles of sugar in contact with them, are very remarkable and interesting ; but far more extraordinary, and of surpassing interest, are the properties and action of vegetable caseine, as it is contained in the milk of almonds. It is universally known that when sweet" almonds are reduced to a pulpy mass, mixed and rubbed down with from four to six times their weight of water, they yield a fluid, exhibiting, in its external appearance and pro- perties, the greatest analogy to very rich cow's milk. The milky appearance of almond emulsion is caused by particles of oil, or fat in a state of minute mechanical division, being diffused through it, and these rise to the surface when this fluid is left at rest, and arrange themselves in the form of cream, just as is the case with the milk of the cow. Almond- milk, like animal milk, coagulates upon the addition of vinegar, and after a certain time, if left to itself, it turns sour. This milk contains a substance exactly analogous, in its properties, to animal caseine or cheese, and of the same ready mutability. The cheese of animal milk begins to undergo alteration from the instant it leaves the udder .of the cow, and the change proceeds in it continuously, although it only becomes perceptible after the lapse of some time in VEGETABLE CASEINE.-SALICINE, 219 the coagulation of the milk. In a manner precisely similar, transformation takes place in the elements of vegetable caseine, from the very moment that sweet almonds are converted into almond-milk. The vegetable caseine of the almond, like animal caseine, contains sulphur, but it contains a larger proportion of nitrogen than the latter substance. The cir- cumstance that animal caseine does not produce the same effect as a ferment in all cases is, perhaps, to be ascribed to its inferior amount of nitrogen. With respect to their influence upon the fermentation of sugar, the properties of animal and vegetable caseine are identical. If to a solution of grape-sugar (which is the same in composition as starch-sugar and the solid part of honey) milk of almonds, or pounded almonds freed by means of cold pressure from their mixed or fatty oil, be added, and the mixture be kept in a warm place, it will soon run into a lively vinous fermentation, and a brandy of a peculiar, but highly agreeable, flavour, may be obtained by distillation from the fermented fluid. Animal caseine also produces the same effect ; but the vegetable caseine of almond-milk causes decompositions and transformations in a number of organic compounds, such, for instance, as salicine and amygdaline, which animal caseine does not produce. Salicine is that constituent of the bark of the willow which imparts to it its well-known intensely bitter taste, and the property of assuming a carmine red tint when moistened with a few drops of concentrated sulphuric acid. Salicine may be very easily extracted from willow-bark by means of water. In its pure state it presents the form of white, shining, long, needle-like crystals, interwoven with each other like a silken web. Salicine, like sugar, is devoid of nitrogen. If salicine is placed in almond milk, its bitter taste soon disappears, and is replaced by a purely sweet flavour. At this juncture all the salicine has vanished, and we have grape-sugar in its place, together with a new substance totally different from salicine, namely, saliyenine. 220 LETTERS ON CHEMISTRY. Sugar and saligenine, together, contain the elements of salicine. An atom of salicine, upon coming into contact with the caseine of almond-milk, is resolved into one sugar atom and one saligenine atom, without the addition or with- drawal of any element whatever. The deportment of this vegetable caseine toward amygda- line is even still more remarkable. The peculiar products which are obtained from bitter almonds were, for a long time, considered to be a problem, nearly, if not altogether, inex- plicable, until amygdaline was discovered to be a constituent of bitter almonds, and the changes it undergoes from the influence of vegetable caseine were brought to light. If bitter almonds are finely powdered, mixed with water, and submitted to distillation, an aqueous fluid is obtained, with a strong odour, exhibiting a milky appearance from a number of small oil-globules being suspended in the fluid ; these globules of oil coalesce, subside, and form a stratum of oil at the bottom of the vessel. This oil is, therefore, heavier than water ; it is also volatile, and has a powerful smell and taste of bitter almonds : moreover, it is characterised by the property of solidifying, when exposed to the air, with the absorption of oxygen, into inodorous crystals of benzoic acid. Besides this volatile oil, which is an article of commerce to a considerable amount, being used in perfumery, the water passing over contains also a considerable proportion of hydro- cyanic acid. Neither of these two products of the distillation of bitter almonds with water, namely, hydrocyanic acid and oil of bitter almonds, can be detected by any means in the bitter almond itself. Were they contained in the bitter almond, as oil of turpentine exists in the resin of the pine, or oil of roses in the rose-petals, we might, of course, feel assured that they would admit of being extracted from the almonds by means of fatty or fixed oils, or other solvents. But the fat oil, which is easily obtained from bitter almonds by pressure, is as bland and insipid as that expressed from sweet almonds ; not the slightest trace of hydrocyanic acid, nor of the volatile oil of bitter almonds, can be detected in it, although both substances are readily soluble in it. If FERMENTATION OF AMYGDALINE. 221 bitter almonds are boiled with alcohol, not a trace, either of hydrocyanic acid, or of the volatile oil of bitter almonds, is found in the alcohol ; but, upon evaporation, a white crys- talline substance is obtained, of easy solubility in water, which imparts to its solution a slightly bitter taste. This substance differs materially from sugar and salicine by invariably con- taining a small amount of nitrogen. It is termed AMYGDALINE. The discoverer of this substance concluded that the hydro- cyanic acid and volatile oil of bitter almonds are formed from it, or that the elements, the combination of which furnish those two bodies, must have aggregated, through the action of alcohol, to form amygdaline. Not finding any key to this enigma, he (as is but too frequently done) ascribed the forma- tion of amygdaline, or the transformation of its elements into hydrocyanic acid and oil of bitter almonds, to the co-opera- tion of an intangible and invisible something, which, from its nature, must be beyond the reach of our understanding. All these phenomena admit of a very simple explanation. We now know that upon bringing a solution of amygdaline and water into fresh almond-milk, decomposition takes place in the course of a few seconds, and the amygdaline atom, in consequence of a new mode of molecular arrangement, resolves itself into hydrocyanic acid, volatile oil of bitter almonds, and sugar, the atoms of which, ninety in number, were, with the exception of four atoms of water, which have been taken up, aggregated into one group in the amygda- line atom ; that is, the amygdaline is constituted of the elements of all these substances combined into a single group or atom. The quantity of amygdaline which, under these circum- stances, is, through the agency of vegetable caseine, separated into those different compounds, depends, in a certain measure, upon the amount of water present in the mixture. Whether the water is sufficient to dissolve all the new-formed products, or insufficient for that purpose, determines whether all the amygdaline or only a part of it becomes decomposed. The volatile oil of bitter almonds requires thirty parts of water for its solution, the other products require less. If, therefore, 222 LETTERS .ON CHEMISTRY. only so much amygdaline is added to the almond-milk as to produce one part of oil of bitter almonds for every thirty parts of water present, the whole of the amygdaline disappears ; if more amygdaline than this proportion is added to the mixture, the amygdaline added in excess undergoes no alteration. It is very evident that the chemical affinity of the water, that is, its solvent power, plays a part in this process of transformation ; its affinity or attraction for one of the products co-operates as a cause of decomposition. Now, since the white constituent of bitter almonds is absolutely identical with the vegetable caseine of sweet almonds, it may easily be conceived that the amount of amygdaline existing, as such, in almonds, depends solely upon the greater or lesser amount of moisture contained in them. A quantity of amygdaline, corresponding to the small amount of moisture in the almonds, is only to be traced in the form of the products of its transformation. When the almonds are finely powdered and mixed up with a large amount of water when they are converted, for instance, into almond milk, the amount of amygdaline decreases with the increas- ing proportion of water added, until, at last, upon the further addition of water, it altogether disappears. The deportment of amygdaline, with the white caseous constituent of almonds, assumes a still higher degree of in- terest when we consider that the presence of amygdaline in the almonds depends upon the accidental position of the tree upon which they grow. Botanists can find no perceptible difference between two trees, one of which bears sweet, the other bitter almonds. Instances are known of trees bearing bitter almonds which, by simple transplantation, were made to produce sweet almonds j and this is certainly one of the most interesting examples of the influence which certain con- stituents of the soil exercise upon the vital processes of plants. The effect of the presence of water upon the existence of certain organic combinations is abundantly evident from the foregoing facts ; there are, however, other instances which may be adduced in illustration, so highly interesting in them- OIL OF MUSTARD. GLUTEN. 223 selves, that we cannot avoid introducing them in connection with this subject. It is well known to every one that mustard-seed powdered, and formed into a paste with water, yields in the course of a few minutes a mixture which, placed upon the skin, produces excessive irritation, so much so as even to raise blisters. This action is caused by a volatile oil containing sulphur, but free from oxygen. This oil may be obtained from mustard by distillation with water, in the same manner as the oil of bitter almonds is obtained from bitter almonds. It is to this volatile oil that the mustard eaten at table owes its smell and taste. In its purest state it is frightfully acrid and pun- gent. Now, in the mustard-seed there exists no trace of this oil ; the fixed oil expressed from mustard-seeds is bland and destitute of any pungency. The volatile oil is formed from a substance rich in sulphur and nitrogen, and possessing itself no pungency. This substance, by the action of the vegetable caseine contained in the mustard-seeds, undergoes decomposition immediately upon the addition of a sufficient amount of water, and the volatile pungent oil is one of the new products originating from the transposition of the elements. As vegetable caseine, in the seeds of mustard and in almonds, exercises a decomposing influence upon the other constituents of the same seeds, in consequence of the state of transformation into which it passes immediately upon com- ing into contact with water, so also the similarly constituted sulphur and nitrogen compounds of nearly all seeds comport themselves, and especially that contained in the grain of the cereals, well known under the term gluten. The flour of wheat, rye, or any of the cereals, when mixed with twenty times its amount of water at 75 C., =167 F., yields a thick paste, which, after the lapse of a few hours, becomes thin and fluid, and assumes a very sweet taste. The starch of the flour absorbs a certain amount of water, and, in consequence of a new manner of arrangement of its atoms, changes first into a kind of gum, and then into grape-sugar. This transformation is caused by the gluten of 224 LETTERS ON CHEMISTRY. the flour passing itself into a state of decomposition. The liquefaction of the dough in the preparation of bread depends upon the same cause. The same formation of sugar takes place in the germina- tion of corn. All the starch contained in wheat, barley, rye, &c., becomes, during the development of the germ, converted into sugar by the action of the adjacent particles of gluten. The gluten itself assumes quite altered properties j it be- comes soluble in water, like starch. If the aqueous extract of germinated corn (malt), prepared in the brewing of beer, which is called sweet- worts, is heated to the boiling point, a quantity of the gluten which had be- come soluble and dissolved in it, separates in a state in which it cannot be distinguished from coagulated animal albumen. The remaining portion of the gluten is contained in the worts; and when it is boiled with hops, concentrated by evaporation, and mixed with beer yeast, there is obtained, after fermentation, beer ; while the dissolved gluten separates as beer yeast, in a quantity 20 to 30 times greater than that of the yeast added to the worts. In living organisms we observe, on the great scale, pheno- mena of a similar kind, dependent upon identically the same, or, at least, closely analogous causes. Many plants with woody stems are found to contain in autumn a matter perfectly like the starch of potatoes, or of the cereals, depo- sited in the substance of the wood, which in the spring, when the plants re-awaken to life, becomes converted into sugar. The ascending juice of the maple is so rich in sugar that in regions where this tree occurs in such numbers as to form forests, its juice is employed in the manufacture of sugar. We have every reason to believe that this sugar is formed by a transformation of starch, in a precisely similar manner as the sugar of germinating seeds. The maturation, as it is called, or sweetening of winter fruits, when stored up for their preservation in straw, is the result of a true fermentation. Unripe apples and pears con- tain a considerable amount of starch, which becomes con- verted into sugar by the nitrogenous constituent of the juice RENNET. 225 . passing into a state of decomposition, and transmit- ting its own mutations to the particles of starch in contact with it. Kedtenbacher has recently found formic acid to be a pro- duct of the fermentation of the leaves and twigs of pines. This discovery is the more interesting, as it will probably enable us to explain the presence of this acid in ants, espe- cially in those species of these animals which, for their nourishment, partake of substances which can produce no formic acid. The skin of animals, the mucous membrane of the stomach and intestines, and the uninary bladder, have many proper- ties in common with gluten and yeast. In their fresh state these substances exercise not the slightest influence upon starch or milk-sugar, but when placed in water for a few hours, or even when simply exposed to the atmosphere, they quickly pass into a state of decomposition, which renders them capable of converting with great rapidity starch into sugar, and milk-sugar into lactic acid. This property of the mucous membrane of the stomach of the calf has been made use of from time immemorial, in the preparation of cheese, in order to make milk coagulate, or, in other words, to effect a separation of the cheese from the other constituents of milk. The solubility of cheese in milk is in consequence of the presence of alkaline phosphates and of free alkalies. In fresh milk these substances may be easily detected by the property it possesses of restoring the blue colour to reddened litmus-paper. The addition of any acid, by neutralising the alkali, causes the cheese to separate in its naturally insoluble state. The acid indispensable for the coagulation of milk is not added to the milk in the preparation of cheese, but it is formed in the milk at the expense of the milk-sugar present. A small quantity of water is left in contact with a small piece of a calf's stomach for a few hours or for a night ; the water takes up a quantity of the decomposed mucous membrane so minute as to be scarcely ponderable ; this, called rennet, is mixed with milk ; its state of transformation 226 LETTERS ON CHEMISTRY. is communicated (and this is here the most important circum- stance) not to the cheese, but to the milk-sugar, the elements of which transpose themselves into lactic acid, which neutral- ises the alkali, and thus causes the separation of the cheese. By means of litmus-paper the process may be followed and observed through all its stages ; the alkaline reaction of the milk ceases as soon as the coagulation begins. If the cheese be not immediately separated from the whey, the formation of lactic acid continues, the fluid turns acid, and the cheese itself passes into a state of decomposition. Fresh cheese-curd, carefully freed from water and milk- sugar, by expression, and the addition of salt, is a mixture of caseine and butter ; it contains all the phosphate of lime, and part of the phosphate of soda, of the milk. When kept in a cool place, a series of transformations takes place, in consequence of which it assumes entirely new properties ; it gradually becomes semi-transparent, and more or less soft throughout the whole mass ; it exhibits a feebly acid re- action, and develops the characteristic caseous odour. Fresh cheese is very sparingly soluble in water, but after having been left to itself for two or three years it becomes especially if all the fat be previously removed almost completely soluble in cold water, forming with it a solution, which, like milk, is coagulated by the addition of acetic acid or the mineral acids. The cheese which, while fresh, is insoluble, returns during the maturation, or ripening, as it is called, to a state similar to that in which it originally existed in the milk. In those English, Dutch, and Swiss cheeses, which are nearly inodorous, and in the superior kinds of French cheese, the caseine of the milk is present in its unaltered state. The odour and flavour of cheese is owing to the decomposition of the butter ; the non-volatile acids, margaric acid and oleic acid, and the volatile butyric acid, capric and caproic acids, are liberated in consequence of the decomposition of glycerine (the sweet principle of oils, or, as it might be termed, the sugar of oil). The voktile acids impart to cheese its characteristic caseous odour, and the differences in its pungency or aromatic flavour depend CHEESE. 227 .upon the proportion of free butyric, capric, and caproic acids present. The transition of caseine from its insoluble into its soluble state depends upon the decomposition of the phosphate of lime by the margaric acid of the butter ; margarate of lime is formed whilst the phosphoric acid combines with the caseine, forming a compound soluble in water. The bad smell of inferior kinds of cheese, especially those called meagre or poor cheeses, is caused by certain fetid products containing sulphur, and which are formed by the decomposition or putrefaction of the caseine. The alteration which the butter undergoes (that is, in becoming rancid), or which occurs in the milk-sugar still present, being trans- mitted to the caseine, changes the composition of the latter substance and deteriorates its nutritive properties. The principal conditions for the preparation of the superior kinds of cheese (other obvious circumstances being, of course, duly regarded), are a careful removal of the whey, which holds the milk-sugar in solution, and a low tempera- ture during the maturation (or ripening) of the cheese.* The differences in flavour and odour of various kinds of cheese depend upon the methods employed in their manufac- ture upon the state of the rennet when added to the milk upon the addition of salt, and upon the state of the atmosphere during the period of making. It must be admitted that the plants, and especially the aromatic plants, upon which the animals feed, exercise some influence upon the quality of the cheese ; but this influence is veiy slight * The quality of Roquefort cheese, which is prepared from sheep's milk, and is very excellent, depends exclusively upon the places where the cheeses are kept after pressing, and during maturation. These are cellar*, communicating with mountain grottoes and caverns, which are kept Con- stantly cool, at about 41 to 42 Fahr., by currents of air from the clefts in the mountains. The value of these cellars, or storehouses, varies with their property of maintaining an equable and low temperature. Griron (Ann. de Chimie et de Physique, xlv. 371) mentions, that a certain cellar, the construction of which had cost 480 (12,000 francs), was sold for 9200 (230,000 francs), being found to maintain a suitable temperature. A convincing proof of the importance attached to temperature in the pre- paration of these superior cheeses. Q 2 228 LETTERS ON CHEMISTRY. and subordinate. The milk of the cow in spring, summer, and autumn, is very unequal in its composition, but this does not occasion any perceptible difference in the cheese prepared in one and the same dairy. If the plants upon which the cows feed exercised any considerable influence upon the quality of cheese, the same pastures could not, at different seasons, furnish cheese of similar quality, inasmuch as the development and flowering of the different species of plants from which the milk is derived, belong to various seasons. I have, by personal inspection, satisfied myself that the method of preparing the cheese is quite different in Cheshire from that practised in Gloucestershire, and this, again, differs from the plan pursued in the manufacture of Stilton cheese. The lining membrane of the stomach of the calf, and the mucous membrane of the stomach of animals generally, besides the power of converting milk-sugar into lactic acid, possess the property of rendering soluble, or liquefying, solid animal matters, when weak hydrochloric acid is present. The phenomena observed in this chemical operation have thrown a new and unexpected light upon the process of DIGESTION in the living animal organism. All ferments, as they are called, that is, substances which are capable of exciting fermentation, possess also, in a certain stage of their transformation, this power of liquefying and rendering soluble various aliments. We have already seen that extract of malt, and gluten, possess this power in reference to starch, but these are far surpassed in this property by the mucous membrane of the stomach. If a small portion of calf's stomach or rennet is placed for a few hours in warm water, mi^pd with so small an amount of hydrochloric acid as scarcely to impart an acid taste to the water, a solution is obtained which acts upon boiled meats, upon gluten, and upon hard-boiled white of egg, in exactly the same manner, as the gastric juice in the living stomach. This artificial digestive fluid is like gastric juice, inasmuch as both have an acid reaction, owing to the presence of hydrochloric acid. DIGESTION. PEPSIKE. DIASTASE. 229 When pieces of muscular fibre, or hard-boiled albumen, are exposed in this artificial digestive fluid to a temperature of 37 C. (the temperature of the stomach = 98'3 Fahr.), they speedily become slimy, and transparent at the edges, and after the lapse of a few hours they become dissolved into a fluid rendered slightly turbid by particles of fat. The dissolving power of the hydrochloric acid, per se, becomes, by the addition of a scarcely ponderable amount of mucous membrane, in a state of decomposition, accelerated so greatly, that solution takes place in a fifth part of the time which is required under ordinary circumstances. Physiologists have observed that in digestion the whole of the inner surface of the membrane of the stomach, the epithelium, separates completely from the other layers of the membrane. It cannot be disputed that this epithelium, in coming into contact with the oxygen which the saliva carries into the stomach, inclosed in its air bubbles or froth, undergoes an alteration, in consequence of which the contents of the stomach are dissolved in the shortest possible time. It was for a long time believed that the accelerated dissolving power, which the mucous membrane of the stomach imparts to the hydrochloric fluid, depended upon the presence of a particular substance called pepsine, a kind of digestive agent. The same opinion prevailed respecting a substance called diastase, contained in the extract of malt, by which starch is converted into sugar ; and these sub- stances have received certain designations. But what have been called pepsine and diastase are nothing more than a portion of mucous membrane, or of gluten, having passed into a state of decomposition. The action of these bodies depends entirely upon their condition, just as is the case with yeast. With a piece of the mucous membrane of the stomach, in a certain stage of decomposition, we may render certain animal substances soluble ; whilst, with the same membrane, in other stages of decomposition, we may convert starch into sugar, sugar into lactic acid, mannite, and mucilage ; or into 230 LETTERS ON CHEMISTRY. alcohol and carbonic acid : and lactic acid into butyric acid, hydrogen, and carbonic acid. In the same manner a watery infusion of fresh malt will convert starch-paste, in the space of a few minutes, into grape-sugar. The infusion or extract of malt loses this property after the lapse of a few days, and, in its stead, acquires the power of converting grape-sugar into lactic acid, mannite, and gum. And again, after eight or ten days, this power is also lost, the infusion becomes turbid, and it now causes the resolution of the sugar atom into alcohol and carbonic acid. The phenomena we have described, if considered in their true signification, prove that the decompositions and trans- formations which occur in the processes of fermentation, are effected by matter, the smallest particles or atoms of which are in a state of motion and transposition, a state susceptible of being communicated to other atoms in contact with the former, so as to cause the atoms and elements of these latter also, in consequence of the resulting disturbance of the equilibrium of their chemical attraction, to change their position, and to arrange themselves into one or more new groups. We have observed that the products formed during fer- mentation alter with the temperature, and with the state of transformation in which the particles of the ferment exist. Hence it is obvious that the new manner of molecular arrangement, which determines the nature and properties of the new-formed products, stands in a definite and imme- diate relation to the mode and manner, direction and energy, of the motion and force acting upon them. All organic substances become exciters of fermentation as soon as they pass into a state of decomposition ; the changing condition once imparted, propagates itself in every organic atom, which is not itself, that is, by its own inherent energy, capable of annihilating the imparted motion, by presenting an adequate resistance. Putrescent flesh, blood, bile, urine, the mucous membrane of the stomach, have this property in common with sub- ATOMIC MOTION COMMUNICABLE. 231 stances occurring in certain parts of plants, or in the vegetable juices. All substances capable of exciting fer- mentation, that is, as we understand it, all those complex atoms which, upon the mere contact of water or of oxygen, pass into a state of decomposition, possess certain properties in common ; but every one of these, also, produces certain effects peculiar to itself, and it is in this respect they differ essentially from each other. These latter peculiar and individual actions and effects stand in the closest relation to their composition. Thus, the vegetable caseine of almonds acts upon*starch and sugar precisely like gluten or yeast ; but gluten and yeast are not capable of resolving salicine into saligenine and sugar, or amygdaline into hydrocyanic acid and oil of bitter almonds. In like manner, animal membranes, in a certain condition, acquire all the properties of fermenting animal cheese or caseine, but the latter substance has no perceptible influence upon the solvent power of hydrochloric acid, upon the lique- faction of coagulated albumen and flesh. All the phenomena of fermentation when taken together establish the correctness of the principle long since recognised by Laplace and Berthollet, namely, that an atom or molecule put in motion by any power whatever may communicate its own motion to another atom in contact with it. This is a dynamical law of the most general application, manifested everywhere, when the resistance or force opposing the motion, such as the vital principle, the force of affinity, electricity, cohesion, &c., is not sufficiently powerful to arrest the motion imparted. This law has only recently been recognised as a cause of the alterations in forms and properties which occur in our chemical combinations ; and its establishment is the greatest and most enduring acquisition which chemical science has derived from the study of fermentation. 232 . LETTERS ON CHEMISTRY. LETTER XIX. Oxygen is the exciting cause of Putrefactive Transformations, all of which begin with Decay or slow Combustion Eremacausis, or decay, is a pro- cess of combustion at the common temperature Examples of Erema- causis in'Bleaching ; Decay of animal matter Decay or Ertmacausis of Alcohol; Acetification, Nitrification, the Eremacausis of Ammonia Making of Wines : of Beer Bavarian Beer : cause of its superiority Application of the same to hasten the Ripening of Wines. THE immediate and most energetic cause of all the altera- tions and transformations which organic atoms undergo is, as I have stated in the preceding letter, the chemical action of oxygen. Fermentation and putrefaction manifest them- selves only in consequence of the commencement of a process of decay; their completion is the restoration of a state of equilibrium. Whilst the oxygen is in the act of combining with any one of the elements of an organic substance, the original state of equilibrium of attraction in all its elements is destroyed, the substance decomposes, resolving itself, in consequence of all the. molecular attractions being again equalised, into a series of new products, which undergo no further change in their properties unless further causes of disturbance or alteration are brought to operate upon them. But although the chemical action which the elements of organic atoms exercise upon each other in fermentation and putrefaction balances itself, in such a manner that a state of rest is induced between the attractions of the new formed products, yet this equilibrium does not exist with respect to their attraction for oxygen. The chemical action of oxygen upon organic substances ceases only when the capacity of the elements to combine with oxygen is exhausted. That action consists in nothing more than the affinity, or tendency DECAY. EREMACAUSIS. 233 of the oxygen to combine with those elements. A perfect equalisation of this tendency, therefore, can only ensue when the elements, by combining with oxygen, have formed such products as are totally incapable of absorbing any additional amount of oxygen. It is only then that the attractions of the elements of organic substances attain a perfect equilibrium with those of oxygen. Fermentation or putrefaction represents the first stage of the resolution of complex atoms into more simple com- binations : the process of decay completes the circulation of the elements by transposing the products of fermentation and putrefaction into gaseous compounds. Thus the elements constituting all organised beings, which previously to par- ticipating in the vital process were in the forms of oxygen compounds, their carbon and hydrogen, reassume the form of oxygen compounds. The process of decay is a process of combustion taking place at the common temperature* in which the products of the fermentation and putrefaction of plants and animal bodies combine gradually with the oxygen of the atmosphere. No organised substance, no part of any plant or animal, after the extinction of the vital principle, is capable of resisting the chemical action of air and moisture ; for all the power of resistance which they temporarily possessed as the bearers of life, as the seat of the vital manifestations, completely ceases with the death of the organism ; their elements fall again under the unlimited dominion of the chemical forces. The clearing of the primeval forests of America, facilitating the access of air to that soil, so rich in vegetable remains, alters gradually, but altogether, its constitution : after the lapse of a few years no trace of organic remains can be found in it. The soil of Germany, in the time of Tacitus, was * In order to avoid the ambiguity attached to the word decay, from its being in vernacular language applied to several processes which it is desir- able to distinguish, the author proposed to substitute the term EREMA- CAUSIS, and this has been very generally adopted in scientific treatises, being a convenient mode of expressing the relation of decay to ordinary combustion. 234 LETTEES ON CHEMISTRY. covered with a dense, almost impenetrable, forest ; it must at that period have exactly resembled the soil of America ; but all the products of vegetable life in those primeval forests have completely vanished from our perceptions. The innumerable millions of crustaceous and other animals, whose remains form extensive geological formations and mountains, have, after death, passed into a state of fer- mentation and putrefaction, and subsequently, by the continuous action of the atmosphere, all their soft parts have been transposed into gaseous compounds, and their shells and bones, their indestructible constituents, alone remain, to furnish evidence of the past existence of life, continually extinguished, and continually reproduced. It is only in localities, under peculiar circumstances, where the access of oxygen was limited or altogether precluded, that we still find distinct remains of primeval vegetables in a state of retarded or impeded decay, as for example, in beds of turf and brown coal. The presence of water and a suitable temperature are indispensable conditions of the oxidising process of decay, just as they are necessary to putrefaction and fermentation. Perfect dryness, or a temperature below the freezing point, suspends all processes of decay and fermentation. The transmission of decomposition from one particle to another presupposes a change of place ; it requires that the particles should possess mobility, or the power of free motion, and this is imparted to them by the presence of water. In decay it is more especially a certain elevated tempera- ture which increases the aptitude of the elements of organic substances to combine with the oxygen of the atmosphere. A great number of organic bodies, when in a moist state, are capable of absorbing oxygen, whilst many, and indeed most of them, are per se entirely deficient in this pro- perty. If we place wet hay, or moistened fragments of wood, in a vessel filled with atmospheric air, all the properties of the contained air become in a very short time completely altered. EREMACAUSIS. BLEACHING. 235 If a lighted splinter, which of course would burn in atmospheric air, is introduced after the lapse of two or three hours, its flame will be immediately extinguished. The air confined in the vessel, if examined, will be found to have lost all its oxygen, and to have acquired an equal volume of carbonic acid gas. If a fresh supply of atmospheric air is made to replace this, the same process again occurs, all the oxygen becomes converted into carbonic acid. Exactly the same result would have been attained, had we burned the hay or wood in the confined air. In the process of bleaching in the open air, or, as it is called, grass-bleaching, we have the process of decay applied to an important purpose in the arts upon a large scale. Linen or cotton textures consist of ordinary woody fibre, more or less coloured by extraneous organic substances, which were either contained in the plant whence the fibre has been derived, or have become mixed with it during the processes of preparation. When linen or cotton fabrics are moistened with water and exposed to the light of the sun, a slow process of com- bustion, or decay, immediately begins upon the whole surface ; the oxygen of the atmosphere in immediate contact with the linen or cotton is incessantly converted into carbonic acid. The weight of the fabric diminishes every second, precisely because it is in a state of combustion j all the colouring matters gradually disappear, and with them a considerable amount of woody fibre, their elements being converted into oxygen compounds. If this action of air and light upon the linen or cotton continues for a considerable time, these substances lose their cohesion and become converted into a matter similar to that used in the manu- facture of paper, and this matter still continues to decay as long as the essential condition of this change, that is, the absorption of oxygen, continues. The nitrogenous constituents of plants and animals com- port themselves towards oxygen in a manner precisely similar to the behaviour of the non-nitrogenous principle we have spoken of; namely, woody fibre. Fresh meat, as well as 236 LETTERS ON CHEMISTRY. the first products of the decomposition of the nitrogenous constituents of plants in fermentation, that is, beer-yeast, or wine-yeast, withdraw oxygen from atmospheric air, and, like woody fibre, yield in return an equal volume of carbonic acid. When the Cemetery of the Innocents at Paris was removed from the interior of the town to the outside of the barriers, the buried corpses, which had accumulated to a depth of sixty feet, were found to a great extent apparently con- verted into fat. The substance of the skin, muscles, cellular tissue, and tendons, all the soft parts, and even the bones, had completely disappeared, leaving only the fat, which resisting longest the influence of decay, remained in the form of margaric acid. This human fat was employed to the extent of many tons by the soap-boilers and tallow- chandlers of Paris, for the manufacture of soap and candles. If meat be suspended in running water, or buried in moist earth, nothing of it will remain after the lapse of some time, except the fat which it contains. All substances susceptible of decay, when in a moist state, and exposed to the air and light at the common temperature, undergo precisely the same change as they would if exposed to a red-heat, in a dry state j that is, they absorb oxygen, they undergo combustion. Alcohol, one of the products of the fermentation of saccharine vegetable juices, is altogether incapable of under- going the process of decay; when exposed to the air, whether in its pure state or mixed with water, it evaporates without combining with oxygen. Alcohol is readily inflam- mable at a higher temperature, and in burning is resolved into carbonic acid and water. It is obvious that its elements have a powerful affinity for oxygen ; the high temperature is, however, a necessary condition of the manifestation of this affinity. Hydrogen gas and many other inflammable substances are, in this respect, precisely similar to alcohol ; their affinity for oxygen manifests itself only at certain high temperatures. EREMACAUSIS TRANSFERRED. 237 In the process of decay it has been likewise observed that a substance undergoing this state of elementary transposition exercises a remarkable influence upon the particles of an adjacent substance, which per se would not be capable of passing into the same state of change, decay, or trans- position. Many substances, when in contact with another in a state of decay, manifest, at common temperatures, an affinity for oxygen ; that is, they enter into combination with this element, at this low temperature, whilst under other cir- cumstances such a combination can only be effected by a far higher degree of heat. The state of active absorption of oxygen, the combustion of the decaying substance, is transmitted to the particles of other substances in contact with it ; they assume its charac- teristic state of activity : they behave as if they formed part of the decaying body, and their combination with oxygen is effected in a manner not further explicable, just as it is by heat. Contact with a substance, itself undergoing the process of decay, is the chief condition of decay for all organic substances which do not possess the power of com- bining with oxygen at common temperatures. In consequence of the ensuing combination of its elements with oxygen, the temperature of the decaying substance rises above that of the suiTounding medium ; but great as the influence is which heat exercises in accelerating the process, it is not in this, as in other chemical processes, the cause of the mani- festation of the affinity for oxygen. If, in a vessel filled with common atmospheric air, to which a certain amount of hydrogen gas has been added, a linen bag be suspended, filled with wet saw-dust, vegetable mould, &c., the process of decay will continue just as it would if they were exposed to the open air. They will convert the surrounding oxygen into carbonic acid. But what is very remarkable in this case, the hydrogen also participates in the process it undergoes decay ; that is, from being in contact with decaying substances, it acquires the power of com- bining with oxygen at the common temperature. If there 238 LETTERS ON CHEMISTRY. be a sufficient amount of oxygen present, all the hydrogen gas is converted into water. Other inflammable gases, both simple and compound, are affected under these circumstances in exactly the same manner as hydrogen. The vapour of alcohol, for example, when in a vessel containing wood or other substances in a state of decay, absorbs oxygen from the atmosphere, and becomes transformed into aldehyde, and subsequently into acetic acid, which, upon assuming a fluid state, is withdrawn from the further influence of the oxygen. It is upon this power of substances undergoing decay, to increase the attraction of all organic substances for oxygen, and especially the affinity of alcohol for this element, that a speedy process for acidifying alcohol was based, which is termed the " Schnellessigfabrikation," or " quick vinegar process." The transformation of fermented liquors into vinegar formerly required weeks, and even months, to accomplish, in consequence of the imperfect access of the air : we can now convert alcohol into vinegar in less than twenty-four hours ; and this is effected mainly by making spirits diluted with water trickle slowly through casks filled with wood shavings, and at the same time causing a slight stream of air to circulate through these shavings. This method exposes to the air a surface of alcohol capable of absorbing oxygen, by many thousand times more extensive than the old method ; and consequently the time which alcohol, under ordinary circumstances, requires for its acidification, is abridged in the same proportion. At the commencement of this process it is usual to add to the dilute spirit a small quantity of some substance containing matter capable of undergoing the process of decay, such as beer-wort, honey, vinegar, &c. ; but, after the lapse of a very short time, the surface of the wood-shavings passes into a state of oxidation, and from that moment effects the transformation of the spirit into vinegar without the further co-operation of extraneous decaying matter. The origin of nitric acid or nitrates (nitrification), and the NITRIFICATION. 239 occurrence of these salts in certain kinds of garden mould and fertile soil, in the earth floors or in the walls of cow- houses, stables, or other houses, and in the spring water of towns and villages, depends on the same general cause as the formation of acetic acid from alcoholic liquids. The nitric acid is produced from the ammonia, one of the ultimate products of putrefaction of animal, or rather of nitrogenous substances. When ammonia is in contact with decaying matters, and when lime or magnesia, and a certain amount of moisture are present, the elements of ammonia, its nitrogen and hydrogen, unite with the oxygen of the air to form nitric acid and water, and the acid forms salts, that is, nitrates, with the alkalies or alkaline earths. The crystalline salts which often effloresce on the walls of stables and cowhouses, and in places moistened with the liquid of sewers, are nitrates, usually nitrate of lime, a salt which deliquesces in moist air, and by the presence of which the walls become continually moist and damp. A great part of the nitre (nitrate of potash) used for the manufacture of powder in France, is obtained, in Paris, from the lower stones of the houses, which are constantly in contact with the liquids of the streets and drains. The lime of the walls is gradually dissolved by the nitric acid formed ; the walls lose their coherence and firmness ; hence the name of wall-corrosion (in German, Mauerfrass) given to this injurious formation of nitre.* In India, with its higher temperature, animal substances decay in moist air very quickly; and from the more complete combustion of the ammonia, there is formed a corresponding larger quantity of nitrates. The application of our knowledge respecting the pheno- mena attendant upon decay, to the manufacture of beer and * The potash of the nitre is generally derived from bricks, and even the mortar contains some potash, which gradually decomposes the nitrate of lime, aided by the superior crystallising power of nitre, so that the latter salt is formed. But generally, in order to obtain all the nitric acid as nitre, potash must be added to the liquid obtained from the scrapings of the walls by lixiviation with water. W. Gr. 240 LETTERS ON CHEMISTRY. wine, is easy and obvious. The property of beer and wine to be converted into vinegar when in contact with the air, depends invariably upon the presence of foreign matters which transmit their own inherent aptitude to absorb oxygen to the particles of alcohol in contact with them. By removing completely all such substances from wine and beer, these lose altogether the property of acidifying, or of being converted into vinegar. In the juice of grapes poor in sugar there remains, after the completion of the process of fermentation that is, after the resolution of the sugar into carbonic acid and alcohol a considerable amount of nitrogenous constituents, retaining the same properties which they possessed in the juice pre- vious to fermentation. This does not happen with the juice of the grapes of southern climates. These grapes are rich in sugar, and a considerable amount of this substance remains undecomposed after all nitrogenous matters have completely separated in an insoluble state, as yeast. Such wines alter very little when exposed to the air : the red wines of this kind, however, acidify because their colouring matter is of ready mutability, and performs, when in contact with the air, the part of the nitrogenous constituents. The nitrogenous constituents of the grape-juice which remain in wine, after fermentation, are those ferments, or exciters of fermentation in the sugar, of which I have already spoken. After the complete transformation of the sugar, they exercise upon the alcohol exactly the same effect as the decaying wood they are "the exciting causes of the ensuing process of acidification. The affinity of these substances for oxygen is very power- ful ; during the short space of time necessary to transfer wine from one cask into another, they absorb oxygen from the air, and induce a state of acidity in the wine, which goes on irresistibly if it be not checked by artificial means. It is well known that this check is practically effected by sul- phuration. A piece of sulphur is burned in the cask destined to receive the wine, the contained air is thus deprived of its oxygen, and an amount of sulphurous acid is MANUFACTURE OF WINES. 241 formed equal to the volume of the oxygen. This newly- formed sulphurous acid is rapidly absorbed by the moist internal surface of the cask. Sulphurous acid possesses a stronger affinity for oxygen than the exciters of acidification in the wine. The acid is gradually diffused from the internal surface of the cask through the wine, and withdraws from those substances, as well as from the wine itself, all the oxygen they have absorbed from the atmosphere, and thus reconverts the wine into the state in which it existed pre- viously to being transferred into the new cask. The sulphurous acid in this process becomes converted into sulphuric acid, and exists as such in the wine. When the wine is stored up in casks to ripen, a constant, although very slow, diffusion of air takes place through the pores of the wood, or, what comes to the same thing, the wine is incessantly in contact with a minute amount of oxygen; by means of which, after the lapse of a certain time, the entire quantity of the exciters of acidification, that is, the nitrogenous substances present in the wine, oxidise and separate in the form of a sediment or dregs, termed under-yeast, or sedimentary yeast. The separation of yeast from wine or beer, during the fermentation of grape-juice or of worts, takes place in con- sequence of the absorption of oxygen, or, in other words, is a process of oxidation, occurring in the fermenting liquid. The nitrogenous constituent of barley is in its primary state insoluble in water, but in the process of malting, or whilst the grain is germinating, it becomes soluble in water, it assumes the same condition or nature which belongs to the nitrogenous constituent of grape-juice originally. Both these substances lose their solubility in wine, or in beer, by absorbing oxygen. According to analyses in which we may confide, made with regard to this point, wine-yeast and beer-yeast are far richer in oxygen than the nitrogenous substances from which they are derived. As long as any particles of sugar, in a state of fermentation, are present in the fluid together with these nitrogenous matters, the fluid itself supplies the oxygen required for 242 LETTERS ON CHEMISTRY. their transformation into yeast by the decomposition of a small amount of the sugar or of water. This oxidising process within the fluid itself, which causes the nitrogenous constituents to become insoluble, ceases with the disappear- ance of the sugar ; but it is renewed if the fluid is recon- verted into a fermenting state, by the addition of new portions of sugar, and it ensues also when the surface of the fluid is exposed to the free access of the atmosphere. In the latter case the separation of the nitrogenous constituents is effected by the atmospheric oxygen, and is thus a conse- quence of their decay or slow combustion. I have already stated that the presence of nitrogenous matters in alcohol causes the transformation of the alcohol into acetic acid when there is a sufficient supply of air ; now it is owing to the inequalities in their relative affinities for oxygen, that during the maturation of wine in the store- house, when the access of air is extremely limited, that the nitrogenous substances alone oxidise, and not the alcohol. In open vessels, under these circumstances, the wine would become converted into vinegar. The preceding remarks render it obvious that if we pos- sessed any means of preventing the transformation of alcohol into acetic acid we should be able to preserve wine and beer for an unlimited period, and to bring those liquors into a state of perfect maturity in a very short time ; for, under such circumstances, all those substances which cause wine and beer to acidify would become insoluble by combining with oxygen, and separate from the liquid, and with their perfect removal the alcohol present would altogether lose the property of absorbing oxygen. Experimental art has discovered a means of accomplishing this purpose perfectly. It consists in keeping the fluid at a low temperature when undergoing fermentation. The method, based upon this principle, and employed in Bavaria, is one which the most perfect theory could scarcely have surpassed in certainty and simplicity, and it seems impos- sible to devise one more in accordance with science. The transformation of alcohol into acetic acid by contact BAVARIAN BEER. 243 . with a substance in a state of decay occurs most rapidly at a state of temperature of 95 Fahrenheit. At lower temperatures the affinity of alcohol for oxygen decreases, and at from 46 to 50 Fahrenheit no combination with oxygen takes place under these circumstances, whilst the ten- dency of nitrogenous substances to absorb oxygen at this low temperature is scarcely diminished in any perceptible degree. It is, therefore, obvious that if wort be fermented in wide, open, and shallow vessels, as is done in Bavaria, which afford free and unlimited access to the atmospheric oxygen, and this in a situation where the temperature does not exceed 46 to 50 Fahrenheit, a separation of the nitrogenous constituents, i. e. the exciters of acidification, takes place simultaneously on the surface, and within the whole body of the liquid. The clearing of the beer is the sign by which it is known that these matters are separated. A more or less perfectly complete removal of these nitrogenous sub- stances, however, according to this method of fermentation, depends upon the skill and experience of the brewer. It may be easily conceived that an absolutely perfect separation of them is attained only in rare and extremely happy instances. Nevertheless, the beer obtained in this manner is invariably far superior in quality and stability to that brewed according to the common method. The exceedingly favourable influence which the adoption of this principle must exercise upon the manufacture of wine is indisputable. It is too evident to admit of a doubt that it will lead to the adoption of a more rational method than has hitherto been employed. Wine prepared by this method will, of course, bear the same relation to the wine prepared in the ordinary way, that Bavarian beer bears to common beer, in the fabrication of which the same amount of malt and hops has been employed. In the shortest possible time the same quality, the same maturity, may be attained by the wine which, under ordinary circumstances, would result, only after long and protracted storing. If it be borne in mind that the K 2 244 LETTERS ON CHEMISTRY. period for the manufacture of wine is the end of October, just at the cool season which is peculiarly favourable to the fermentation of beer, and that no other conditions are necessary to the vinous fermentation than a cool cellar, and open, wide fermenting vessels, and further, that under all circumstances the danger of acidification is much less with wine than with beer, it is evident that the best success may confidently be expected from the application of this method.* It must not be forgotten, that wine contains a much smaller proportion of nitrogenous matters after fermentation, than beer-worts, and that a much more limited access of air is required for its complete oxidation and separation in an insoluble form. The method employed at most places on the Rhine proceeds upon principles the very reverse of this. The wine is left to ferment, not in cool cellars, but in rooms, situate^ much too * One of the most intelligent agriculturists and wine-growers of the Grand Duchy of Baden, Baron von Babo, remarks, in a letter to me, dated April, 1843, "With respect to the application of the Bavarian method of fermentation to the manufacture of my red wine last autumn, I am happy to inform you that it again answered excellently. Our wine-makers cannot understand the matter, clear and obvious as it is, that the method which it is universally acknowledged yields most excellent results in the manufacture of beer, should be as advantageously applied to making wine. " An experiment made with red wine in the autumn of 1841, by the same nobleman, had afforded the same favourable results, especially as to the colour of the wine. Before these successful experiments it might have been thought that red wine was the rock upon which this method would founder, but we are now assured of its universal adaptation to the manufacture of wines. Experiments on the great scale, made in 1846 on the Johannis- berg, with six casks of juice, each of 1200 bottles capacity, most kindly granted by Prince Metternich, under the direction of the experienced wine- grower Herr Heckler, have proved, that the access of air during the fer- mentation exercises an essentially favourable influence on the quality of the wine. In each of the casks a hole of twelve inches square was cut at the bung, and it appeared, that an opening of six inches square, covered with coarse canvass, answers perfectly, and that the wine thus fermented had an evidently better quality than that fermented with the fermenting pipe, air being excluded. Exactly similar results were obtained by Dr. Crasso, when he fermented the juice in casks, the tops of which -were taken off, and used as loose covers during the process. (Annalen der Chemie und Pharmacie, lix. p. 360). In other experiments, in which the wine fermented in open vats, it lost its bouquet and became flat. IMPROVEMENTS IN WINE MAKING. 245 high and too warm ; the access of air is completely precluded during the process of fermentation by tin-plate tubes, confined with water. These tubes certainly exercise an injurious effect upon the quality of the wine ; they are, in every respect, futile the invention of some idle brain ; they serve no object, and yet they are used by people who imitate others, without assigning any reason for doing so. 246 LETTERS ON CHEMISTRY LETTER XX. Boiling checks fermentation Preservation of meat, fruits, &c., by Appert's process Effect of the introduction into the system of putrescent matters Poisoning from dissection : from bad sausages, &c. Antidotes to these poisons Danger of bad meat. THE property of organic substances to pass into a state of fermentation and decay, in contact with atmospheric air, and, in consequence, to transmit these states of transmutation to other organic substances, is annihilated in all cases, without exception, by heating to the boiling point. This is certainly the most striking and evident proof that the ready mutability of these substances is connected with a certain mode of arrangement of their component atoms. We need only consider the coagulation of albumen by heat, to under- stand the manner in which heat acts in producing this effect. Most ferments have a constitution analogous to that of albumen, and, at a higher temperature, pass into a new state. When sweet almonds are blanched, and allowed to remain even only a few seconds in boiling water, their power of acting upon amygdaline is completely annihilated. Amygdaline dissolves without alteration in almond-milk which has been heated to the boiling point. Malt altogether loses, by boiling, its property of converting starch into sugar. A watery infu- sion of beer-yeast, in which cane-sugar instantly passes into grape-sugar, and the juice of diseased potatoes, in which the substance of the cells of sound ones is disintegrated and rendered soluble, both lose, when heated to boiling, these properties entirely. Fresh animal milk, as is well known, coagulates, after being kept for two or three days, into a gelatinous mass. If fresh milk be heated daily to the boiling point it may be BOILING CHECKS FERMENTATION. 247 preserved for an indefinite period. Grape-juice, so readily mutable, and every fluid susceptible of fermentation, is affected in the same manner ; when heated to the boiling point all fermentation in them ceases. Beer-wort, after boiling, requires the addition of yeast, that is, an extraneous substance already itself in a state of decomposition, in order to ferment in the shortest possible time. It is obvious that if that particular state into which an organic substance is brought by contact with the atmos- phere, although this contact may have been but for an instant, be destroyed by a high temperature, and oxygen (the only cause of its re-appearance) from the time of its boiling be excluded, these substances must, for an unlimited period, retain all the properties they possessed at the moment of boiling. Matter per se has no inherent power of mobi- lity ; without the influence of some external force upon the atoms, none of them change their place, none alter their properties. If a bottle be filled with grape-juice and made air-tight, and then kept for a few hours in boiling water, or until the contained grape-juice has become throughout heated to the boiling point, the minute amount of oxygen contained in the air which entered the flask with the grape-juice becomes absorbed during the operation by the constituents of the juice, and thus the cause of further perturbation is removed. The juice does not now ferment, but remains perfectly sweet until the flask is again opened, and its contents brought into contact with the air. From this moment the same alteration begins to manifest itself which fresh juice undergoes ; after the lapse of a few hours the contents of the flask are in full fermentation, and this state may be again interrupted and suspended, as at first, by repeating the boiling. The knowledge of these properties, which are equally possessed by all other organic substances, without exception, has given rise to the most beautiful practical applications of them. Whilst, in former times, during long voyages, mariners were confined to salt and smoked meats, which, in the long run, always proved injurious to the health of the crew and 248 LETTERS ON CHEMISTRY. the passengers, and thousands of human beings lost their lives from the want of fresh aliments, which were even more essential in sickness, these dangers and discomforts become more and more rare at the present day. This is certainly one of the most important contributions to the practical benefit of mankind ever made by science, and for this we are indebted to Gay-Lussac. At Leith in the neighbourhood of Edinburgh, at Aberdeen, at Bordeaux, Marseilles, and in many parts of Germany, establishments of enormous magnitude exist, in which soup, vegetables, animal substances, and viands of every description are prepared and sent to the greatest distances. The pre- pared aliments are enclosed in canisters of tinned iron plate, the covers are soldered air-tight, and the canisters exposed to the temperature of boiling water. When this degree of heat has penetrated to the centre of the contents, which it requires about three or four hours to accomplish, the aliments have acquired a stability which, one may almost say, is eternal. When the canister is opened after the lapse of several years, the contents appear just as if they were only recently enclosed. The colour, taste, and smell of the meat and vegetables are completely unaltered. This valuable method of preparing food has been adopted by many persons in my neighbourhood and other parts of Germany, and has enabled our housewives to adorn their tables with green vegetables in the midst of winter, and with dishes at all times which otherwise could be obtained only at particular seasons. This method of preserving food will become of the greatest import- ance in provisioning fortresses, since the loss incurred in selling off old stores, and replacing them by new, especially with respect to meat, ham, &c., is far more considerable than the value of the tin canisters, which, moreover, may be repeatedly employed after being carefully cleansed. When we compare the phenomena of putrefaction and fer mentation with the processes in the living animal body, it becomes very probable, that a number of effects, which we are accustomed to refer to peculiar vital influences, are deter- mined by the same causes on which fermentation and putre- FOOD IS FERMENTESCIBLE. 249 faction depend. These analogies have been noticed and pointed out for centuries by philosophers and physicians ; but even now many of the latter class consider, in opposition to the view here developed, certain vital actions or manifestations of vitality as the causes of putrefaction and fermentation. It has been stated above that the constituents of the mass of the body, albumen, fibrine, membranes, skin, and caseine, when putrescent, exert a peculiar influence on many sub- stances, the visible result of which is a chemical change in the substance brought in contact with these compounds. It is further an established fact, that the products derivable from the substances thus acted on are not always the same, but vary with the state of decomposition of the ferment or exciting body. But if a change of position and arrangement in the par- ticles of animal substances can exert, out of the body, a very decided influence on a number of organic compounds ; if the latter, when in contact with these ferments, are decomposed, and new compounds, less complex, formed of their elements, and if we reflect that to the class of fermentescible substances belong all the matters which constitute the various articles of the food of men and animals, then we can hardly doubt that this cause of change plays an important part in the vital pro- cesses, and has a chief share in producing the changes which the constituents of the food undergo, when they are con- verted, in the body, into fat or into tissues forming parts of organs, or in the formation of the secretions and excretions, such as milk, bile, urine, &c. We know, indeed, that in all parts of the living animal body a change of matter is going on at every moment of time ; that living parts are expelled; that their constituents, albumen, fibrine, membranes, and all the rest, whatever their names, arrange themselves in the moment of their separation from the living tissue, and, subsequently, into new products. Our expe- rience compels us to conclude that by this change of quality and composition itself, at every point where it occurs, and according to its force and direction, a parallel and correspond- ing change is effected in the composition and quality of all 250 LETTERS ON CHEMISTRY. the constituents of the blood, or the food, which come into contact with them, and that, consequently, the change of matter is a chief cause of the changes which the food under- goes, and also a condition of the process of nutrition. We know that with every change effected by a cause of disease in the process of transformation of an organ, of a gland, or of a constituent of these, the action of that organ on the blood conveyed to it, that is, the quality of its secretion, is likewise altered ; that the action of a multitude of remedies depends on the share which they take in the change of mat- ter ; and that, in many cases, this action of remedies, by changing, accelerating, retarding, or arresting the direction or the force of the agency which operates in the organ, exerts an influence on the quality of the blood. Finally, by a knowledge of the causes of the origin and propagation of putrefaction in organic atoms, the question concerning the nature of many contagions and miasms becomes capable of a simple solution, and may be reduced to the following : Are there facts which prove that certain states of trans- formation or putrefaction in a substance are likewise propa- gated to parts or constituents of the living animal body ; that, by contact with the putrescent matter, the same or a similar condition is produced on such parts, as that in which the particles of the putrescent body are ? This question must be answered decidedly in the affirmative. It is a fact, that dead bodies in dissecting-rooms frequently pass into a state of decomposition which is communicated to the blood in the living body. The slightest cuts with the scalpels used in dissecting often cause a very dangerous and even fatal disease.* The observation of Magendie, that putrid blood, brain, bile, or pus, when laid on fresh wounds, produce in animals vomiting, languor, and death after a shorter or longer interval, has not yet been contradicted. See Appendix, No. 3. * Cases in which anatomists fall victims to this frightful kind of poison- ing are not rare ; as in the recent melancholy examples of Dr. Kolletschka in Vienna, Dr. Bender in Frankfort-on-the-Maine, and many others. PROPAGATION OF CONTAGIOUS DISEASES. 251 Further, it is a fact, that the use of various articles of food, such as flesh, ham, sausages, if in a certain state of decom- position, is followed, in healthy persons, by the most danger- ous and even fatal symptoms. See Appendix, No. 4. These facts prove that an animal matter, in a certain state of decomposition, is capable of exciting a morbid action in the body of healthy individuals. Now, since by the term, products of diseased action, nothing else can be meant than parts of constituents of the living body which are in a state of change in form and quality different from the normal one, it is evident, that, so long as this state continues, and the change is not completed, the disease may be communicated to a second or third individual, and so on. Besides, when we consider, that all those substances which destroy the communication or arrest the propagation of contagions and miasms, are likewise such as arrest all pro- cesses of putrefaction or fermentation ; that under the influ- ence of empyreumatic bodies, such as pyroligneous acid, which powerfully oppose putrefaction, the diseased action in malig- nant suppurating wounds is entirely changed ; that, in a number of contagious diseases, especially in typhus, ammonia, free or combined, is found in the exposed air, in the liquid and solid excreta, (in the latter as ammonio-phosphate of magnesia), it seems impossible any longer to entertain a doubt as to the origin and propagation of many contagious diseases. Finally, it is an observation universally made, and which may be regarded as established, " that the origin of epidemic diseases may often be referred to the putrefaction of great masses of animal and vegetable matters ; that miasmic dis- eases are found epidemic, where decomposition of organic substances constantly goes on, in marshy and damp districts. These diseases also become epidemic, under the same circum- stances, after inundations ; and also in places where a large number of persons are crowded together with imperfect ven- tilation, as in ships, in prisons, and in besieged fortresses." (Henle, Untersuchungen, p. 52 also p. 57.) But in no case may we so securely reckon on the occurrence of epidemic 252 LETTERS ON CHEMISTRY. diseases, as when a marshy surface has been dried up by continued heat, or when extensive inundations are followed by intense heat. See Appendix, No. 5. Hence, according to the rules of scientific research, the conclusion is entirely justified, that, in all cases, where a putrefactive process precedes the occurrence of an epidemic or contagious disease, or where the disease can be propagated by means of solid, liquid, or gaseous products of diseased action, and when no other cause for the disease can be disco- vered, the substances which are in a state of transformation are in virtue of that state, to be regarded as the proximate causes of the disease. The well-informed and attentive physician has been long aware that the difference between good and wholesome food, and that which is bad, which latter is justly regarded as the cause of many diseases, depends, not on the nature of the food, but on a certain quality or state of it, which, in the case of flesh, for example, can often be referred to a diseased state of the animal from which it was taken. He knows that the useful and beneficial effects of a proper ventilation on the preservation of health, may be often attained, in the chamber of the sick, for example, by the evaporation of small quantities of nitric acid (not of chlorine, which, in most cases, has an injurious, or at least an irritating, effect), or by the burning of a little sulphur ; by means of substances, therefore, which we know can destroy noxious gases, or put an end to their state of decomposition. THEORIES OF FERMENTATION. 253 LETTER XXI. Theory which ascribes fermentation to Fungi refuted Characters of Yeast Putrefaction not caused by Animalculse ; but decay is hastened by them Parasitic theory of Contagion refuted Scabies Muscardine Limits of Vital and Physical Forces. SOME philosophers, and especially many physiologists and medical men, have adopted a peculiar view concerning the causes of the appearances, so remarkable in themselves, which occur after the death of plants and animals, and which effect their resolution into inorganic compounds, and their disappearance from the earth's surface. This opinion would be hardly worth mentioning, were it not that it has furnished a foundation for entirely fallacious ideas concern- ing the essence of the vital processes in general, and especially of many pathological conditions, and the causes of certain diseases. These philosophers regard fermentation, or the resolution of higher or more complex organic vegetable atoms into less complex compounds, as the effect of the vital manifestations of vegetable matters ; and putrefaction, or the same change in animal substances, as being determined by the develop- ment or the presence of animal beings. They assume, as a natural consequence of this view, that the origin of miasmic or contagious diseases, in so far as referable to the presence of putrefactive processes, must be ascribed to the same or similar causes. The most obvious and important considerations in support of this view of fermentation are derived from observations made on the alcoholic fermentation, and on the yeast of beer and of wine. The microscopic researches of physiologists and botanists have demonstrated that beer or wine yeast 254 LETTERS ON CHEMISTRY. consists of single globules, often strung together, which possess all the properties of living vegetable cells, and resemble very closely certain of the lower families of plants, such as some fungi and algae. In fermenting vegetable juices, we observe, after a few days, small points, which grow from within outwards ; and these have a granular nucleus, surrounded by a transparent envelope. In agreement with these observations, chemical examina- tion has proved, that the cell walls of the globules of beer yeast consist of a non-nitrogenous matter, having the composition of cellulose or woody fibre, which remains undissolved, when the yeast, after being well washed with water, is treated with weak caustic alkalies. The alkaline solution takes up a substance, which contains all the nitrogen of the yeast globules, and which, in chemical character and in composition differs little, and that chiefly in the propor- tion of oxygen, from the gluten of grain. After incineration, yeast leaves an ash, entirely identical, in regard to its constituents, with the ash of the gluten of the cereals. It has also been particularly pointed out, that in the fermenting beer-wort (infusion of malt), the formation and separation of the yeast cells keep pace with the production of carbonic acid and alcohol. When all the sugar is decom- posed, no more yeast is formed. The yeast contains the nitrogenous constituent of the malt or barley, of which, when a certain amount of sugar is present, only traces are found in the liquid after fermentation. The simultaneous appearance of the yeast cells, and of the products of decomposition of the sugar, is the chief argument in support of the opinion, that the fermentation of sugar is an effect caused by the vital process, a result of the development, growth, and propagation of these low vegetable structures. If, by the term vital action, we understand the power of a germ or of a seed to take up certain substances from with- out, and to make them parts of itself; then the formation of the yeast cells in fermenting wort is, beyond all doubt, a proof of the existence of a vital action. The cell walls are, THEOEIES OF FERMENTATION. 255 in all probability, formed at the expense of a certain portion of sugar, since they consist of a compound which stands higher in the organic scale than sugar, and never appears in a crystalline form. The contents of the cells have been derived from the gluten of the malt, and contain, among other things, parts, spores, or germs, which, if introduced into fresh wort, determine the formation and development of new cells. But if the development increase, and propagation of these vegetable cells or tissues be the cause of fermentation, then, in every case where we observe this effect, we must suppose that the causes or conditions, namely, sugar, from which the cell walls are produced, and gluten, which yields their con- tents, are both present. Now the most remarkable fact among the phenomena of fermentation, and that which must chiefly be kept in view in the explanation of the process, is this : that the ready- formed cells, after being washed, effect the conversion of pure cane-sugar into grape-sugar, and its resolution into a volume of carbonic acid and a volume of the vapour of alcohol, and that the elements of the sugar are obtained without any loss in these new forms ; that, consequently, since 3 Ibs. of yeast, considered in the dry state, decompose 2 cwt. of sugar, a very powerful action takes place, without any notable consumption of matter for the vital purpose of forming cells. If the property of exciting fermentation depended on the development, propagation, and increase of yeast cells, these cells would be incapable of causing fermen- tation in pure solution of sugar, in which the other conditions necessary for the manifestation of the vital properties, and especially the nitrogenous matters necessary for the production of the contents of the cells, are absent. Experiment has proved, that in this case the yeast cells cause fermentation, not because they propagate their kind, but in consequence of the decomposition of their nitrogenous contents, which are resolved into ammonia and other products ; that is, in consequence of a decomposition which is exactly the opposite of an organic formative process. 256 LETTERS ON CHEMISTRY. The yeast, when brought into contact successively with new portions of sugar, loses, by degrees, entirely its power of causing fermentation, and at last nothing is left in the liquid but its non-nitrogenous envelopes or cell walls. Hence it follows, that the cause of the resolution of the sugar into new forms cannot properly be sought for in a process of vegetation, because this effect takes place without the yeast cells being reproduced as a vegetable tissue, and under circumstances which destroy their power of propaga- tion and increase. It is obvious, that the phenomena depend on the presence of an action, or a state of change, which continues even when the conditions necessary to the formation of cells are excluded. Further, if we consider that the action of yeast is not confined to sugar alone ; that other bodies, of totally different composition, undergo a similar decomposition in contact with yeast; that tannic acid in a fermenting saccharine liquid passes into gallic acid ; the malic acid of malate of lime into succinic acid, acetic acid, and carbonic acid ; that an animal membrane, or the albuminous part of sweet almonds, (substances differing in composition from gluten), when putrescent, produce the same changes as yeast : it follows, that the peculiar action of yeast depends on a more general cause, and not on the sugar; and that the resolution of sugar into alcohol and carbonic acid does not depend on a constant quality in the yeast. Observation shows, that beer yeast, left to itself, very quickly loses its power of exciting the alcoholic fermentation. That power is lost when the yeast is rubbed on a levigating stone till all organic structure is destroyed ; but this does not annihilate its power of decomposing organic substances in general. For it now acquires the property of converting sugar into lactic acid, and the lactic acid of lactate of lime into butyric acid, mannite, hydrogen, and carbonic acid. And these are effects which take place without any forma- tion of cells or vegetable tissues. All this proves that it is neither the organic form, nor the chemical composition of the yeast, but merely a certain FUNGI NOT ALWAYS FORMED. 257 state of the nitrogenous contents of the yeast cells, which must be regarded as the cause of the decomposition of sugar in the alcoholic fermentation. The fermentation of grape-juice and of beer-wort is no isolated phenomenon ; these are individual cases out of a class including many others. The alcoholic fermentation, in so far as it is accompanied by the formation or decomposition of fungi, is distinguished from other kinds of fermentation, in which no vegetable tissues are observed, in this, that the products of the decomposition of gluten possess, in addition to their chemical properties, certain vital properties. Gluten, vegetable albumen, and the vegetable caseine of vegetable juices, cause fermentation, because they enter into decom- position ; their action depends on the state of change of form and quality of their elementary molecules. As they gradually change and are separated, they assume, in con- sequence of other secondary causes, the forms of a low vegetable structure, the vital properties of which depend on a transition state, and disappear on its completion or ter- mination. The yeast cell, as a fungus or alga, has no independent existence. As a single or individual case, the fermentation of sugar requires no special explanation, since no other expression can be given to the process than that developed in the preceding letters. The sugar is resolved into alcohol and carbonic acid in consequence of a disturbance of the equi- librium in the attractions of its elements, and this disturbance is caused by a substance whose elementary particles are in a state of motion. Of the known processes of fermentation, only the alcoholic fermentation has been hitherto studied with any degree of accuracy ; and we have observations (those of Doepping, Struve, and Karsten,) which prove that sugar may be resolved into alcohol and carbonic acid without the appearance of the fungi alluded to. In many other fermentations the constant occurrence of such vegetable forms has not been observed. There is not the remotest proof of a real connection between the vital properties of these fungi and the formation of the 258 LETTERS ON CHEMISTRY. products of fermentation ; and no one has even attempted to connect the two phenomena as cause and effect, and to explain how or in what manner a plant can cause the resolution of sugar into alcohol and carbonic acid. When we examine strictly the arguments by which this vital theoiy of fermentation is supported and defended, we feel ourselves carried back to the infancy of science. There was a time when men could not account for the origin of the lime of the bones, the phosphoric acid in them and in the brain, the iron in the blood, and the alkalies in plants ; and we now find it inconceivable that this ignorance should have been regarded, as it was, as a proof that the animal or vegetable organism possessed the power of creating iron, phosphorus, lime, and potash, by virtue of its inherent vital forces, out of food containing none of these substances. This convenient explanation naturally put an end to the inquiry as to their real origin, and arrested true investigation. Simple observation leads, in the examination of certain fermentative or putrefactive processes, to the fact of the presence of organised living beings, and without asking any further questions, the presence of these fungi, whose origin is perfectly unknown, is connected with the formation of the products of fermentation and putrefaction, as their cause. Because no other cause can be found (or rather, because no other cause has been sought for by the observers of the fact,) which explains the formation of these products, we are desired to ascribe it to a cause which is utterly incomprehensible. With respect to that theory which regards the putrefaction of animal matters as produced by microscopic animalculee, it may be compared with the idea entertained by a child, who explains the rapid fall and current of the Rhine through the numerous Rhine mills at Mayence, by supposing that the mill-wheels, by their force, urge the water downwards towards Bingen. Is it conceivable that the annihilation and destruction of plants and animals should be the effects of the agency of other plants and animals, which are themselves subject to the same processes of destruction ? PUTREFACTION NOT CAUSED BY ANIMALCULES. 259 If the fungus or mushroom be the cause of the destruction of the oak if the animalcule be the cause of the putrefaction of a dead elephant ; what then is the cause of putrefaction, after death, of the fungus 1 what is the cause of the putre- faction and decay of the dead animalcule ? They also ferment, decay, and putrefy, and finally disappear entirely? just as do the mighty tree and the gigantic animal ; and the final products are the same in all. It is impossible to adopt this opinion, when we reflect, that the presence of microscopic animals in putrescent substances is quite accidental ; that their appearance, in most cases, may be prevented by the exclusion of light ; that putrefaction and decay may go on without the least assistance from them ; that in a thousand cases, in putrescent urine, cheese, bile, or blood, no such animals whatever are observed ; and that in other cases, they appear for the first time, in a certain stage, long after fermentation has begun. To ascribe putrefaction to the presence of animalculse is as irrational as it would be to ascribe to the beetles whose food is derived from animal excreta, or to the mites in cheese, the state of decomposition of the excreta or of the cheese. The presence of animalcule, which are often found in prodigious numbers in putrefying matters, cannot in itself be considered wonderful, since these animals find there the conditions of their nutrition and development combined. Their appearance is not more extraordinary than the migration of salmon from the sea into rivers, or the growth of salt-plants in the vicinity of salt-works ; the only difference lies in our ability to trace the latter in their progress ; whilst the germs of the fungi, and the eggs of infusorial animalcule escape our notice, in consequence of their extreme minute- ness, and the ocean of atmosphere through which they are diffused. It is quite certain that in their presence putrefaction is exceedingly accelerated. Their nutrition presupposes the consumption of particles of the animal body for their own development. Its more rapid destruction must be the s 2 260 LETTERS ON CHEMISTRY. necessary consequence. We know that one single individual procreates many thousands in a very short time, but their growth and development are confined within definite limits ; when they have once reached a certain size, they no longer increase in bulk, whilst they continue at the same time to partake of nutriment. Then what becomes, we must ask, of the food which no longer augments their size 'I Must it not undergo in their organism a similar alteration to that which a piece of meat or bone undergoes in the body of a full-grown dog, the weight of which no longer increases ? We know positively that the food of the dog serves for the support of the vital processes, and that its elements receive in its organism the form of carbonic acid and urea ; which latter substance becomes rapidly resolved, after being eliminated from the organism, into carbonic acid and ammonia. This food, therefore, undergoes in the body the same alteration as if it had been burned in a stove ; that is, it is subjected to eremacausis, or decay. The same occurs in decaying animal substances ; they serve as nourishment for microscopic animalculse, in the bodies of which their elements deca} r . These animalcule die when their means of subsistence are exhausted, and their bodies putrefy and decay, and, perhaps, serve for the nourish- ment and development of other races of living beings. But the process is, and continues to be, one of combustion, in which the elements of the original body, before combining with oxygen, became parts of living beings, in which, there- fore, they form a series of intermediate compounds before they pass into the ultimate products of the process of decay. But the constituents of animals which enter into combina- tion with oxygen in the organism no longer belong to the living body. During the true putrefactive process, that is, the decomposition of animal substances with the exclusion of oxygen, gases are evolved (sulphuretted hydrogen, for instance), which exercise a deleterious influence, and speedily put a limit to the life of even the microscopic animalcutae. The excrements of man, while putrefying, never exhibit the presence of microscopic animalcuUe, whilst we find abundance OXYGEN PRODUCED BY INFUSORIA IN WATER. 261 of them in these excrements when in a state of decay. A wise arrangement of nature has assigned to the infusoria the dead bodies of higher orders of beings for their nourishment, and has in these animalculse created a means of limiting, to the shortest possible period, the deleterious influence which the products of dissolution and decay exercise upon the life of the higher classes of animals. The recent discoveries which have been made respecting these creatures are so extraordinary and so admirable, that they deserve to be made universally known. Count Rumford observed that cotton, silk, wool, and other organic substances, when exposed to the light of the sun under water, after the lapse of from three to four days gave rise to the evolution of pure oxygen gas. With the appearance of the first gas-bubbles the water assumes a greenish colour, and exhibits under the microscope the presence of an immense number of minute spherical animals, to which the green hue of the water is owing. No confervse or other microscopic plants, to which the evolution of oxygen could be ascribed, were perceived. These observations, made about seventy years ago, .have been rescued from oblivion by recent observations. In the salt-pans of the salt-works, of Rodenberg, in the electorate of Hesse, a slimy and transparent mass is formed, which covers the bottom to the depth of from one to two inches, and is everywhere interspersed with large air-bubbles, which ascend in great numbers through the supernatant fluid, when the pellicles enclosing them are torn by agitating the mass with a stick. Pfankuch upon investigation found the air enclosed in these bubbles to be such pure oxygen that a wood splinter, the flame of which has been just extin- guished, rekindles into a flame when immersed in it. This observation has been confirmed by Woliler. The microscopic investigation of the mass at the bottom of the pans proved that it consisted of living infusoria, chiefly of the species navicula and gallionella, such as occur in the siliceous fossil strata of Franzensbad, and in the paper-like formations of Friberg. After being washed and dried, the mass, upon 262 LETTERS OX CHEMISTRY. heating, evolved ammonia, and upon incineration left white ashes, consisting of the siliceous skeletons of these animal- culae, which preserved the original form of the animal so perfectly, that they looked like the original deposit only deprived of motion. About the same time, Messrs. Ch. and A. Morren, in the " Transactions of the Academy of Brussels " (1841), showed that water, with the co-operation of organic matters, evolves a gas containing as much as 61 per cent, of oxygen ; and that this phenomenon is to be ascribed to the presence of Chlamidomonas pulvisculus (Ehrenberg), and some other green and red animalcule belonging to a still lower grade in creation. I myself took an opportunity of verifying this remarkable fact, upon finding, in a trough of water in my garden, the fluid coloured green by the presence of various species of infusoria. I filtered it through a very fine sieve, in order to separate all confervse or vegetable matters, and then exposed it to the light of the sun in an inverted beaker glass completely full, the aperture of which was confined by water. After the lapse of a fortnight, more than thirty cubic inches of gas had collected in the glass, which proved to be so rich in oxygen, that a glowing splinter at once burst into flame in it. Without venturing to draw any inference from these data, with respect to the mode of nutrition of these creatures, it is certain that the water in which infusoria exist, under the influence of the solar light, contains a source of pure vital air it is certain that, from the moment these animals are perceived in the water, this water ceases to act injuriously upon the higher orders of plants and animals; for it is impossible to conceive that water should evolve pure oxygen, while it contains putrefying or decaying substances that is, matters which are capable of combining with oxygen. Now, if we suppose some animal matter in a state of putrefaction or decay added to water of this kind, this matter must, of course, be resolved into its ultimate products, in the presence of such a source of oxygen, in an infinitely shorter space of time than would be the case were these infusoria not present. ACTION" OF FUNGI AND INFUSORIA. 263 In the most extensively diffused animalcule, namely, the green, and red infusoria, we recognise a most admirable cause which removes from water all substances injurious to the life of the higher classes of animals, and creates in their place nutritive matters for the sustenance of plants, and the oxygen indispensable to the respiration of animals. The infusorial animalcule? cannot be the causes of putre- faction, of the production of poisonous matter deleterious to plants and animals, but an INFINITELY WISE INTENTION designs them to accelerate the transition of the elements of putrefying substances into their ultimate products. Among the fungi and agarics there are many species which develope themselves without light, and their growth and development are attended with all the circumstances characteristic of animal life. They contaminate the air and render it unfit for respiration, by absorbing oxygen and exhaling carbonic acid : in a chemical point of view, they are like animals without the power of motion. In contradistinction to this class of beings, which can scarcely be called plants, there exist living beings endowed with motion and provided with the characteristic organs of animals, which act in the light like green plants ; they, whilst multiplying in numbers and increasing in size, create sources of oxygen, and carry it with them wherever the access of oxygen in the form of air is impeded or altogether precluded. It is evident that infusorial animalculse can make their appearance, develope, and multiply, only in those places where they find an abundance of the necessary nourishment in a form adapted to assimilation. Several species, and these very widely diffused infusoria, are distinguished from other species by possessing certain inorganic constituents, namely, silica, which forms the shells, or cuirasses, as they may be termed, ofNaviculce, JZxilaria, Jlacillaria, &c., and peroxide of iron, which is a constituent of many Gallionellce. The car- bonate of lime of the chalk animalculso is precisely similar to the shells of the common molluscous animals. Many persons have pleased themselves with ascribing the 264 LETTERS ON CHEMISTRY. enormous depositions of silica, of lime, and of peroxide of iron in the siliceous fossil strata, in emery, in tripoli, in chalk, and in bog ores, to the vital process of primeval infusoria ; as if the formation of these enormous geological strata could be effected solely by the vital principle ! But they have altogether overlooked the circumstance that chalk, silica, and peroxide of iron must first be present as the necessary con- ditions of the life of these creatures before they could be developed ; and that those constituents at the present moment are never absent from the sea, the lakes, the marshes, where the same forms of animalcules occur in a living state. The water in which these primeval infusoria lived con- tained the silica and the chalk in solution, and in a condition perfectly suitable for their deposition in the form of marble, quartz, and other similar mineral masses ; and this deposition would have taken place inevitably in the ordinary manner, if the water had not contained the putrefying and decaying remains of preceding races of animals, and in them the other conditions of the life of siliceous and calcareous infusoria. Without a combination of these circumstances the pre- sence of these substances constituting the conditions of their existence none of these species of animalculee would have propagated and increased to form these enormous masses. These infusorial animalcule can only be considered accidental media of the form which the minute particles of these depo- sitions exhibit accidental, inasmuch as even without these creatures, deposition of the silica, the lime, the peroxide of iron, would have taken place. Sea-water contains the lime of the coral animals, of the innumerable mollusks existing in this medium, in the same form and condition as it is con- tained in lakes and in marshes, in which the chalk animal- culse develope themselves, or those mollusks the shells of which constitute the muschelkalk formations. The adherents of the theory according to which putrefac- tion is caused by infusoria and fungi, regard a putrescent body as a nursery of infusoria or a plantation of fungi ; and where organic matters putrefy over large surfaces, the whole SCABIES. MUSCARDINE. 265 atmosphere must be filled with the germs of these organised beings. These germs, in so far as they develope themselves in the bodies of men and animals, are, according to these phi- losophers, the germs of disease, and the essence of contagions and miasms. The foundation of this parasitic theory may be reduced to two facts : one is the propagation of scabies ; the other, a disease which occurs in the silkworm, the muscardine. Scabies, or the itch, is an inflammation of the skin, caused by a mite (Acarus scabiei, Sarcoptes humanus,) which lives in the skin, or, more properly, in its pores. In order to the communication of the disease, a continued approach, espe- cially during the night, of the healthy to the infected person, is necessary, because the Acarus scabiei is a nocturnal animal of prey. That the insect is really the contagion of scabies, is proved by the following facts : inoculation with the matter of the pustules does not excite scabies ; neither does inocu- lation with the crusts of these pustules ; the itch can be cured by rubbing with brick-dust but it cannot be commu- nicated by male Acari, but only by the impregnated female insect. The disease spreads over the surface by propagation of the animal ; it is chronic, and does not heal spontaneously. (HENLE.) The contagion is, therefore, an animal with a masticatory apparatus, which lays eggs. It is a fixed contagion, because the animal cannot fly, and because its eggs cannot be earned through the air. The muscardine is a disease of the silkworm, caused by a fungus. The germs of this fungus, introduced into the body of the worm, grow from within at its expense. After the death of the animal, they penetrate the skin, and on the sur- face appears a grove of fungi, which gradually dry into a fine dust, which, on the slightest agitation, rises from the sub- stance on which it lies, and is diffused in the air. It is the type of volatile contagions. Good nourishment and perfect health increase the liability to infection in the individual worms to which these germs are conveyed. But it has been observed, that a number of insects develope 266 LETTERS ON" CHEMISTRY. and propagate themselves only in the body or under the skin of higher animals, the disease and death of which is often produced by them. If we call the Acarus scdbiei a contagion, then all diseases caused by animals or parasites in the same way are contagions, since the size of the parasite can make no difference in the explanation. There are parasitic plants, like the muscardine, found in diseased fishes, in infusoria, in hens' eggs, and it is therefore certain that these observations establish a class of facts very frequently met with in the animal and vegetable kingdoms ; namely, disease and death caused by parasites, which live exclusively at the expense of the bodies of other plants or animals ; and if it is right to call a fungus a contagion, it must be admitted, since the size cannot effect the nature of the phenomenon, that there are contagia six or eight inches long ; for the Spkceria, Roberti, which is developed in the body of the New Zealand caterpillar, attains that bulk. When, however, we know that scabies is propagated by an animal, and other diseases by fungi, no special theory is required to explain infection in such cases ; and it is obvious that all states belong to the same class, in which we can detect the same or similar causes of their propagation. But, if we inquire what are the results of investigation, or of the search after such causes in other contagious diseases, we find, that in the contagion of small-pox, of plague, of syphilis, of scarlet-fever, of measles, of typhus, of yellow fever, of hospital gangrene, and of hydrophobia, the most conscientious observation has not been able to discover animals or any kind of organised beings, to which the propagation of the diseases can be ascribed. There are, consequently, diseases caused by animals, by parasites, which grow in the body of other animals, and at the expense of their constituents. These cannot be con- founded with other diseases in which such causes are entirely absent, whatever be the external resemblance between them. It is possible that, in one contagious disease or another, 'fur- ther research may show that they belong to the class of dis- eases caused by parasites ; but so long as this is not proved, VITAL AND PHYSICAL FORCES. 267 they must, by the rules of scientific investigation, be excluded from that class. The scientific problem is, to discover the special causes of these other diseases. The question, if pro- perly put, will lead us to the path by following which the answer is to be obtained. The greatest difficulty in such investigations is, obviously, that, when we have reached a certain point, we can no longer distinguish the effects of the vital forces residing in a living being from those of physical forces. All attempts to define strictly the line which separates animals from plants, to discover certain or infallible marks of distinction between them, have hitherto been unsuccessful. What we perceive are transitions, but not boundaries. There are actions, caused by physical forces, which exhibit many of the pecu- liarities of vital actions. In an animal of a high class we observe, in the arrangement of its parts, and in the wonder- ful agencies derived from these, so great and marked a difference, when compared with the phenomena of inanimate nature, that many are led to ascribe them to peculiar causes, quite different from inorganic forces. The vital phenomena, and their unknown cause, long appeared to naturalists so predominant, that the co-operation of physical and chemical forces was forgotten ; their presence was contested and denied. In contrast to this, in the lowest orders of plants, chemical and physical agencies so preponderated, that special proofs of the existence of vital forces became necessary. There arc living beings which in their form resemble inorganic precipitates. It is a fact, that experienced observers have taken crystalline deposits for Algce or Fungi, and have thus described them. At the boundary line, the effects of chemical forces are no longer distinguishable from those of the vital force. It is truly marvellous that the power active in animal organisms, the vital force, should be able to form, out of only four elements, a number of compounds, infinite even in the mathematical sense of the term ; that by it carbon, oxygen, hydrogen, and nitrogen, should be formed into substances possessing all the properties of metallic oxides, or 268 LETTERS ON CHEMISTRY. of inorganic acids and salts ; that upon the verge of what is termed inorganic nature, a series of organic elements begins, and becomes so extensive as to surpass the limits of our conception. We see the whole of inorganic nature, all the numerous combinations of the metals, reproduced in organic nature : with carbon and nitrogen, with carbon, hydrogen, and oxygen, with nitrogen and hydrogen, are formed compound atoms, which, in then* properties, are perfectly analogous to chlorine, to oxygen, or to sulphur, or to a metallic body not in a few isolated points of resem- blance, but in all their properties. It is scarcely possible to imagine anything more wonderful than that carbon and nitrogen should form a gaseous compound (cyanogen), in which metals burn with the evolution of light and heat, as in oxygen gas ; a compound substance which, in its pro- perties and deportment, is a simple substance an element, the smallest particles of which possess the same form as those of chlorine, bromine, and iodine, since it replaces them in their combinations without any alteration in the crystal- line form of the compound. It is in this, and in no other shape, that the living organism creates elements, metals metalloids, groups of atoms so arranged that the forces, active within them, acquire the power to manifest themselves in far more manifold and diverse directions than is the case with inorganic atoms. But there is no power in nature to produce substances out of itself, or out of nothing, none capable of annihilating those causes which impart to matter its properties ; iron never ceases to be iron, carbon never ceases to be carbon, nor hydrogen to be hydrogen. No iron, no sulphur, no phosphorus, can be created in the living organism. The opinions we have adverted to will be looked upon half a century hence with the same smile of com- passion which w r e bestow upon the dreams and fancies of alchemy. It belongs to human nature to form such notions, to create such hypotheses, wherever the mind, as is the case in infancy, is too little developed to comprehend the truth. The acquisition of the most common necessaries of life is KNOWLEDGE ACQUIRED BY LABOUR ALONE. 269 ever the fruit alone of labour and of effort. It is the same with intellectual wealth the knowledge necessary to increase and perfect our mental and moral powers, to obtain an insight into and an apprehension of all truth. There is want only where no firm WILL exists where no adequate efforts are exerted. The necessary means and instruments exist abundantly everywhere. , 270 - LETTERS ON CHEMISTRY. LETTER XXII. Connection of the Sciences True Province of Physiology and Chemistry Chemical and Physiological notions of Blood, Urine, and Bile, differ The Vital Force is something more than the known Physical and Chemi- cal forces The Vital Force must co-operate with known forces Little is known of the nature of Physical and Chemical forces Examples Crystallisation of Glauber's Salts Engravings copied by chemical means Action of the blood corpuscules in respiration. THROUGH Nature herself, whose kingdom forms a united and compact whole, the natural sciences stand in a necessary mutual connection, so that no one of them can entirely dispense with all the others for its development. The extension of the indi- vidual branches of science by researches, has the inevitable result, that in a certain stage, or at a certain period, two of them, for example, come into contact at their boundaries. As a general rule, a new science arises on the debateable land between them, w r hich combines in itself the objects and the modes of viewing the phenomena of both. In order to this interpenetration, both must have reached a certain advanced stage ; the independence of the original territories must be secured, for till this be done, the energies of the philosopher will not be applied to the border province. In these days we look forward to such a fusion of physiology with chemistry, as to one of the most striking results of scientific . investigation. Physiology has attained a point at which it can no longer dispense with chemistry in striving after its object, namely, the study of the vital phenomena in their natural succession. Chemistry, the duty of which is to show in what degree the vital properties depend on chemical forces, has been prepared, and is now ready, to take up new departments of science, to be independently studied. The phenomena presented by animals during their life are among the most complicated natural appearances ; and PHYSIOLOGY AND CHEMISTRY. 271 the detection of their different causes, and the ascertaining the precise share of each in the result, is a task of peculiar difficulty. It is a rule in natural science to divide every difficulty, which is to be examined, into as many parts as possible, and to study each of these separately. According to this rule, all physiological phenomena may be divided into two classes, of which each, up to a certain point, may be studied quite independently of the other. Such a separation, it is obvious, is not found in Nature, where both classes of phenomena are mutually dependent, so that, indeed, they mutually deter- mine each other. The processes of impregnation, development, and growth in animals, the mutual relations of their organs, and the agencies peculiar to these, the laws of their motion, and of that of the fluids of the body, the anatomical and other peculiarities of nervous and of muscular fibres ; all these striking and interesting phenomena may be ascertained without regard to the nature of the substances which form the parts in which these properties reside. But physiology has to do with other phenomena, not less important. Digestion, sanguification, nutrition, respiration, and secretion depend on a change of form and quality in the substances introduced from without into the system, or on certain solid or liquid constituents of the organism ; and it is in the study of these processes, so far as they can be regarded apart from structure, that chemistry must come to the aid of physiology. It is evident that physiology has two foundations, and that by the fusion of physiological physics, the foundation of which is anatomy, with physiological chemistry, which rests on animal chemistry, a new science must arise, a true phy- siology, which will stand in the same relation to the physiology of the present day, as modern chemistry does to that of the eighteenth century. In order to form a just idea of the interpenetration of physiology and chemistry, we must call to mind similar occurrences in the history of science. Thus the character of modem chemistry has been essentially determined by the 272 LETTERS ON CHEMISTRY. circumstance that it has absorbed into itself entire branches of physics, which now no longer belong to that science. The density of bodies in the gaseous state, forty years ago, was regarded as a purely physical character ; but since we have learned that this property depends on the composition in a fixed relation, the study of this property belongs to chemistry. Similar relations have been discovered between the specific heat, the expansion by heat, the boiling point, and the crystalline form of bodies, on the one hand, and their composition on the other; and it is now chemistry which especially occupies itself with the exact determination of these properties. The doctrine of electricity, so far as it is the result of a change in form and quality, of a chemical change, has now almost entirely passed into the domain of chemistry. Exactly in the same way, the more accurate knowledge of vital phenomena will establish the conviction that a number of physiological properties depend on chemical composition ; and physiology, when it shall have taken up animal chemistry as a part of itself, will possess the means of investigating this relation of dependence ; it will then be enabled to find a juster expression for physiological phenomena. Men have often tried to explain vital phenomena exclu- sively on chemical principles, and to make physiology a part of chemistry. This was done centuries ago, at a time when the chemical changes in the body were better known than the organism itself. But when men had learned to know the admirable structure, the form and quality of the organs, and their combined action by a more exact study of anatomy, they imagined that they had found the key in certain principles of mechanics. All such attempts have entirely failed ; and their failure gave rise to physiology as an inde- pendent science. Mineralogy was in a similar relation to chemistry ; forty years ago, many considered it a part of chemistry, and compound minerals were classed with the salts. Mineralogy conquered her independence, not 'by rejecting the doctrines of chemistry, but by taking into her own domain the determination of the composition of PHYSIOLOGICAL AND CHEMICAL TERMS. 273 minerals. Since mineral analysis has become a part of mineralogy, it is from mineralogists that we have obtained, and daily obtain, the most valuable results in regard to the relation which exists between the chemical composition of minerals and their crystalline form and other physical properties. One difficulty in effecting a mutual understanding, which, however, may easily be removed, still exists in the circum- stance, that in physiology, the same word does not always imply the union of the same things or of the same com- pounds with the same properties j but that, in using such words, less attention is paid to the nature and quality of the substance than to the part ascribed to them in the vital process, or their occurrence in certain organs. In physiology, for example, the words urine and bile are used to designate fluids, which are found in the sacs of certain organs, the nature of which may vary in many ways, without their ceasing to be regarded as urine or bile. In like manner, the physiological idea of blood is not derived from certain properties, but is attached, without any regard to form and colour, to the nutritive property, or the nutritive function of the fluid, and is inseparable from that idea, to which all other properties are made subordinate. In chemistry, which studies the properties of bodies, the names of urine, bile, blood, milk, &c., are attached to the complex ideas of certain properties in each ; in such a manner, that the name must not be given to a substance, when the properties included in it are wanting ; and since all these fluids are mixtures of several less complex com- pounds, chemistry distinguishes those which are invariable or characteristic from such as vary and do not determine the leading properties. The notion of urine is, in chemistry, inseparable from the presence of certain compounds, urea and uric acid ; and, chemically, the name of urine cannot be given to a fluid, in which these are entirely absent. Blood and milk are mixtures, the ingredients of which are present, not in fixed invariable proportions, but in 274 LETTERS ON CHEMISTRY. variable quantities. The mixed quality of the blood is even visible to the naked eye. Under the microscope we see minute red discs, the blood globules, swimming in a colour- less or pale yellow fluid, the serum, or rather liquor sanguinis. Lymph contains two colourless bodies, one of which coagulates spontaneously, as fibrine, at ordinary tem- peratures ; the other is coagulated by heat, as albumen. Its turbid milky appearance is caused by suspended and visible drops of fat oil. When lymph is agitated with ether, it becomes clear, the fat being dissolved by the ether. The mixed nature of some other fluids, as of the bile, is not so easily demonstrated ; but still it may be easily done by the use of chemical means of separation, such as we know do not produce any real chemical change in the * substances to which they are applied. The bile of animals is golden yellow, green, or yellowish brown j when freshly taken from the gall-bladder, it con- tains, mixed with it, a gelatinous, swelled up, tasteless matter, insoluble in water, which is entirely separated by the addition of alcohol. The alcoholic solution has the colour of the bile ; and if filtered through charcoal powder, the colouring matter is retained, while all the other constituents are found in the colourless solution. Bile, then, is coloured as blood is ; with this difference, that its colouring matter is dissolved, not suspended, although it is not in chemical combination with any of the other organic constituents. Were it so combined, the char- coal which retains it would also retain some other substance ; but it contains none, save the colouring matter. When bile is shaken with ether, or when a sufficient quantity of ether is added to the colourless alcoholic solution, the mixture forms two strata ; one a heavy syrupy liquid, which subsides, the other a lighter, which swims above it. The latter contains the ether, in which is found a quantity of fat. This fat was a constituent of the bile, not however suspended in drops as in lymph, but dissolved. The bile of birds, mammalia, fishes, and amphibia, so far as yet examined, behaves as above described towards alcohol, CHEMICAL NOTIONS OF BILE. 275 charcoal, and ether. It is no single compound, but a mixture of several such compounds. Were it a single compound, no one of its properties could be removed without destroying all or the greater part of the rest. Now, from bile we can remove its viscidity, its colour, its soapy quality, without the slightest change in the other essential properties ; but from the matter which is left, the purified bile, we cannot remove any one of its properties without destroying it. It is, then, a compound, or rather two compounds, of soda with two acids (formed by the coupling of the nitro- genised bodies, glycocoll [sugar of gelatine], and taurine, with the non-nitrogenised cholalic acid), and distinguished by its very bitter taste, and by the property of assuming a purple red colour when acted on by sugar and concentrated sulphuric acid.* The observation, that almost all parts of the animal body, the substance of the nerves and brain, and the fseces, con- tain the same kind of fat as the bile ; that the serum of coagulated blood has a colour very similar to that of bile ; that the mucus which forms on the surface of the intestinal canal is not distinguishable from the mucus of the gall- bladder : all this shows that fat, colouring matter, and mucus are not to be considered as essential or peculiar to the bile ; whereas the bitter substance, insoluble in ether, soluble in water and alcohol, is found in the healthy state only in the bile, and in no other part of the body. It is, therefore, regarded by the chemist as that which gives to the bile its character, so that, in a chemical sense, bile means only this one constituent. For the same reason, uric acid, urea, and allantoine, which are allied compounds, inasmuch as uric acid may be con- verted into urea and allantoine, are regarded as the characteristic constituents of the urine of all animals, because every urine contains two to one of them. Hippuric and benzoic acids, which are constituents of human urine, as well * It is remarkable that the bile of the swine contains a peculiar organic acid, analogous to, but distinct from, the acids of all other kinds of bile yet examined. T 2 276 LETTERS ON CHEMISTRY. as of that of the horse and cow ; and kreatine and kreatinine in human urine, are variable, not essential constituents, because they do not occur in the urine of birds and serpents, or at least have not been detected therein. It is well known that fresh-drawn blood, if left to itself, in a very short time coagulates to a gelatinous mass, and that this coagulation depends on a separation of the fibrine of the blood from the fluid (the serum) in the form of a jelly, or rather a network of infinitely fine colourless translucent fibres, which inclose the red globules, and thus form the clot. If the blood, before coagulation, be whipped or beaten with a rod or bundle of twigs, no clot is formed, because the fibrine is prevented from forming a network ; the fibres adhere into coarser elastic white masses, which, when washed with pure water, lose all red colour, and become perfectly white. This fibrine, if laid in water, to every ounce of which a drop of muriatic acid has been added, swells up to a stiff jelly, with- out dissolving ;* when the quantity of water is not too large, it is absorbed by the swollen fibrine as by a sponge ; and if concentrated muriatic acid be added to the mass, the fibrine shrinks to its original bulk. If again laid in water, it again swells up, and shrinks again on the addition of acid. After the fibrine has been thus treated alternately for ten times, it leaves, when dried and incinerated, 2 per cent, of ash, con- taining peroxide of iron, lime, and phosphoric acid. It is perfectly obvious that these substances were not merely mixed with the fibrine ; for they are retained by it with a force much greater than the strong affinity of muriatic acid for phosphate of lime and oxide of iron. These inorganic substances are, therefore, considered as essential and necessary constituents of the fibrine of blood. This want of mutual understanding in the terms used is not the only obstacle to the vigorous co-operation of che- mistry and physiology. A still greater difficulty lies in the * In these properties the fibrine of blood is very different from that of muscle, a chief constituent of the animal body ; which, under the same circumstances, dissolves into a clear liquid, only troubled by drops of fat suspended in it. FORCES IN OPERATION IN THE BODY. 277 difference of their methods of research. In the investigations of chemistry and physics, it is a principle, that a composite phenomenon must, above all things, be reduced, by observa- tion, to more simple facts. We then begin with the simple, and pass on to the study of the complex. The first questions refer to the proximate, not to the ultimate causes, and we proceed from the known to the unknown. In physiology and pathology, men long tried to investigate the most com- plex phenomena before they were acquainted with the simplest. They attempted to explain fever before they knew anything of respiration ; they explained the development of heat in the body, without taking into account the influence of the atmosphere j and the function of bile in digestion was explained before the composition of the bile was known. Hence the perpetual strife concerning the causes of life, which in itself is so little edifying, so purposeless, so profit- less, because the proximate causes of the simplest vital phenomena are hardly known to us. It is certain that a number of effects, observed in the living body, are determined by chemico-physical causes, but it is going much too far to conclude from this that all the forces which act in the organism are identified with those which govern dead matter. It is easy to show that those who adopt such an opinion have lost sight of the first and simplest rule of the physico-chemical method of inquiry, which directs us to prove that an effect which we ascribe to a cause really is due to that cause, and to no other. If heat, electricity, magnetism, and chemical attraction, are to be viewed as the causes of vital phenomena, we must first of all prove that those parts of the animal body, in which forces act, exhibit phenomena similar to those observed in inorganic bodies, when subjected to the action of the same .forces. We must show how the physical forces, above named, act together to produce the admirable harmony of arrangements presented by organised beings from their first development to the period at which their elements are again restored to the domain of inorganic nature. For if we suppose that the forces of inorganic nature are identical with 278 LETTERS ON CHEMISTRY. those of organic nature, we necessarily assume that all natural forces are known to us ; that their effects are ascer- tained ; and that we are able to deduce the causes from the effects, and to explain the share which belongs to each in the arrangements which constitute life. It suffices to cast a glance at the writings of the authors who defend this view, in order to perceive how far we still are from any such conclusion. This opinion generally pro- ceeds from very able and profound philosophers, who have attended exclusively to the phenomena of motion in the animal organism. Finding that these phenomena occur according to fixed mechanical laws, they are tempted to believe that they are determined by the same laws as the similar phenomena observed out of the body. But no one has hitherto ventured to point out the relations of these effects to heat, electricity, magnetic force, &c., or to show the degree in which they are dependent on these forces. All that we know of the matter is, that the inorganic forces have a certain share in these effects. On the other hand, it is quite impossible to partake the opinions of those who believe that they can explain the mysterious phenomena of life by the assumption of one or more vital forces. These persons take a phenomenon, with- out inquiring whether it be simple or complex. They ask, whether it can be explained by chemical affinity, or by the electric or magnetic force ; and since, at present, it is im- possible to answer this question in the affirmative, that is, as a matter of undoubted proof, they conclude that the phenomenon is determined by none of these forces, but by very peculiar forces belonging to living beings. But, in the search after the causes of phenomena, the method of exclusion is only permitted in those cases in which we are certain that the total number of causes to which the effect can by possibility be referred, is positively known and fixed ; and then only on condition of proving that the effects belong to one alone of all these causes. The physical forces, so far as concerns their nature and essence, are very little known ; and no one can maintain that NATURE OF PHYSICAL FORCES LITTLE KNOWN. 270 any one of them has no action in a given case, that it has no share in any given vital phenomenon. We have detected the most wonderful connections between the electric force and chemical attraction, but we are still far removed from knowing with certainty the real nature of these relations. Cohesion, or the cause of the grouping of homogeneous or like atoms into a mass, is known to us in its essence least of all ; and its relations to chemical attraction, to that which groups dissimilar atoms, are yet more obscure than those of the latter to the electric forces. Affinity, or chemical attraction, is to us, at this moment, the cause to which we ascribe, immediately, the combination of unlike atoms ; but the mutual attraction of the same bodies is not invariable, it does not always remain the same, and it is impossible for us to consider the force by itself, precisely because it never acts alone, and because, in order rightly to appreciate one of its effects, we are compelled to attend to those circumstances, temperature, cohesion, elec- trical state, &c., in which bodies are found, when we cause them to act on each other. We have recently become acquainted with a large number of phenomena, of which we hardly know which of all the known forces or causes have a share in producing them. In former ages, men would have hastened to deduce from this the existence of peculiar forces till then unknown. This we no longer do, because we are conscious of our ignorance in reference to the peculiarities of the known forces, especially of the so-called molecular forces, cohesion and affinity. If we place in a common champagne glass a solution, saturated at a high temperature, of Glauber's salt in water (two parts of the salt to one of water), and allow it to cool, the salt crystallises, and the liquid congeals to a thick mass of crystals, like ice. If the same glass be half filled with the hot solution, its mouth covered with a plate of glass, a watch- glass, or a card, and then allowed to cool, the liquid, after ten hours, or more, deposits no crystals, not even when the covering is removed. If we now immerse in it a common glass rod, the most beautiful needles and plates of Glauber's 280 LETTERS ON CHEMISTRY. salt, are formed from the surface of the rod, and in a few- seconds the congelation is complete. The liquid is in a glass vessel, but, although in contact with glass, does not crystal- lise ; another portion of glass, that had not cooled with it, instantly causes crystallisation. This appearance is suffi- ciently remarkable ; but still more striking is the fact, that if we heat one end of the same glass-rod for a few minutes in the flame of a spirit-lamp, and then allow it to cool, the rod, at that end, is quite without action on the crystallisation of the salt. It may be immersed in the liquid, and moved about in it, without causing the slightest change. But if we turn the rod round, and touch the liquid with the other end, which has not been heated, crystallisation at once ensues. To a superficial observation, the rod seems as if it now had poles, like a bar-magnet. At one end it retains a property, which it has lost, by the action of heat, at the other. If left exposed to free air, it gradually recovers the lost power ; but if enclosed in a shut vessel, it continues inactive on the solution for ten or fourteen days. Even after being dipped in water, and allowed to dry in the air, it has not recovered its lost efficacy. We have a sufficient explanation of the effect of motion on crystallisation ; but the action of heat on the property possessed by the glass-rod, of causing crystallisation, is, up to this time, utterly unexplained and obscure. If we place a copper-plate engraving on the top of a shallow open pasteboard box, on the bottom of which lies a little iodine, and thus expose it- for a few minutes to the vapours of iodine, such as rise at ordinary temperatures, and if we then press it firmly on a sheet of paper, which, like machine-made paper, has been sized with starch jelly, and is moistened with very diluted sulphuric acid, we obtain, on this paper, a most exact impression of the engraving in the most beautiful azure blue. If this blue impression be laid on a polished copper-plate, the blue lines gradually disap- pear, and the image now appears in perfect distinctness on the copper. A copper-plate, a drawing, even an oil-painting, when exposed for a short time to the iodine vapours, are ENGRAVINGS COPIED BY CHEMISTRY. 281 reproduced on a plate of silver, and when this plate is now exposed, as in the daguerreotype, to the vapour of mercury, and treated in the usual way, a beautiful daguerreotype picture is obtained, but without the aid of light. It is here quite obvious, that the dark parts of the copper-plate, or of the drawing, have attracted and condensed the vapour of iodine in a much higher degree than the white paper. A moist surface, containing starch jelly, attracts the iodine from the dark parts ; on the paper appears the blue iodide of starch, as a blue copy of the engraving. A plate of copper, again, attracts the iodine from the blue compound, and on the copper appears a copy in iodide of copper. It is evident that the white paper, the black colour or ink, the star*ch and the copper, have very unequal attractions for the iodine ; and that the cause of the condensation of the iodine is identical with that which effects the condensation of gases in general on the surface of solid bodies. The ink of the engraving attracts the iodine, but no true chemical com- pound has been formed; for the properties of the black colour remain unchanged, and the iodine has only had its volatility destroyed or diminished ; it acts on starch like free iodine. By these phenomena, we are involuntarily reminded of one of the most remarkable occurrences in the animal body, namely, the part played in the respiratory process by the solid parts or globules of the blood. The blood owes its colour to these globules or corpuscles ; and we see that these pass in the lungs from dark red to scarlet, while this change of colour is accompanied by an absorption of oxygen. The physiological phenomena, as well as the behaviour of the liquor sanguinis when separated from the globules, in contact with air and oxygen, teach us, that a great part of the oxygen which enters the blood is taken up by the blood corpuscles, which behave towards the gas as rough or coloured substances do towards the vapour or gas of iodine. The oxygen forms with them a compound of a peculiar kind ; for it retains, when absorbed or condensed, its chemical character, and its power of combining, in the 282 LETTERS ON CHEMISTRY. course of the circulation, with other bodies for which it has an attraction. We suppose that the attraction of the black ink of an engraving for iodine, and, as Niepce has shown, also for chlorine, and a number of other bodies in the form of gas or vapour, as well as that of the blood corpuscle for oxygen gas, is an effect of chemical attraction or affinity ; but our notions of the essence of this force are as yet so limited, that we have not even a name for this kind of combination. There are, as we see, phenomena enough which cannot be explained after the pattern of the usual notions, such as we have been taught ; there are signs and proofs that we are still very far from being acquainted with the laws even of known forces. We can resolve with a given quantity of sulphuric acid, unlimited quantities of alcohol into ether and water ; we can, by the help of the same acid, convert a quantity of starch into grape sugar, without the acid being neutralised in either case. These effects are quite distinct from the effects produced when sulphuric acid acts on metals or on metallic oxides ; but it is quite absurd to ascribe them to a peculiar cause, altogether different from chemical affinity. That which we commonly call a chemical action is a manifestation of chemical force, and is nothing more than a fact which proves that in a given case chemical attraction is more powerful than all the resistances which oppose its manifestations. But chemical combination is only one effect, and certainly it is not the only effect of chemical affinity. This imperfect state of our knowledge of the essence and of the effects of natural forces, explains how it comes to pass that at this moment we are unable by the method of exclusion or elimination, to solve the question of the exist- ence of a peculiar force or influence, acting in the living organism. ORGANIC AND INORGANIC FORCES. 283 LETTER XXIII. In inorganic nature, Mechanical and Chemical Forces predominate The properties of organic substances are due to the order of arrangement of their elements In organised beings a peculiar Force is in operation A Vital Force is denied by those only whose knowledge of Physical Forces is defective The law of Progressive Development has no found- ation in nature Views of Bischoff Chemical Forces may form an organic but not an organised body ; the Vital Force alone controlling the Chemical Forces gives rise to the latter Spontaneous generation has no existence in nature Views of the physiological materialists con- tested A Vital Force recognised. THE life of plants is dependent on the food obtained from the air, from water, and the soil. The elements of their living structures are derived from the inorganic substances, carbonic acid, water, ammonia, sulphuric, phosphoric, and silicic acids, and from alkalies, alkaline earths, and iron. But the processes which take place in the inorganic world are quite opposite to those which occur in plants. In inorganic nature predominate mechanical and chemical forces. The weathering of stones, the disintegration of lofty rocks, depend on changes of temperature, on the influence of water and air ; and organised beings, when life is extinct, are again resolved, by the action of oxygen, into the original compounds from which their bodies were formed. In the living organic frame of plants, however, air, water, oxygen, and carbonic acid, lose their chemical character, and exert no influence either through affinity or by their presence in preponderating quantities. Removed from the sphere of the vital force, oxygen exerts its powerful attraction for the combustible elements carbon and hydrogen ; but when subjected to this influence in the interior of plants, the hydrogen of water and the carbon of carbonic are separated from oxygen, and the latter is again 284 LETTERS ON CHEMISTKY. restored to the air. The vital process in plants thus exhibits itself as a process of reduction the opposite of the process of oxidation which takes place in inorganic nature. The greater number of the vital products of plants con- tain oxygen in combination with two to four combustible elements. From these few elements are formed an infinite number of organic compounds, exhibiting the most marked difference in their properties. If we compare cotton fibres, milk-sugar, the acid of sour-kraut, we are at once struck with their difference. But chemical analysis teaches us that these three substances contain carbon, hydrogen, and oxygen, exactly in the same proportions. Cane sugar and gum are also composed of the very same constituents. A hen's egg, as we know, becomes hard in boiling water, without being in the slightest degree altered in its composition. The elements composing it have only changed their arrangement, and with this alteration of position we find corresponding change of properties. The difference in properties of gum and cane sugar, of the acid of sour-kraut, and of cotton fibres, is, in like manner, due to a difference in the grouping of those elements, which are contained by them in equal proportions. Strychnine contains carbon, nitrogen, and the elements of water, and is a fearful poison ; whilst the same elements present in quinine form a valuable medicine. In caffeine, again, we see the same elements, and daily partake of this substance in tea and coffee without experiencing any poisonous or medicinal effect. All materials from which blood is formed contain nitrogen, carbon, and the elements of water. The poisonous, medicinal, or nutritive properties of strychnine, quinine, and azotised articles of food, cannot therefore be ascribed to their carbon, nitrogen, or the elements of water, but must be due to the manner in which the elements are arranged in each substance. By one mode of grouping they check the vital process ; by another they promote, and by a third they sustain it. By ultimate chemical analysis we do not obtain the slightest clue to the real properties of organic compounds. Hence, in investigating the different vital products of plants, ELEMENTS COMPOSING A HOUSE. 285 chemists have latterly directed all their efforts to ascertain the order of grouping of their elements, on which they see that their properties are dependent. Were a chemist to submit a house to analysis, he would state its composition scientifically to consist of silicium, oxygen, aluminium, and calcium ; and of a certain quantity of iron, lead, copper, carbon, and the elements of water. But this would not convey the most distant idea of the construc- tion of a house. The calcium, carbon, and oxygen of the mortar ; the silicium, aluminium, and oxygen of the bricks ; the carbon, water, and oxygen of the wood, do not play the part of elements in the structure, but they are present in the form of mortar and stone in the walls, as glass in the windows, as wood in the tables and seats. It . is only when combined in the form of wood, stone, glass, &c., that these elements contribute to the construction of the house. If any one assured us that the palace of the king, with its entire internal arrangement of statues, and pictures, started into existence by an accidental effort of a natural force, which caused the elements to group themselves into the form of a house, because the mortar of the building is a chemical compound of carbonic acid and lime, which any novice in chemistry can prepare, because the stones and glass consist of silicium, aluminium, calcium, potassium, and oxygen, united by chemical affinity, and indebted to the force of cohesion for their solidity, because therefore chemical and physical forces play a part in the construction of the house, we should meet such an assertion with a smile of contempt, for we know how a house is made. Its outer form, its inner arrangement of rooms, &c., proceed from the architect. He constructs the actual house after the plan of an ideal house which exists in his own mind. He realises the ideal creation of his own mind in the building by forces which are produced in the organism of man, and which impress into the service of this ideal creation the chemical and physical forces from which the building material has received its properties. Everywhere the existence of a 286 LETTERS ON CHEMISTRY. house presupposes the ideal perceptions of the house in the mind of some one who is its builder or cause, which sets other forces in action in certain directions or in a certain form, in order to gain the object in view. In the structure and development of the lowest, as well as of the highest orders of plants, their materials are arranged with a beauty and regularity far surpassing the utmost efforts of the architect in the erection of his house. In each species of plants the same plan is repeated ; and this from its unchangeableness, comes to be regarded as the natural law of that species. We see it stand before us at last perfect and complete in all its parts, and ready to be reproduced after a certain time in the seeds. Our senses can only see the hand of the architect in his work. We can recognise an idea, a plan in the development of these forms according to fixed laws, but we cannot see the forces which have controlled the resisting materials, and forced them into the prescribed arrangement. Our reason, however, tells us that the idea must have had an author, and that there exists in the living body a cause which controls the chemical and physical forces of matter, and determines it to assume forms never observed out of the living organism. The figures of all inorganic bodies are bounded by flat faces and straight lines, and of organic bodies by curved faces and lines. In organic bodies there must therefore be some cause in operation which converts the straight into the curved line. A defective knowledge of the forces operating in inorganic nature is the reason of many denying the existence of a parti- cular active force in organised beings, and of their ascribing to inorganic forces effects which are quite contrary to their nature, and opposed to their laws. They do not even know that the existence of a chemical compound presupposes the existence not of one but of three causes. For the arrangement of the particles in the crystalline form, and the properties which are connected with this arrangement, are the result of the force of cohesion, acting in concert with heat and chemical affinity. In living bodies a fourth cause comes into play, controlling the THE DEVELOPMENT THEORY. 287 force of cohesion, and grouping the elements into new forms with new properties, such as are never observed out of the living organism. If it is a fact that in inorganic nature there exists a force, which we call the force of cohesion, determining the form of chemical compounds ; it must be equally true that in living bodies there is a force in operation opposed to cohesion, and which is able to arrest the action of oxygen, and to reverse the most powerful chemical attraction. The opponents of this opinion are easily seen to be total strangers to all investigations connected with chemical and physical forces. No well-informed natural philosopher or chemist has ever ranged himself on their side. If we refer the question to our great physiologists, to whom we are indebted for the discovery of those facts on which the opponents of a vital force found their assertions, these masters of science will reply, that such assertions are utterly without foundation. They are the speculations of amateurs, who assume the right, after a very slight acquaintance with the investigation of natural phenomena, of expounding to an ignorant and credulous public the wonders of creation and of life, and of setting forth to them what progress has been attained in the highest departments of science. And such ignorant and presumptuous dreamers are listened to more readily than the most philosophic inquirer. These amateurs maintain that in the course of an infinite series of years, which they dispose of with a dash of their pen, the vast variety presented in the organic creation, was gra- dually developed from the lowest form of organisation, a simple cell. Plants and animals formed an unbroken chain, and transitions from the one to the other could not be disputed. If in many cases such transitions cannot be traced, the explanation is partly found in the immense periods, reaching beyond the history of man, which intervene between them; but chiefly in the later transition stages becoming so gradual as to escape the notice of the most acute observer. The true spirit of a superficial inquirer is evident in this statement. The hypothesis is not based on facts, and is therefore incapable of proof. Neither can it be refuted, for 288 LETTERS ON CHEMISTRY. the authors protect themselves with the assertion that the experience of man is insufficient to test its truth. They cannot, however, escape from the difficulty which still remains to be explained, viz., whence is the origin of the first organic cell. This one cell, they tell us, was called into existence by the fiat of the Creator, and all others were developed from it. This school of physiologists thus presume that it was more conformable to the purposes of the Creator to bestow vitality on this one cell rather than on many, and having created it, to leave to time and chance the full unfolding and development of organic nature from this one cell. Let us hear what is said by Bischoff, a great authority on embryology (in his memoir read at Munich in Spring, 1858), about this chain formed by organic nature. " In the middle of the last century, naturalists first became more fully acquainted with the Ourang-outang of Borneo and Sumatra, and with the Chimpanzee of the coast of Guinea, from dead specimens, and partly from the living- animals which were brought to Europe. The great natu- ralists of that period, Linnaeus, Buffon, Camper, &c., after examination of these creatures, felt quite at a loss for distinctive characters, drawn from the bodily organs, to distinguish man from the lower animals. The correspond- ence and similarity of these apes to man seemed so great, that some thought they saw no difference whatever between them, and others believed the differences to be very sub- ordinate, and not existing in the relations of the bodily organs. The most exact scientific inquiries seemed to establish the connection between man and the lower animals by an almost imperceptible transition. At that period the animal creation was regarded as forming an unbroken chain, the links of which were closely connected, and consisted of forms gradually developed from the lowest to the highest, and passing naturally by the most imperceptible degrees to man himself, the last link of the chain. The minute in- vestigation of the development of each individual animal appeared also to support this proposition. It was received as an established fact, that the higher class of animals, and BISCHOFPS VIEWS. 289 even man, passed in the embryo state, and during their development, through all the stages of the lower forms of animals; that man, for example, before finally arriving at his own peculiar form, first passed, in the embryo state, through the different stages of infusorium, worm or insect, fish, amphibium, bird, and higher mammal. It was held as absurd and insufferable pride to place man higher than the other animals, and prejudice alone was supposed to lead us to look for distinctions between them, in order to support such pretensions. " Such views could not, and never can, long maintain their ground. The study of nature, the foundation on which they rest, necessarily leads to their overthrow, and to their restriction within the limits in which they are true. The well known axiom receives here its application ; viz., that science, when pursued with imperfect knowledge, or on a false system, leads only to error and disappointment ; but it is rewarded with the discovery of truth, when it rests on correct and just principles. " The more closely the structure of animals, and particularly of these rare apes, was studied, it became only more evident that, notwithstanding the great similarity between them and man, there nevertheless existed as great corporeal differences as served to distinguish genera and species in other departments of nature. The universally received and favourite doctrine of progressive development, resolved itself, on closer inspec- tion, into single members and types, which indeed exhibited among themselves undoubted evidence of this progress in organisation, but which, so far from forming by gradual transi- tions an immediate and connected series, presented greater intervals and differences than would be sufficient to constitute a distinct line of separation between man and animals. " We learn further, by a more exact insight into the wonder- ful process of the development of each individual species, that the embryo does not pass through the different stages of the lower forms of animals ; that the human embryo never resembles an infusorium, worm, insect, fish, or amphibium; but that all vertebrate animals obey a highly wonderful law 290 LETTERS ON CHEMISTRY. of evolution common to all. In the first stages of their development the embiyos undoubtedly resemble each other, for in the commencement they consist of the same number of similar parts, such as brain, spinal column, heart, intes- tinal canal, &c. The characteristic differences which after- wards arise, result not alone from higher development, but as frequently from arrestment, or retrogression, at a certain stage of evolution." Exact scientific investigation then ignores the existence of a connected chain of organic life. What then becomes of the first created cell 1 Superficial inquirers reply, that organic nature is formed of carbon, water, nitrogen, oxygen, and sulphur ; that in the constant interchange taking place among these elements, it may possibly so have happened that by their own inherent power they united and formed the cell, and so the organic structure. The chemist can in his laboratory prepare a number of substances, formerly obtained only from living plants and animals. He can make sugar from wood, he can prepare urea and the taurine of bile, why then may carbon, water, and the other elements, not unite of their own accord and produce a germ ? But what these superficial observers designate organic sub- stances are only chemical compounds containing organic elements. The taurine extracted from bile cannot be distin- guished from that made in the laboratory ; they are both formed by a chemical, but not by an organic force. It is self-evident, that chemical forces are in operation in the living body. Chemistry now proves what she asserted thirty years ago without the ability to offer proof. Under the influence of a cause which is not chemical, we see chemical forces acting in the living organism. As the intelligent will of the chemist forces the elements external to the body to combine into the products urea, taurine, &c., so within the body these same elements unite to form these same products, not by any inherent power of their own, but by the controll- ing action of this vital cause. It will be within the chemist's power to form quinine, caffeine, the colouring matter of plants, CHEMISTKY CANNOT FORM AN ORGANIC GERM. 291 and all other compounds which possess chemical but not vital properties, the smallest particles of which in arranging themselves into a crystalline form are not under the influ- ence of an organic force : but he will never succeed in con- structing in the laboratory a cell, a muscular fibre, a nerve, or in short any one single portion of the organic frame pos- sessed of vital properties. Whoever has seen carbonate of ammonia, carbonate and phosphate of lime, an iron- ore, an alkaline mineral, will at once pronounce, that it is impossible by means of heat, electricity, or any other natural force, to form from these substances an organic germ, capable of fur- ther development and propagation. Inorganic forces produce only inorganic substances ; but organic bodies, with their peculiar forms so different from crystals, and endowed with vital properties, owe their origin to a higher force, acting in the living body, and which presses into its service the inorganic forces. A hundred years ago, it was believed that fishes and frogs were spontaneously produced in bogs, and that plants and all kinds of insects were formed in fermenting and putrifying mixtures, and in moist saw-dust. Had this been true, then doubtless might a man under similar circumstances have been also spontaneously produced. Exact inquiry, however, proved that all these opinions regarded as facts were based on false and frivolous observations. In every well investigated case, germs and seeds of plants, and eggs of animals were discovered which were developed in mould ; but an egg, a seed, has its origin in a living organism. Many philosophers have asserted, that life, like matter, has existed from all eternity. Exact inquiry has, however, proved, that at a certain period the earth possessed a temperature which was incompatible with organic life ; for coagulation of the blood takes place at 78 C. (172 a Fahr.). Organic life must therefore have had a beginning. These are important facts, and had they been the only acquisitions of this century, philosophy would still have been under an obligation to the natural sciences. u 2 292 LETTERS ON CHEMISTRY. These same superficial observers and novices in natural inquiries, who know nothing of the nature of fever, inflam- mation, or catarrh, or of the formation of the blood, or of the use of the bile, would lead an ignorant and credulous public to believe, that they are quite qualified to give expla- nations on the origin of thought, and on the nature and essence of the human mind. In their authoritative style, they pronounce intellectual man to be the result of the operation of his senses. Thoughts owe their origin to an interchange of matter in the brain, which thus acts the same part as the liver in the production of bile. As the bile perishes with the liver, so also does mind with the brain. When we divest the views of these men of their false pretensions concealed under pompous language, and expose them as they in reality appear to reflecting philo- sophic minds, we find that they shrink to the mere assertions, that legs are destined for walking and the brain for thought ; that the art of thinking must be learned, just as the art of walking by a child ; that without legs there can be no loco- motion, any more than there can be thinking without a brain ; that an accident to the organs of locomotion impedes our movements, just as injury to the brain disturbs the process of thinking. Flesh and bones, the component parts of the legs, cannot however put themselves in motion. They are but the instruments of a force, which is neither flesh nor bone, and which is the cause of their movement. The soft mass which we call brain, is but the instrument of the cause to which thought is due. The brain is the only internal organ, directly subject to the will of man. Neither the heart nor the stomach is under its immediate influence ; but every teacher is familiar with the wonderful effect of a box on the ear when applied at the proper moment in sharpening a boy's perception of a mathematical problem. The eye and the ear are the mere instruments for perceiving the undula- tions of light and sound. The superficial observers, of whom we have been speaking, assert that thoughts are the result of the interchange of elements in the brain, just as bile is produced by this cause VIEVYS OF THE MATERIALISTS. 293 in the liver. Exact physiological inquiry has, however, up to the present moment, not been able to show any relation between the bile, the secretion, and the interchange of elements of the liver, the secreting organ. As far as chemistry has yet ascertained, there appears to exist no connection between the elements of the bile and those of the liver. When the chords of the harp, moved by the wind, give forth their tones, they are caused by a movement of the air, which the ear transmits to the brain ; but the ear does not hear, and the tones are not music. In like manner the brain, when its substance undergoes change, may produce thought, but it cannot of itself give rise to ideas ; neither can the ear hear music, nor the eye see the sun, nor the green trees, nor read the language of love addressed to it. Thoughts produced by the brain, by a change in its sub- stance, are like types for printing, which when set in motion do not produce a book. For thoughts which are to express ideas there is required something of a higher order, an intelligent will, which arranges them according to fixed laws. The nerves can feel no pain, no change of tem- perature, they cannot perceive the physical properties of matter. The intellectual being, man, is not produced by the simple operation of the senses, but the operations of the senses themselves are the results of an intelligent will in man. We know that change of substance produces power hi the steam-engine. Wood and coals, in burning, change their properties. In the galvanic battery, change of substance, by the solution of a metal in an acid, gives rise to an electric current ; and this to a magnet, which sets a machine in motion. Everything leads to the belief, that in the animal body also, the mechanical force, which determines the volun- tary and involuntary movements of the members, is in like manner connected with change of matter, particularly in the muscular system ; but we know as yet nothing of the relation in which these stand to each other as cause and effect. This much, however, we know, that this force is not 294 LETTERS ON CHEMISTRY. produced in the organism, as in the steani-engine ; nor can we apply to it the known laws of electricity. We know that change of substance is constantly taking place in all parts of the body ; that the exhaustion of mechanical force exerts an influence on all parts of the frame ; that the will of an individual, fatigued by running or by hard labour, loses its power of command over the brain, the instrument of thought. Changes of matter, in these different cases, with the attendant results, we know ; but change of matter in the brain giving rise to thought as its result, is utterly unknown to the philosophic investigators of nature. The extent of our knowledge on this point is limited to the truism, that a head without brains cannot think or perceive. We produce magnetism and heat by electricity, and electricity and heat by magnetism ; and each of these forces is convertible into an equivalent of mechanical force. Undoubtedly they all take part in all material changes and processes of the body ; but it is impossible to accept the conclusion, that forces which manifest themselves in attrac- tion or repulsion, in extension or contraction, can either alone or together produce self-consciousness. Were this possible, then, according to the doctrine of the indestruc- tibility of force, thoughts ought to lift weights, or be con- verted into magnetism, electricity, or heat. Were the mental manifestations consequences and not causes of material changes, then should consciousness and changes in matter stand to each other in the same relation. Scientific inquirers, who were truly anxious to become acquainted with the laws of organic life, but who perceived the predominance within their own bodies of physical and chemical forces, naturally turned to them their attention, as to forces already known. They at once withdrew from the consideration of other forces in order to test the extent to which chemistry and physics are applicable in the explanation of the phenomena of life. When these proved insufficient, a new and unknown principle was then called into play, limited and circumscribed in its extent. This method of A VITAL FORCE RECOGNISED. 295 exclusion was not known or understood by many ; hence they imagined that the supporters of the physical and chemical laws of life rejected the idea of the operation in the organism of any peculiar force different from these. To do justice to the materialists, we must take into con- sideration that their views are in reality but the consequence of an extreme reaction against the prevailing doctrines of a few years ago. The physiology of that period did not possess the firm foundation of exact inquiry, viz., experiment. All the processes of nutrition, respiration, and motion, were referred by it to a single imaginary cause, viz., the vital force. In the organic frame, physical and chemical forces had no part. The organism produced in its own peculiar way the iron and other materials which it required, just as it did heat. Exact inquiry has, however, proved that all material laws are actually in operation in the various organic processes, and the consequence has been, that the extreme reaction against the earlier views has led to the opinion, that no forces but those of chemistry and physics preside over the phenomena of life. Incapable as the natural philoso- phers of a former period were to prove the operation of a vital force in every process of the organism, the materialists of a later period are equally unable to show, that their inorganic forces take the place of the vital force, 'and even give rise to the manifestations of mind. The assertions of both parties are equally without foundation, and arise from the want of a true knowledge of the processes of the living body. Between these extremes lies the truth, which rises above all partial speculations, and recognises in the living frame, in addition to the physical and chemical forces, another cause which presides over, and determines the forms of organic structures. LETTERS ON CHEMISTRY. LETTER XXIV. Scientific study of obscure objects Example Origin of the belief in Spontaneous Combustion of the human body Alleged cases of it ill- observed The fact assumed on insufficient grounds In all the cases, a light or burning fuel has been in the room, and in no case has the com- bustion been witnessed Flesh is not combustible till dried, and then it is not combustible like wood Living flesh cannot burn, nor does steep- ing it in fat or spirits render it combustible All nitrogenous compounds are comparatively incombustible The Electrical theory is altogether- fanciful The supposed cases arose generally from intoxication ; the victim of drink falls on the fire or sets fire to the bed or furniture, and is suffocated, and his body partly consumed. THERE is scarcely a more striking instance of the differ- ence between the present and former modes of investigating and explaining natural phenomena than the so-called spon- taneous combustion of the human body, which was accepted as a fact in medicine, and was considered worthy of engaging the attention of even scientific medical men. More than a hundred and twenty years ago, in 1725, the remains of a woman, the wife of an inhabitant of Rheims, named Millet, were found burned in her kitchen, about eighteen inches from the open fireplace. Nothing was left of the body, except some parts of the head, of the legs, and of the vertebrae. Millet had a pretty servant girl, and the suspicion arose against him that he had murdered his wife. A criminal inquiry was instituted, but learned experts acknow- ledged spontaneous combustion, and Millet was pronounced innocent. This is the first, or one of the first, recorded cases of the so-called spontaneous combustion. It is easy to see that the idea of spontaneous combustion arose at a time when men entertained entirely false views on the subject of combustion, its essence, and its cause. What takes place in combustion, generally, has only been known for seventy SPONTANEOUS COMBUSTION". 297 years, that is, since the time of Lavoisier ; and the conditions which must be combined, in order that a body should con- tinue to burn, have only been known within the last forty years, or since the time of Davy. Since that first case, there have occurred, down to the present day, from forty-five to forty-eight cases, of which the \ great majority agree in the following points : 1. They took place iii winter. 2. The victims were spirit drinkers, in a state of intoxication. 3. They happened where the rooms are heated by fires in open fire-places, and by pans of glowing charcoal, in England, France, and Italy. In Germany and Russia, where rooms are heated by means of closed stoves, cases of death, ascribed to spontaneous combustion, are exceedingly rare. 4. It is admitted that no one has ever been present during the combustion. 5. None of the phy- sicians who collected the cases, and attempted to explain them, has ever observed the process, or ascertained what preceded the combustion. 6. It has also been invariably unascertained how much of combustible matter was on the spot. And, 7. It is also unknown how much time had elapsed from the commencement of the combustion to the moment when the consumed body was found. The descriptions of cases of death from spontaneous com- bustion, which belong to the last century, are not certified by highly cultivated physicians ; they commonly proceed from ignorant persons, unpractised in observation, and bear in themselves the stamp of untrustworthiness. In these accounts, it is usually stated that the body entirely disap- pears, down to a greasy stain on the floor and some remains of bones. Every one knows that this is impossible. The smallest bit of bone in the fire, becomes white, and loses somewhat of its bulk, but of its weight there remains from 60 to 64 per cent, of earthy matter, commonly retaining the form of the original bone. In a very few cases it is not known whether fire from without, a spark, a lighted candle, or a red-hot coal, may not have caused the combustion. The most learned and distinguished physicians, such as 298 LETTERS ON CHEMISTRY. Dupuytren, Breschet, and professors of medical jurisprudence, such as Devergie, consider all the cases in which it is assumed that the body alone, without an external cause, such as a candle, a red hot coal, or a spark, has begun to burn, and continued to burn, as incredible, unproved, and improbable. Dr. Franck (Encyclop. Worterbuch, Berlin, 1843), out of forty-five cases adduced by him, excepts three, in which he admits this to have taken place. A closer examination of the most important of these three cases will show what is to be thought of it. It is told by Battaglio, a surgeon in Ponte Bosio (a surgeon in Italy in J the year 1787 may be considered as equal to a bather or rubber). A priest, named Bertholi, goes to the market at Filetto, to transact business there, and lodges with his brother-in-law in that town. In his bed-room he has a sackcloth placed between his shirt and his shoulders, and when left alone, betakes himself to the reading of his prayer-book. A few minutes later, an unusual noise is heard in his room ; he is heard to scream, and the people of the house find him stretched on the floor, surrounded by a light flame, which, as they approach, recedes, and at last disappears. The skin (epidermis) of the right arm and of the surface from the shoulders down to the loins, was found detached from the flesh. The shoulders, protected by the sackcloth, were not injured ; the sackcloth itself showed no trace of fire ; on all the injured parts the shirt was consumed, and everywhere, where the dress was not burned, no injury was found below it. The drawers and legs were not affected by the burning. Dr. Marc (Diet, des Sciences Med. torn. vi. p. 85) attaches singular importance to this case, and declares that it sheds light generally on the cause of the phenomenon of sponta- neous combustion, which he thinks must be sought for in electricity. This case is one chief support of the opinion, that a spon- taneous combustion is possible, and there has been attached to it the idea of a very peculiar fire, which burns animal CASE OF SPONTANEOUS COMBUSTION. 299 matter, without kindling the surrounding objects. But neither Marc nor Franck, who separate this case from the others, mention what is stated by more conscientious and accurate observers, namely, that, before the combustion, a lamp filled with oil was in the room, which lamp, after the event, was found empty, and its wick burned to ashes. If we reflect, that the body was burned only where the shirt was consumed, that no marks of fire appeared on the other parts where this had not happened, and further, that the skin was not burned or charred, but only detached (it hung down in shreds) from the body, while the shirt was entirely burned and reduced to ashes, it is quite impossible to admit that the kindling and combustion of the shirt were caused by the skin, which yet did not itself burn ; and no other explanation remahis, but that the shirt had caught tire, and that the burns or wounds were the results of its very superficial combustion. The presence of the lamp, which, as the disappearance of the oil proves, had burned, removes every doubt as to the origin of the fire. The report of Battaglio exhibits a striking example of the peculiarities which have sometimes been noticed in cases of so-called spontaneous combustion, namely, that substances, naturally combustible, do not take fire from contact with the burning human body, which led to the belief in a peculiar kind of fire, different from ordinary fire. He relates, that the priest's skull-cap was entirely consumed, without singeing the hair in the slightest degree ; and he adds, that he certifies this fact as thoroughly true and established. If we assume that the priest had the skull-cap on -his head, which Battaglio obviously assumes (for had the cap been on a chair, and there burned, the fact of the hair not being singed would certainly have excited no wonder), then we must regard this as an accidental circumstance, from which 110 one will con- clude that it was a peculiar kind of fire which consumed the cap. Whatever may have been the state of health or disease of the priest, it is certain that the skull-cap did not share in this state of health ; it was not diseased, and had in itself no cause to break out in flames ; nor if it did so, was there 300 LETTERS ON CHEMISTRY. any reason why the flames should contain a fire different from all other kinds of fire, all of which burn hair. This one example may serve to show how untrustworthy are the three solitary cases, in which it is assumed that combustion occurred where no fire was in the neighbour- hood.* The admission of the spontaneous ignition of the body, and of its consequent combustion, contradicts so greatly the known laws of combustion generally, and the known com- position and quality of the body, that natural science has hitherto taken no notice of the statements made as to the facts nor of their explanation. With regard to the other forty-five or forty-eight cases of death, ascribed to spontaneous combustion, it is not sup- posed by the writers on the subject that the victims took fire of themselves, burst into flames, and were burned ; but these writers admit that an external cause, a source of fire, was present. They assume that the body was set on fire by external means, but that it then burned on, without external * The second example is one which a well-informed man can hardly venture to repeat ; for, in the person to whom it occurred, the fingers of the right hand burned, and kindled the trousers, as also, by contact, the fingers of the left hand. This fire continued to burn when the burning parts were immersed in sand, and could not be extinguished by water. The third case occurred to clergyman in America, who felt in the left leg a pricking pain, as if a hair had been torn out ; he then saw at the spot a small light flame, which, when covered with the hand, was extinguished, and left a mark or burn, three-quarters of an inch broad, and three inches long. Here, also, the clothes over the spot were burned through, but the skin was not burned ; there was not even a blister ; the skin was as if scaled off, very dry, and of a dark colour. (Overton, American Journal, Nov., 1835.) This kind of spontaneous combustion probably occurs very often to cigar smokers ; but, as told, it resembles a Yankee yai-n, a joke of Uncle Sam, or of David Crockett. On the case of the sempstress Heinz, aged 17, in Hamburgh, Devergie remarks (Diet, de Med. et de Chir., v. 375), "the process of healing of the burned parts destroys all the>upposi- tions we might make concerning spontaneous combustion." Dr. Franck says of the same case (Encycl. Wb'rterbuch, vol. xxxi. p. 528), that he agrees with Kiihn and Devergie, that Heinz, who was hysterical, had deceived the deceased Fricke, no one having seen the combustion. The latest case, related in the Journ. des Debats of Feb. 24, 1850, is one of those standard newspaper paragraphs which, as is well known, periodically make their appearance, like the great sea-serpent, which so many American travellers and trustworthy sailors and sea captains have seen and de- scribed. SPONTANEOUS COMBUSTION WITHOUT PROOF. 301 heat continuing to act on the body. They admit that the human body, in itself, is very difficult to burn, but that the flesh, skin, and other parts, in consequence of diseased condi- tions, caused by indulgence in ardent spirits and other causes, may become more combustible ; not combustible like a bit of wood, which, when kindled and laid on the ground, soon goes out, but like a bundle of straw or a tallow-candle, which, once ignited, continues to burn till nothing but ashes or charcoal is left. The fact that some one, a hundred and twenty-five years ago, expressed the opinion that human bodies can burn in the way just described, and that, since that time, the same opinion has been held by some concerning forty-eight similar cases, affords not the slightest proof of the truth of that opinion. There are historical proofs of an event : for example, that in this town, on a day and at an hour described, a person has been found dead, and burned. But there is no historical proof in favour of the opinion, that this person took fire spontaneously ; and, in like manner, there are no historical proofs of the truth of the opinion, that there exists a morbid state of the body, in consequence of which it acquires the combustibility of a bundle of straw. To admit, as true, such opinions, the grounds on which they rest must, before all things, be recognised as true and free from doubt, and the facts with which these grounds are connected must be most exactly ascertained. To demonstrate the truth of the first opinion, not only must we prove that it is possible for a piece of flesh to become thus combustible, but we must prove that such combustion, when it occurred, has proceeded from the flesh outwards. With regard to the second opinion, it must be shown that a morbid state, such as is assumed, actually exists ; and, further, that the persons who were burned were in that morbid condition. Nothing of all this has been done. Not one of those who are adherents of the theory of spontaneous combustion, or .302 LETTERS ON CHEMISTRY. who, as authors, have endeavoured to support it, has ever occupied himself with experiments to learn the behaviour of animal matters in the fire.* Not one of them has ever in his life observed a morbid state, by which the body is rendered easily or quickly combustible. Not one of them can tell the signs by which such a state may be recognised. The supporters of that theory say, that the possibility of spontaneously taking fire, and the fact of spontaneous com- bustion in living or dead human beings, is not refuted by all that modern science knows. It is not their business to explain how this combustion is effected ; they merely assert that it does take place. They say that circumstances and facts, quite unequivocal, in the recorded cases, speak in favour of this view. "How many phenomena," say they, " exist in nature, which science cannot yet explain ! And yet these phenomena do not, on that account, cease to be true. How many unknown forces may yet exist, of which modern Chemistry has not even a presentiment ! And is it fjust or fair, or even decent, to reject, off-hand, the testimony of so many men who have avowed their belief in spontaneous combustion, and to class them with liars or blockheads, simply because we do not agree with them 1 " All such remarks do not form sufficient grounds to justify an opinion; for every kind of assertion may be defended by similar statements, if it contradict common sense. They apply to all. These reasoners entirely forget, that nobody doubts the facts of the deaths by burning in these cases, any more than the existence of a number of unexplained phenomena is doubted. The fact stands sure ; but the explanation does not. What they assert, is not the fact ; this fact or occurrence is, and continues to be, true, even without their assertion of it. But not so, that the death occurred in the way imagined by them, and can only be explained in that way. It is a fallacy to say, that they do not try to explain the fact ; for they do actually try to * Julia-Fontenelle has arrived by his experiments at a totally dif- ferent opinion. SPONTANEOUS COMBUSTION WITHOUT PROOF. 303 explain it by asserting that the body has become combustible, and has been burnt, of itself, without external aid, and in virtue of a cause residing in itself. But to comprehend or admit this explanation, we must obviously ask for the proofs which support it ; and when it appears that there are no such proofs, or that those adduced are fallacious, that is, that they contradict known and established truths, we cannot admit, as true, their explanation of the fact of burning, namely, how and in what way a man takes fire spon- taneously. When a physician declares that a man has died by suffo- cation, or from an inflammation of the lungs, this presupposes that he is acquainted with the accident or the disease which preceded the death; or he must, after death, have recognised the signs of asphyxia, or on dissection have found those of inflammation. If he know nothing of all this, it is impossible, even for the ablest man, to form an opinion as to the cause of death. The opinion, that a man can burn of himself, is not founded on a knowledge of the circumstances of the death, but on the reverse of knowledge on complete ignorance of all the causes or conditions which preceded the accident and caused it. Let us suppose a man to have died suddenly, and a number of circumstances to point to the conclusion that he has been poisoned. A legal investigation, dissection, and chemical search, is ordered ; but no sign of poisoning, no trace of poison, is found. If now, on the ground that more than a hundred years before, a poison existed, the Aqua Tofana, with which many men were poisoned a poison which causes death and eludes all research, leaving no traces of its action ; if, I say, the experts were to offer this expla- nation, that the absence of all signs indicating the cause of death showed that death had been caused by this Italian poison, what would a reasonable man say to such an opinion, in such a case ? And what would he say, if to the question, What, then, is the Aqua Tofana 1 he received the answer, that no one knew, that there were many things which we 304 LETTERS ON CHEMISTRY. did not know, without being compelled to doubt the existence of the Aqua Tofana ? Those who assume death to be caused by spontaneous combustion place themselves exactly in the position of the experts. There is found, in a room, a woman or a man, dead, and burned. The experts are ordered to make a report on the case, but cannot discover in what way the fire occurred, or how it was propagated in the body ; nor can they give any account of the degree of the burning or destruction of the body ; and since for more than a century cases very similar have occurred, in which it was supposed to be true that the combustion originated spontaneously, or that the body was set on fire by an external cause, and then continued to burn, they classify the present case with the others, and explain it in the same way as the others have been explained. Because they could not discover that the death had been caused by external causes, and the destruction of the loodj had been effected by burning fuel applied to it ; from utter ignorance, therefore, of all which preceded the death, they deduce a positive cause, for the very existence of which all proof is wanting ; which is not only in the highest degree doubtful, but which also contradicts the best known laws of the burning and of the combustibility of animal bodies. To explain an occurrence which is not understood, they fly for aid to a cause which itself is not understood. Instead, therefore, of saying that the case before them, for want of sufficient knowledge, is unexplainable, they maintain that this want is a proof that spontaneous combustion has taken place ; a phenomenon which also, from want of sufficient knowledge, they are unable to explain, but which must be true, because similar cases have been so explained for more than a hundred years. The insufficiency and error of such a conclusion hardly requires to be more distinctly pointed out. The authors who have expressed and defended the opinion, that spontaneous combustion exists and must be admitted, are not persons who by their position and their occupation AMOUNT OF FUEL UNKNOWN. 305 were so placed as to become intimately acquainted with the action of fire on animal bodies, such as cooks, male and female ; but have usually been persons who had no oppor- tunities of practically acquiring this knowledge. The proofs which they adduce are taken, contrary to all the rules of logic, from the case itself. The death and destruction of the body, the cause of which is to be dis- covered, are adduced as proofs that the imagined cause is the true one. By the existence, thus assumed, of spontaneous com- bustion, the cases are explained ; and these same cases, which really require to be explained, are adduced as proofs of the existence of spontaneous combustion. As another main argument for spontaneous combustion, is adduced the fact, that in the majority of cases the body has been destroyed or consumed in such a degree, that we cannot suppose enough of fuel to have been present, external to the body, to produce the actual effect. Consequently, and precisely for this reason, an internal cause, in the body itself, must have contributed to the result ; that is, the body must have supported the combustion by its own mass. With respect to the fuel, assumed to have been present in insufficient quantity, this is a very insecure supposition ; for fire, the cause of death by burning, has this peculiarity, that it consumes the fuel or matter which supports it, so that the fuel does not remain unaltered, like the knife with which a man has been murdered. We cannot therefore possibly judge, after the burning, how much fuel has been present before it ; for that which remains is only a part of the whole of the fuel which has acted ; and it is precisely that part which has disappeared, or has been consumed, that produces the effect. With regard to the writers who defend the theory of spontaneous combustion, or the conscientiousness and trust- worthiness of their statements, we must, above all things, consider their capacity for forming a judgment. To have this capacity, a necessary previous condition is, that they have the required knowledge. They must know what 306 LETTERS ON CHEMISTRY. combustion in general is ; and what takes place in it ; they must have observed the cases, and must really have had the sincere intention of investigating the process, and of ascertaining everything that can assist in explaining the occurrences, without any preconceived opinion. When we apply this measure in judging of the trust- worthiness of the writers on spontaneous combustion, of all that they assert and believe, nothing remains but the narration of a death or of a number of deaths, by burning. I have already mentioned, that not one of them was present during such a combustion ; and they take the cases, which they relate, either from unauthenticated newspaper notices, or they relate them after other narrators, who, like themselves, have seen none of the cases. All of them, without exception, assume the existence of spontaneous combustion as true ; and they are occupied, not in investigation and testing, but in showing how the occurrence, which of course they did not see, took place. These circumstances clearly show in what stage of culti- vation these men stand, and how little qualified they are to give a valid judgment on these occurrences. As a general rule, the cases narrated by others, unattested as to the mode of occurrence, are used by them to support a theory imagined by themselves. That which, in the stories, favours the theory, is brought out, and all that opposes or refutes it, is either passed over in silence, or designated as secondary in importance. These men do not strive to ascertain the existence and the truth of spontaneous combustion ; they are advocates for the opinion or theory, that spontaneous combustion exists. We cannot wonder that, fifty or a hundred years ago, there were distinguished : physicians, who believed and defended the spontaneous combustion of the human body, at a time when the essence and nature of combustion, generally, was hardly known ; but the modern authors who defend this opinion, are, for the most part, men, whose qualifications for judging, or whose powers of observation, THE PROOF IS DEFECTIVE. 307 and whose possession of the necessary knowledge, are not proved by other genuine scientific labours or investigations in their department of science, and whose names are only known because they have appeared as defenders of the opinion in question. The distinct and unhesitating way in which, in many works on medical jurisprudence, the known cases are related and the different theories of spontaneous combustion are explained, has had the bad effect of inducing many well- informed practical physicians, contrary to their better conviction, to allow spontaneous combustion to pass for established truth, and not to contradict the statements and opinions of the supporters of that theory, in order to avoid being regarded as heretics in medicine. Every one now knows that, when, in these days, a man is accused of having poisoned another, above all and before all, the poison must be detected, and it must be proved that the accused has used this poison to accomplish his criminal intention. In times, in which the means of detecting poisons with the greatest certainty were not yet known, the rack was used to make the discovery. It is hardly necessary to remind you, that this instrument was employed with so much success, that thousands of human beings confessed that they could exercise sorcery and witchcraft. The stake no longer stands ready for sorcerers and witches, not because it has been proved that there are no witches or sorcerers, but because the enlightened study of nature has succeeded in demonstrating that all the things of which these unfor- tunate victims of ignorance and superstition were accused, must be ascribed, not to the devil, but to natural causes. These thousands were judicially murdered on the scaffold, or at the stake, by the advocates of the opinion, that sorcery and witchcraft, as the results of a compact with the evil one, are possible and really exist. But when, at a later period, the reasons for this opinion were inquired into, and all the facts on which it rested, accurately and conscientiously examined and tested, it appeared that everything which appeared to support the popular opinion rested on false or x 2 308 LETTERS ON CHEMISTRY. fallacious observations on fallacious explanations on error or on deliberate falsehood. Precisely so is it with the other reasons, collected from experience or from science, with which the defenders of the theory of spontaneous combustion strive to support it, and to prove or render intelligible the supposed process. The reasons derived from experience are in part true, but do not apply to the cases. Those taken from science, the so-called theoretical reasons, are, without exception, fallacious, and also fail to explain the cases. Thus, for example, a butcher in Neuburg, ninety-nine years ago, had an ox which was sick and much swollen. When opened, there flowed out of the belly an inflammable air, which was kindled, and then burned with a flame five feet high. The same thing was observed by Morton in a dead pig, by Ruysch and Bailly in dead human bodies, which had been swollen in an extraordinary manner by the dis- engagement of gases. Resting on these facts, the adherents of the theory of spontaneous combustion assume that disease may produce a state of body in which a combustible gas is disengaged, which accumulates in the cellular tissue, and, when kindled by an external cause, by a flame, or by the electric spark, effects the combustion of the body. We may easily perceive that the conclusion has no connection with the facts on which it is grounded. 1. The accumulation of gas in the cellular tissue has only been observed in dead bodies, and indeed in such as were far gone in putrefaction and enormously swollen. Besides, the gas did not, in these cases, escape through the skin, till a cut was made through skin and cellular tissue. Lastly, the gas indeed burned when kindled, but the body was not thereby kindled ; it' had not become spontaneously combustible, or indeed combustible at all, and was not burned. 2. In such as are supposed to have died from spontaneous combustion, a swollen state, such as is caused by accumu- lation of gas, has never been observed j but they were per- fectly healthy. PHOSPHURETTED HYDROGEN. 309 The explanation in question is, therefore, obviously en- tirely untenable. Another writer assumes that in certain diseased states a gas, phosphuretted hydrogen, is produced, which takes fire on contact with air ; and that the spontaneous and easy combustibility of the body must be ascribed to this very easily and spontaneously combustible substance. There exists, indeed, such a gas, phosphuretted hydrogen, which takes fire instantly on mere contact with air; but this gas loses that property by a short contact with gypsum, charcoal, paper, oil of turpentine, &c. ; and with regard to its presence in the human body, it has never been observed, either in health or in disease, nay, not even in the putrefac- tion of dead bodies ; and what is more important, the human body contains no phosphorus in such a state as to- yield by any process, during life or after death, phosphuretted hydrogen gas. The fact of the existence of phosphuretted hydrogen is undoubted ; but its formation and its presence in the human body are certainly false ; no observation whatever speaks in favour of its formation there. This gas, again, is in the highest degree poisonous, as much so as arsenic; and its presence in the blood of a living animal is quite irrecon- cileable with this property. Others again ascribe the assumed easy combustibility of the human body to the presence of an unusual proportion of fat, or to the circumstance, that from the abuse of ardent spirits, it is, as it were, steeped in spirits, r and therefore burns like a candle or a spirit lamp, when kindled from without. This notion depends on -an erroneous conception of com- bustibility, or on ignorance of the conditions of combustion. We cannot render a substance which burns with difficulty easily combustible by means of one of easy combustibility, but only by removing the cause which renders it difficult of combustion ; or by increasing its surface, and consequently the access of air, which is indispensable to the process. When we steep a sponge or clippings of paper in brandy, or spirits of wine, and kindle the latter, the sponge and the 310 LETTERS ON CHEMISTRY. paper are not found more combustible than they were by themselves. The brandy burns away, and then the paper perhaps takes fire, but never till all the brandy has been burned off, and then not better than if it had not been steeped in brandy. The sponge, under these circumstances, does not burn. In like manner, when a piece of flesh is thrown into boiling fat, and the fat is kindled, the fat burns, but not the flesh. It is not kindled, and does not continue to burn, even when the fat is all burned. Flesh is riot rendered easily combustible by the presence of fat. Every one knows that a wisp of straw burns easily. The cause of this is its loose texture, in consequence of which every straw is surrounded by air. But when the straw is chopped into small pieces, it burns with difficulty ; nay, it may be used to extinguish a fierce fire, by throwing on the fire so much chopped straw as covers the fuel completely. The burning body ceases to burn, because by the chopped straw the access of air is prevented. When brandy is poured over a plum pudding and kindled, the brandy burns, but when it is all consumed, the pudding does not take fire. Cotton, which when loose is easily combustible, becomes in the form of a wick difficulty combustible in an oil lamp. It is burned and charred only where the air has access to the wick. We can render paper clippings or sponge easily combustible by steeping them in a solution of saltpetre, and drying them ; that is, by a substance which is not itself combustible. But we cannot do this by means of an easily combustible substance. The presence of alcohol, or an excess of fat, cannot then give to the human body an easy combustibility which does not belong to it naturally. . To burn the body in that state fire must be applied from without, and must continue to act on it, after the brandy and the fat are consumed. Dry animal substance, such as flesh, is not in itself difficiilt of combustion ; indeed up to the charring point it is easily combustible, as may be seen in a piece of horn, or in shavings DRIED FLESH IS COMBUSTIBLE. 311 of horn. Even bones may be kindled by a small fire, and will then continue to burn if placed in heaps, without further application of external fire, till they become as white as chalk, being reduced to ashes. Flesh dried, that is deprived of the greater part of its, water, behaves exactly as horn does. Tissues and membranes also when dry are easily destroyed in the fire. All these substances become difficult of com- bustion in consequence of the water they contain in the fresh state, which in the flesh and other soft parts amounts to 75, and in the blood to 80 per cent. The water is con- tained in these tissues as in a sponge, the pores of which are very fine. It cannot, as is well known, be heated in the open air, even by the fiercest fire, beyond its boiling point. But this temperature, 212 Fahr., is very far from high enough to kindle the animal matter ; even fat requires, tor kindle it, a temperature of about 800 Fahr., about four times higher than that of boiling water.* All substances, the kindling heat of which lies higher than 212 Fahr., become difficultly or rather not at all combustible when in a porous form, and steeped in water ; for so long as water is present the combustible body cannot burn, even in the fiercest fire. Only when the water has been boiled off, does the temperature of the substance rise higher, and at the kindling point it bursts into flame, t It is therefore, easy to see how even the presence of fat does not render the body easily combustible ; for so long as it retains any water, the fat does not take fire, because, for that, a higher temperature is required. The fat melts and * No one considers white of egg combustible ; because every one knows that the water which renders it fluid is not combustible, and that burning bodies are extinguished when covered with water. Coagulated albumen is not more combustible ; for it retains almost the whole water. Now the water in soft animal tissues is in the same state as in coagulated albumen ; and these parts, from containing so much water, cease to be combustible. f When wet paper is held over a spirit flame, the paper will not burn till all the water is dissipated. The dry parts burn ; those which are still wet do not. The paper does not burn on, because the heat is not sufficient to dry the part nearest that which is burning, and to raise it to the kindling point. But the essential condition of continued burning is, that the burning part shall give to the next the necessary temperature. 312 LETTERS ON CHEMISTRY. runs out, and when the heated animal parts have lost their water by evaporation they would be kindled and burst into flame, even if no fat were present. The presence of fat, since it also barns, makes the flame larger, but does not render the flesh more combustible. The body can only be rendered rapidly combustible by the addition of highly oxidised substances ; thus, by means of nitric acid, cotton, linen, and sawdust become so exceedingly easily kindled and so very combustible, that they may be used instead of gunpowder. No special theory is required to enable us to see that the fat of an animal body exposed to the fire, when it flows into the fire and burns there, contributes to the further destruction of the body. The flame of burning fat of course acts on flesh just as does the flame of burning spirits ; and every one knows that with the latter we can produce the same effects as with wood or coals. In the living body one circumstance opposes its being set fire to and burned, which is absent in the dead body; namely, the circulation of the blood. In a piece of flesh acted on by fire, the fluids which moisten it remain where they are till evaporated ; but in a living body there flows through all, even the minutest parts, a current of blood which causes this result, that the heated portions are con- stantly earned away and replaced by cooler portions. If the fire without be very fierce, a reaction takes place from the blood, consisting in a flow of water outwards towards the heated point. The skin is detached from the subjacent parts, and a blister, full of water, is thus formed. So long as the current of blood continues, the body may be injured by external heat ; but it cannot burn, or become burned or charred, till the circulation has ceased ; that is, till death has taken place.* * Many of the adherents of the theory of spontaneous combustion admit that in the healthy state a living body cannot take fire of itself and burn ; they assume that there exists a morbid state, in which, as products of dis- eased action, compounds are formed of much greater inflammability than is usually possessed by animal matters. This is a mere fancy, without even THE ELECTRICAL THEORY. 313 Spontaneous combustion in a living body is therefore absolutely impossible. Even phosphorus, a body so eminently combustible, loses, under similar circumstances, its com- bustibility; as when it is prepared for matches, and its particles, in a fine state of division, are surrounded by particles of water. That excess of fat, or the presence of brandy in the body, is not the cause of easy combustibility, and does not render the body easily kindled, is most strikingly demon- strated by the fact, that hundreds of fat, well fed brandy- drinkers do not burn, when by accident or design they come too near a fire. It may with certainty be predicted that, so long as the circulation continues, their bodies would not take fire, even if they held a hand in the fire till it was charred. The most remarkable theory is one which supposes that spontaneous combustion is caused by electricity, or by the electric spark. Muncke, formerly Professor of Physics in Heidelberg, says on this point in Gehler's Physikalisches Worterbuch, vol. x. p. 262: "In these matters electricity must, before all things, be excluded from the explanations ; for nothing determines its increased development, and, as no isolation exists, this is rather to be regarded as impos- sible ; and we have no such electrical spark as is required to kindle combustible matter." The theory in question is the shadow of observation to support it. All nitrogenous bodies require for combustion a higher temperature than carbon or hydrogen. It is a peculiarity of these bodies, that by containing nitrogen they lose in a great measure their inflammability. On this account, nitrogenised compounds are not reckoned among combustibles. Ammonia, a compound of nitrogen and hydrogen, is no longer combustible ; it cannot be kindled by a red-hot body, and does not burn. Even phosphorus, in the phosphide of nitrogen, loses its inflammability. We cannot imagine a nitrogenised body which, by transformation, should yield compounds more inflammable than hy- drogen, which requires a red heat to kindle it in the air. A man, weighing 120 Ibs., has about 901bs. of water in his body. If we suppose this water in a boiler, and the solid parts, bones, flesh, &c., to be burned dry under it, then, even admitting that they should take fire when heated and continue to burn, like wood, the heat given out by their carbon and by the hydrogen which is not expelled in the form of ammonia, is not enough to convert into vapour all the water in the boiler. 314 LETTERS ON CHEMISTRY. founded on a statement made by the traveller Brydone, that he knew a lady whose hair became so electrical by combing it, that whenever it was combed sparks were seen. Another fact is, that a senator, named Drayton, in the United States, observed electrical sparks when drawing off his stockings, whether of wool or of silk. These facts are true, they are of every day occurrence ; but the use made of them by the defenders of the theory of spontaneous com- bustion appears to be at least absurd ; for the property of hair or of silk to become electrical by friction, belongs, not to the body, but to every wig and to every stocking. The electricity does not proceed from the interior of the body, for the hair when cut off, or the stocking when removed, equally possesses it. The body is, on the contrary, the greatest obstacle to the observation of the electricity of. these substances ; and it is only in rare cases that the skin is so dry, or of such a quality, that the hair or silk becomes electric by friction, in spots of their contact vv'ith the skin. This property of developing electricity has never been observed in the body of persons supposed to have perished by spontaneous combustion, either before or after death, and when sparks have occurred, the hair or silk has never once been set fire to. I cannot better characterise the opinions alluded to, and the persons who regard spontaneous combustion as an histo- rical truth, and defend it, than by quoting the theory of one of its latest supporters, F. J. A. Strubel, in his work, " The Spontaneous Combustion of the Human Body, with especial reference to its medico-legal significance. A treatise, writ- ten under Prof. Dr. J. Wilbrand, Ordinary Public Teacher of Medical Jurisprudence in the University of Giessen, and laid before the medical faculty there. Giessen, 1848." This theory is as follows : ^-On the ground of Brydone's observation, he proceeds " If, in the human body, the deve- lopment of electricity, from whatever cause, is so increased, or the electricity so accumulated or condensed, that it ' is discharged outwards in sparks, spontaneous combustion may occur, and that for the following reasons : the electric sparks. THE ELECTRICAL THEORY ABSURD. 315 traversing the body in all directions, must not only decom- pose, to a greater or less extent, the water which constitutes four-fifths of the body, but must also kindle the products of its decomposition, its elements, oxygen and hydrogen, whe- ther this be caused by mechanical compression or by chemical action, a point on which men of science differ. But oxygen, when mixed with hydrogen, and kindled, as in the cases before us, produces the most intense heat, in which the diamond is easily dissipated. According to this explanation, that which formerly appeared most marvellous, namely, its extraordinary rapidity, the shortness of the time in which it takes place, is at once understood ; and we can only feel sur- prised if the contrary occur. It would also explain how the fat of the body may be set on fire, and continue to burn." This theory is a pattern of its kind. Its author has not the remotest conception of the laws of the production and accumulation of electricity, of the conditions of the forma- tion of the spark, of the decomposition of water by electricity. It is sufficient here to observe, that when electricity decom- poses water, no spark ensues ; and when a spark ignites the gases, water is formed, and not decomposed into its elements. But, assuming everything to happen as he imagines, that water is decomposed, and that the elements, by the decom- posing agent, are again converted into watei*j the body, by the kindling of the gaseous mixture, would, in less than a second, burst into thousands of fragments, like a mortar filled with gunpowder ; and yet it would not burn, in spite of the high temperature, because the whole of the oxygen is at once seized by the hydrogen, and no free oxygen remains for the combustion of the body. Oxygen and hydrogen, when pro- duced by the electrical decomposition of water, form the so- called explosive gas, distinguished by the property of explod- ing with a violent report when kindled. A hollow ball, of small size, made of paper or of swine's bladder, and filled with this gaseous mixture, explodes, when kindled by an electric spark, with a report as loud as that of a cannon ; but the paper and the bladder do not take fire nor burn. With respect to the extraordinary rapidity of the sup- 316 LETTERS ON CHEMISTRY. posed spontaneous combustion, this is a mere invention ; for in the cases in which persons have been found dead, nothing whatever is known of the course of the accident. The same remark applies to the character of the flame, which is said not to be extinguished by water. All the evidence for this rapidity of combustion and inextinguish- able flame is derived from one case which was described, not by a physician, not even by a surgeon of those days, nor by a bather, but by a priest named Boineau. It was that of a woman of eighty, who drank nothing else than spirits. She began to burn, sitting on a chair, and burned, although water was poured upon her, till all the flesh was consumed. The skeleton alone remained, sitting in the chair. This case is related in a letter dated the 22nd of February, 1749, and is therefore one hundred and one years old. The narrator was not present, and did not see the flame ; and the story plainly indicates a good intention on his part, that of inoculating his flock with a wholesome terror for brandy-drinking. This explains the resemblance between the flame of the burning- tippler and hell-fire. The chair, which had not sinned, of course did not burn, and was only slightly singed on the surface. The notion of the rapidity of the combustion, and the peculiar character of the flame, assumed in the remaining forty or fifty cases, rest on this case alone ; for, in all others, the people were found burned to death, who had been seen alive five, six, or twelve hours before. Nothing more is known of these cases. The most striking proof of ignorance of the laws of com- bustion, and of incapacity to form a judgment on the cases of supposed spontaneous combustion, in the defenders of that notion, is this, that they lay the greatest stress on cir- cumstances quite insignificant, which have no relation to the question ; while they regard as non-existent the most important facts. This is the case, for example, with the vapours, smoke, and smell which fill the room in which burned persons are found, and the viscid, brown, greasy deposit which is observed on all the furniture, window-panes, SOOT AND TAR FROM BURNING FLESH. 317 mirrors, &c. All this is regarded as a peculiarity and dis- tinctive sign of spontaneous combustion. Now, this deposit, as every one knows, consists of solid combustible particles, and of liquid products, formed by the action of heat on animal and vegetable matters, such as flesh, blood, paper, &c. ; but, of course, only when these particles have not burned ; for these solid and liquid portions are very com- bustible, and their non-combustion depends on a want of oxygen, and of the temperature necessary for their taking fire. The solid parts of smoke are called, in general, soot : the liquid parts are called tar. The deposit on the furniture and windows is a thin coating of animal soot and tar. Like these, it feels greasy, and is exactly like the coating which is at first formed in the chambers where meat is smoked, and which covers the meat itself. With a little of what is called in German " Glanzrass," or lustrous soot, which is a kind of lamp-black riot freed from oil or tar, when mixed with water, we can give to glass and wood the same coating ; only here we see the strokes of the brush, which, of course, are absent when the deposit settles uniformly on objects from the air. Moreover, among the products of the action of heat on animal matter, is a compound of sulphur (sulphide of ammonium), which renders white-lead paint brown or black. These products, soot, tar, &c., are formed when heat acts on combustible animal or vegetable matters, which do not burn (as in the dry or destructive distillation, and in the making of vegetable or animal tar), and are an irresistible proof that the parts which yield them have not undergone combustion ; for had they done so, and had air enough been present, they would have been consumed ; that is, entirely oxidised ; and nothing would have remained capable of forming a deposit on glass or furniture. It is in the nature of the thing that a person who has now and then smelled rose-water, and remembers its odour, shall be able, in many cases, to distinguish rose-water from eau de Cologne ; but to assert that by the smell which fills a room we can tell whether it arise from spontaneous com- bustion or not, or that we can discover whether the deposit 318 LETTERS ON CHEMISTRY. on the furniture arises from a body which has spontaneously taken fire, and not from leather (the covering of cases, &c.), paper, wood, hair, clothes, &c., all of which have been also exposed to heat and this, too, when the observer has never had an opportunity of becoming acquainted with the pecu- liarities of the smell or the deposit from a body which has really undergone spontaneous combustion, if such pecu- liarities there be, and consequently without a recollection of these things such assertions as these go far beyond any- thing that we can ask a man of sense to believe. It is nothing short of an insult to the healthy human under- standing. The conclusions to which the theory of spontaneous com- bustion leads are in such decided contradiction with all experience, that the explanation offered by the adherents of that theory has not met with the smallest acceptation on the part of one distinguished physician in any degree acquainted with the natural sciences. As long as medicine has existed, no case has ever occurred in which a married couple at the same instant have been seized with inflamma- tion of the lungs, or any other disease, and in which, in both man and wife, the disease has run the same course, and both have died at the same moment. How many improbable suppositions in regard to the state preceding invasion of the disease must be made before such a result can be supposed possible ! Now, the adherents of spontaneous combustion find this quite in the natural order of things, in regard to the disease or morbid state which precedes the combustion ; for they relate a case in which a tailor, named Lariviere, with his wife, both being intoxicated, after having been left at seven in the evening, were found, at eleven next day, con- verted into a shapeless charred mass, with the exception of some fragments. The man who can ascribe such an occur- rence to disease, or to a morbid cause, must find it an easy task to swallow a camel. That several persons, in a room where the vapours of burning charcoal accumulate, are suffocated at the same time, is a case, unfortunately, which only too often occurs. SUPPOSED RAPID AND PAINLESS DEATH. 319 The adherents of spontaneous combustion regard it as a peculiarity of that process, that when it happens no cry for help is heard (obviously because the victims are dead before they are burned). This is just as if we were to regard it as a peculiarity of burglary that the people of the house do not hear the noise made by the thieves in entering it. Such a robbery only succeeds when the people of the house do not hear the noise ; that is, when they are absent or asleep ; and of course a man can only be burned to coal and ashes when no one hears his cries for help. If people were near, and if he were able to cry for help, he would not be allowed to be burned to death. It has been concluded, from the fact of no cry being heard, that the death is not only rapid, but painless ; and in this case we can only wonder that such a pleasant death is not desired for all good Christians, since all must die of some disease, and spontaneous combustion, on this theory, is a disease, although an unusual one. In order to explain why a particular part is burned, it is of course always assumed that the seat of the disease was in that part. If the abdomen and intestines are burned, the disease was in the belly ; if the head and neck are burned, the disease was in them ; and it was in the arms and legs when they suffered. Wherever the effect appears, the cause is placed, and the presence of the cause is explained or proved by the effect. This is contrary to all the rules of logic. The theory is so elastic, that it can be made wide or narrow, just as we require it. If the burn is severe, the disease was severe ; if the burn is superficial, so was the disease. Two square inches of skin on the leg are diseased, and set fire to the trousers ; but all round this spot the skin is quite healthy, as in other men. If unconsciousness be required, it is there ; but if, with the head on fire, conscious- ness is wanted for certain actions it also is there. When it has been ascertained, as far as such a thing can be ascertained, that the person burned was never intoxicated, and had a horror for brandy, then it is insinuated that he probably 320 LETTERS ON CHEMISTRY. drank in secret. We see how error and this theory is an error only produces delusion, contradictions, and new errors. There is only one path to the truth, crossed by a thousand crooked paths, at each of which credulity stands to point the way. Truth has its rights, which cannot be infringed with impunity : it has its signs, by which every unprejudiced man recognises it. The defenders of this theory explain why a part of the clothes on the burning body is not burned, by one cause or another ; it is a peculiarity which has been observed in this phenomenon. And when the burning body, which did not set fire to the clothes, sets fire to a bureau or a sofa, this is explained by other causes. The clothes are burned above, on the breast, and there the flames acted like other flames ; but below the epigastrium the clothes did not burn ; this is the result of the peculiar quality of the flame ! It is impossible for any one who was not present to explain the most trifling and insignificant specialities in such cases ; and to demand such an account of these is foolish ; for to explain them presupposes a knowledge of the whole occur- rence, and that is unknown. Many of these specialities depend on causes which are never again combined, and which are on that very account called accidental.* From what has been said, I trust that the reader will be enabled to appreciate the true value of the opinion, as well as of the cases of spontaneous combustion ; and to see why science has paid no regard to such a theory, destitute of every shadow of foundation. The close relation between spirit-drinking and death by burning is so obvious, that it is hardly necessary further to allude to it. In the case of a person intoxicated, deprived * If any one, for example, throws a- sixpence into the air, it may happen that it falls into a chink of the floor, and presents to us its edge, and stands upright. But if the same person, in the same room, throws up the same coin a hundred thousand times, it may occur that it never once falls into the chink, and, even if this were to happen a million of times, it might never fall into the same spot of the chink. We cannot, with the best in- tentions, bring together the conditions necessary for this result ; the coin falls on another spot. This kind of events is ascribed to chance. CAUSES OF FIRE. 321 of all reflection, and incapable of all judgment concerning danger, and what is connected with it, we may suppose any proceeding, even the most unlikely. We may imagine that in this state a man on going to bed, and extinguishing his candle, sets fire to the bed and curtains ; that he goes to bed in winter near a closed stove, and with a pan of burning charcoal ; or in looking for a boot-jack under the bed, he may leave the light which he used standing under the bed. Innumerable suppositions equally probable, sufficiently account for the breaking out of fire in a room, in which there is a human being and also a light ; and if the person be still completely intoxicated, the danger is increased in the same proportion as his accountability is ^diminished. He is like a child that has no idea of the action of fire. Three years ago, an unfortunate drunkard, in the neighbourhood of Oxford, crept on a lime-kiln to sleep, and had the limbs burned from the feet upwards, in a dreadful manner. Such is the true relation between spirit-drinking and burning. All that is said of flames from the throat of drunkards is entirely false. No one has ever seen these flames the man who tells the stoiy has always had it from another narrator ; it is only certain, that compassionate street vagabonds, when they find a man dead drunk, often employ the liquid that drips from dunghills to extinguish the internal fire, against which it is said to be a sovereign remedy. Exact experiments, made with this object, have proved that air, saturated with the vapour of alcohol at blood heat, cannot be kindled, and does not burn with flame. When fire occurs in a room or in a house, the proprietor and the insurance companies have the greatest interest in ascer- taining how it arose, and who caused it. In most cases, this is not ascertained, because he who purposely sets fire to a house does not confess to doing so ; neither does he who does it from carelessness. But when the cause remains unknown, no one believes that it has broken out spontaneously, and without the aid of some person.* And if a cat be found * Except in cases where masses of charcoal powder, or tow and cotton T 322 LETTERS ON CHEMISTRY. burned to death in the room, no one will imagine that the fire has arisen from the spontaneous combustion of the cat, or suppose, because a cat's fur sometimes becomes electric by rubbing with the hand, that a disease exists among cats, by which they become spontaneously combustible. Yet this supposition is not more improbable than in the case of men. It may be said that cats drink no brandy ; but the defenders of the theory of spontaneous combustion admit, that the body has frequently taken fire spontaneously in persons not addicted to ardent spirits. In cases of fire, when the investigation is extended to all those who had access to the place where it broke out, it often happens that the incendiary, or the accidental originator of the fire is discovered. Legal medicine, even if the theory of spontaneous combustion were true, which it is not, ought not to interfere in so simple a proceeding, justified as it is by experience, until all other probable causes of fire have been excluded ; and if this be, notwithstanding, done, those who so act deprive legal medicine of its proper rights, and become partakers of the incendiary's guilt ; they protect the criminal by misleading the investigation. The physician, who is called on for a judgment in such cases, can only say, if he act according to duty and conscience, in what state the body was found, whether the injury from burning took place before or after death, whether death was caused by fire alone, or before the action of the fire by other causes, such as wounds, strangulation, a blow on the head, &c. In no case is it permitted to him to explain anything he has not seen, by cases which he has also not seen, or by a theory which he cannot understand. steeped in oil, as often happens in certain manufactories, are set on fire by the oxidising agency of the atmosphere. W. G. PROSPECTS OF PHYSIOLOGY. 323 LETTER XXY. Hopeful prospects of Physiological Science if pursued inductively Mutual relation of natural laws Physical and Chemical Variation of the density and boiling points of liquids according to the variations in their composition Examples Relation of Specific Heat to Composition ; and to the velocity of sound in gases Relation of Electric Currents to Magnetism, Heat, Chemical Action, &o, Vital properties related to other properties of matter Progress of Anatomical Physiology Anatomy studies the apparatus, but cannot explain the process without Chemistry Province of Chemistry Examples of Chemical explanations of Physiolo- gical facts ; as in the Chemistry of the Urine Method of determining Chemical formulae Their true meaning. THE history of science gives us the consoling assurance, that we shall succeed, by pursuing the path of experiment and observation, in unveiling the mysteries of organic life, and that we shall be enabled to pbtain decided definite answers to the question What are the causes which have a share in producing the vital phenomena ? All the peculiari- ties of bodies, all their properties, are determined by the co-operation of several causes ; and it is a problem to be solved by scientific research, to ascertain the proportion in which each individual cause contributes to the effect. In order to attain a knowledge of the mutual relations of these properties, we must endeavour to become acquainted with them, and to discover the cases in which they vary. It is a natural law, which admits of no exception, that variations in one property are always and invariably accompanied by uniform and corresponding variations in another property, and it is perfectly obvious, that if we know the laws of these variations, we are enabled to deduce one property from the other without further observation. To ascertain a natural law, is nothing more than to ascer- tain such a relation of dependence. Knowledge of the law Y 2 324 LETTERS ON CHEMISTRY. includes explanations of the phenomenon, and an insight into the essence of the forces, by which it is determined. It is known, that every liquid, under the same circum- stances, boils at a fixed temperature. This is so constant, that we regard the boiling point as a characteristic property of liquids. One of the conditions which determine the constant tem- perature, at which, in the interior of liquids, bubbles of vapour or gas are formed and rise unchanged, is the external pres- sure. The boiling point varies with the pressure in all liquids, in each according to a special law. It rises or falls, when the pressure is increased or diminished. A certain pressure corresponds, in any liquid, to each boiling point, and a certain boiling point to each pressure. The know- ledge of this law of the dependence of boiling point on the atmospheric pressure, has led to a method of measuring elevation above the level of the sea ; that is, to measure one property by the variations of another. The relations in which the boiling point of liquids stands to their composition, are less generally known. Wood spirit, alcohol, and the oil of potato spirit are three liquids of very different boiling points. Wood spirit boils under the pressure of 30 inches of the barometer, at 59 C. ; alcohol at 78 C. ; potato oil at 135 C. The comparison of these three tem- peratures shows that the boiling point of alcohol is 19 C. higher than that of wood spirit (59 + 19 = 78) : while that of the oil of potato spirit is four times 19 higher than that of wood spirit (50 + [4 x 19] = 135). Each of these three liquids yields, by oxidation, under the same circumstances, a volatile acid j from wood spirit is obtained formic acid ; from alcohol, acetic acid ; from oil of potato spirit, valerianic acid. Of these three acids, each again has a constant boiling point ; formic acid boiling at 99 ; acetic acid at 118 ; and valerianic acid at 175 C On comparing these temperatures, we at once see that they bear to each other a relation similar to that observed between the boiling points of the original liquids. The boiling point of acetic acid is 19 higher than that of formic acid; and COMPOSITION AND BOILING POINT. 825 that of valerianic acid is four times 19 higher than that of formic acid. A uniform variation in one property corre- sponds, as we shall see, to a uniform variation in another property. One of the properties, in this case, is the com- position. If we compare the composition of the six bodies, the three alcohols, or original liquids, and the three acids formed from them by the action of oxygen, we obtain the following results. The composition of wood spirit is represented by the formula, C 2 H 4 2 ; that of alcohol, by C 4 H 6 2 ; that of the oil of potato spirit, by C 10 Hi 2 2 . If now we designate by R, a weight of carbon and hydrogen, corresponding to the symbol C H, that is, one equivalent of each, we see at once that the formula of alcohol is equal to that of wood spirit, -f 2 R. Wood spirit. Alcohol. C 2 H 4 2 +C 2 H 2 = C 4 H 6 2 The formula of the oil of potato spirit (Amylalcohol) is equal to that of wood spirit, -f- 8 R. Wood spirit. Amylalcobol. C 2 H 4 2 + C 8 H 8 = C 10 H 12 2 The formula of formic acid is, C 2 H 2 4 ; that of acetic acid is C 4 H 4 4 ; that of valerianic acid is Cj Hi 4 . It is easy to see that the formula of acetic acid is equal to that of formic acid, -f- 2 R. Formic acid. Acetic acid. C 2 H 2 4 + C, H 2 = C 4 H 4 4 While that of valerianic acid is equal to that of formic acid, + 8 R. Formic acid. Valerianic acid, C 2 H 2 4 + C 8 H 8 = C i0 H 10 4 According to these facts, the entrance into such a com- pound, or the addition to its elements of two equivalents of carbon and two of hydrogen, or of 2 R,, corresponds to a rise 326 LETTERS ON CHEMISTRY. of 19 C. in the boiling point. It may be proved that this relation in the group above described is quite constant, and that from a knowledge of the boiling point, we may deduce, backwards, the composition of the liquid. The boiling point of the formiate of oxide of methyle (oxide of methyle is C 2 H 3 0, the ether of wood spirit), is 36 C. ; that of the formiate of oxyde of ethyle (common ether, or oxide of ethyle, C 4 H 5 0), is 55 C. Here, again, the difference is 19 C., while from this we might conclude that the com- position of the latter formiate differs from that of the former by C 2 H 2 or 2 R. This is found to be the case. The formula of formiate of oxide of methyle is C 4 H 4 4 ; and that of the corresponding compound of ethyle is C 6 H 6 4 : therefore exactly increased by C 2 H 2 . Again, butyric acid boils at 156 C, a point exactly three times 19 higher than the boiling point of formic acid ; and a comparison of the formula of the two shows that butyric acid may be regarded as formic acid -f 6 R. Formic acid. Butyric acid. C 2 H 2 4 + C 6 H 6 = C 8 H 8 4 Toluidine and Aniline are two volatile, organic bases, differing in composition, so that Toluidine contains just C 2 H 2 or 2 R more than Aniline ; Aniline being represented by the formula C, 2 H 7 N, Toluidine by C 14 H 9 N. Now, a comparison of their boiling points shows that Toluidine boils at a temperature 19 C. higher than the boiling point of Aniline. In these examples it is impossible not to recognise the existence, for this group, of a natural law ; no one can doubt that the qualities of a body stand in a definite rela- tion to its composition ; or that to a change in qualities, a un^orni variation in something quantitative is found to correspond. It deserves here to be particularly noticed, that the knowledge of such a law of nature is quite inde- pendent of that of its proper or true cause, or of the con- ditions which, taken together, produce the constant boiling point ; for what the boiling point of a liquid, considered in SPECIFIC HEAT. 327 itself is, is a matter as little known to us as the true idea or definition of vitality. In the above examples the relation between only one quality of bodies and their composition has been pointed out. But there are as many such relations as there are peculiar properties possessed by bodies. For a large group of organic chemical compounds a law has been made out, according to which, from the boiling point and the com- position, we can determine the weight of a cubic foot of the compound ; that is, the property we call specific gravity, or the pressure which equal bulks of bodies exert on that on which they rest, is found to stand in a fixed relation to two other properties, and to vary as these vary. A similar relation of dependence has been ascertained in regard to the amount of heat required by different bodies to cause in them an equal rise of temperature ; and also in regard to the properties by weight in which they combine together, that is, their equivalent numbers. It is a well-known fact that different bodies at the same temperature contain different quantities of heat. Equal weights of sulphur, iron, and lead, heated to the boiling point of water, cause, when placed in contact with ice, a certain quantity of it to melt ; and the quantity of liquid water thus produced is very different in the three cases : the sulphur melting six-and-a-half times, the iron nearly four times, as much ice as the lead does. Did these bodies contain equal amounts of heat, the weights of ice melted by all must be equal; and the inequality of effect is of itself enough to prove an inequality in the acting cause. It is perfectly certain, from experi- ment, that if we have to heat equal weights of sulphur, iron, and lead, to the same extent say from 15 to 200 C., with the same spirit flame, we should require to burn, for a certain weight of lead, for example, one ounce of spirit ; for the same weight of sulphur, six-and-a-half ounces ; and for the iron, nearly four ounces of spirit. The different quantities of heat thus required by equal weights of different bodies to undergo the same rise of tern- 328 LETTERS ON CHEMISTRY. perature, which are peculiar to them, are called, precisely for this reason, specific heats. From a knowledge of the unequal quantities of heat contained in bodies of the same weight and at the same temperature, we can ascertain, by the rule of three, the unequal weights of sulphur, lead, and iron, which contain the same amount of heat ; and it results from this calculation, that 16 parts by weight of sulphur melt as much ice as 28 of iron and 104 of lead. Now these numbers are the same which express their combining weights (equivalent numbers). Equivalents of these and of many other bodies take up equal quantities of heat in acquiring the same temperature ; and if we regard the same equi- valents as representing the relative weights of the atoms, it is clear that the amount of heat, taken up or given out by an atom, is equal for each atom, and when expressed in numbers for the atoms of different bodies, is in the inverse proportion of their equivalents or atomic weights. It is certainly a very singular result that the quantity of ice melted by a warm body in cooling, has served in many cases to correct and to fix the weights in which that body combines with others. But it will appear to many still more strange that this property of taking up or giving out heat, stands, in gaseous bodies, in quite a definite relation to the tone of a pipe or flute, produced by blowing with the gas in question ; so that a distinguished philosopher (Dulong) was able to fix, from the unequal tones, the relative amount of heat which different gases give out on compression, or absorb on expansion. In order clearly to understand this remarkable relation, we must call to mind one of the finest thoughts of La Place, in regard to the connection between the specific heat of gases and their power of propagating sound. It is well known that Newton, and many mathematicians after him, sought in vain for a formula which should express the velocity of sound in a manner corresponding to the results of observation. The calculated result was always near to the observed one ; but an unaccountable difference always remained. Since the SPECIFIC HEAT AND SOUND. 329 propagation of sound occurs by a vibration of the elastic gaseous particles, consequently as the result of a compression and a subsequent expansion of these ; and since when a gas is compressed heat is given out, and when it again expands heat is absorbed, La Place conjectured that this heat might have an influence on the propagation of sound. It appeared, in fact, that after taking into account the specific heat of atmospheric air, the formula of the mathematicians became free from all error, and was an exact expression of the ob- served velocity. If we now calculate the velocity of sound according to the formula of Newton, and therefore without regard to the specific heat of air, and if we compare the result with that derived from the formula of La Place, we perceive a difference in the length of the space traversed by a wave of sound in a second, in the two cases. This difference proceeds from the specific heat of air, from the amount of heat set free from the particles of air set in motion during the propagation of sound. It is plain that this difference in the velocity of propagation must be found greater or less in other gases, which for equal volumes contain, and, therefore, give out, more or less heat than air does ; and it is easy to see how the numbers, which express the unequal velocities of pro- pagation of sound in different gases, supply at the same time a measure for the unequal quantities of heat they contain, that is, for their specific heats. Now since the acuteness or the gravity of tones depends on the number of vibrations of a sound-wave in a second that is, on the velocity of propagation of the induced motion and since we know that in all gases the velocity of propaga- tion of the sound-wave is directly proportioned to the number of vibrations of the tones produced by it, we are thus able to explain how the specific heats of gases that is, the unequal amounts of heat they contain may be ascertained by the unequal acuteness of the tones they produce when forced through the same organ-pipe. The great discovery that musical harmony, that every tone that melts the heart, attunes it to joy, or inspires it 330 LETTERS ON CHEMISTRY. with valour, is the sign of a fixed and ascertainable number of vibrations in the particles of the propagating medium, and therefore a sign of all which, according to the doctrine of undulations, is deducible from that motion, has raised Acoustics to the rank which it now holds. Many truths regarding musical tones became deducible from the doctrine of undulation, while truths empirically obtained have led to a corresponding knowledge of the properties of vibrating bodies, formerly quite unknown. It is said of the celebrated violin maker of Vienna, that he selected the wood for his violins in the forest with the aid of a hammer, and chose such trees as when struck yielded a certain tone, known to him alone. This is no doubt a fable ; but not the slightest doubt can be entertained that he knew that the upper and under board of a good violin, make a certain number of vibrations in a second, that they give a peculiar tone, and that their thickness must be regulated accordingly. Finally, if we reflect, that the electric current, passing through a wire of metal, stands in a fixed relation to the magnetic properties which the wire acquires ; if we remember that the finest differences in radiant heat may be measured by the magnetic needle ; that the amount of electricity set in motion may be expressed in numbers by the same needle, and may also be measured in cubic inches by hydrogen gas, and in weights of metal ; when we see, that the causes or forces on which depend the properties of bodies, their power of acting on our senses, or, in general, of producing any effect that these causes or forces stand to each other in an ascertainable relation of dependence, who can any longer doubt that the vital properties of bodies, like all other pro- perties, obey this law of dependence ; that the chemical and physical properties of the elements, their form and mode of arrangement, play a definite and ascertainable part in the production of vital phenomena 1 The mere knowledge of chemical formula is not sufficient. It is necessary to ascertain the laws of the relations in which the composition and form of the food, or of the secretions PHYSIOLOGY ADVANCED BY ANATOMY. 331 stand, to the nutritive process, or in which the composition of remedies stands to the effects which they produce on the system. It is certain, that all the progress made in the physiology of plants and animals from the time of Aristotle to the present day, has only been rendered feasible by the progress of anatomy. Just as that man will remain in the dark con- cerning the manufacture of spirits, who sees no more of it than the mash, the fire, and the stop-cock from which the spirit drops, so, in truth, without an acquaintance with the apparatus, it is impossible to have an insight into the process. Now the organism, is a much more complex apparatus, which, before all else, requires an accurate knowledge of the structure of all the individual parts, before we can form a judgment concerning their value and their functions considered in reference to the whole organism. (Schleiden). But we must never forget that from Aristotle to Leuwenhoek, anatomy, by itself, has only shed a partial light on the laws of the vital phenomena ; that, so to speak, the knowledge of the distilling apparatus does not teach us its object. The same holds true of many organic processes, as of distillation ; for he who knows the nature of fire, the laws of the diffusion of heat, those of vaporisation, the com- position of the must, and that of the products of its distilla- tion, knows far more of distillation, than he who is acquainted only with the minutest details of the apparatus, and infinitely more than the coppersmith who made it. With every new discovery in anatomy, our descriptions have gained in precision, accuracy, and comprehensiveness. The restless spirit of research has reached the cell, the foundation of organised structures ; from this elevated point, a new investigation must begin. If anatomical knowledge is to serve for the solution of a physiological question, something else must necessarily be joined with it ; and the most obvious addition is that of the matter, of which the structure consists ; of the forces and properties which, in addition to the vital ones, it possesses ; a 332 LETTERS ON CHEMISTRY. knowledge of the origin of the substance, and of the changes it must undergo in order to acquire vital properties. Finally, it is indispensable to the relations, in which all the constituents of the body, fluid as well as solid, independent of their form, stand to one another. To many physiologists, Chemistry alone appears enriched by what chemists have ascertained in regard to these all important questions ; although these results, in Chemistry Proper, hold but a place as secondary as those which the analyses of minerals and of mineral waters have yielded. From the erroneous notions entertained of the influence of chemistry on the explanation of vital phenomena, proceed the errors that, on the one hand, some estimate this influence too low, while some, on the other hand, raise their expectations from, and demands on it, too high. When a decided relation between two facts exists, or is discovered, it is not the business of chemistry to prove this connection, but only to give it a quantitative expression ; to express it in numbers. By numbers alone no relation can be established between two facts, if such relation do not really exist. Oil of bitter almonds and benzoic acid are two organic compounds, altogether distinct in their mode of occurrence and their properties. A few years ago, a mutual relation between them was not even suspected. But it was discovered, that the volatile oil, exposed to the air be- came solid and crystalline, and that the new body was identical in properties and composition with benzoic acid. It was now certain that a relation subsisted between them. Observation proved, that in the conversion of the oil into the acid, oxygen was absorbed from the air, and analysis fixed the change which takes place in the shape of numbers, and thus explained it, as far as it is explainable : Oil of bitter almonds. Oxygen. Benzoic acid. C 14 H 6 2 + 2 = C 14 H 6 4 . In like manner, the study of the change produced on the CHEMICAL TRANSFORMATIONS. 333 oil of potato spirit (amylalcohol) by the action of oxidising agents, discovered and expressed in numbers a definite relation between that oil and valerianic acid, previously quite unsuspected. It was proved, that these bodies are related to each other as alcohol to acetic acid. Alcohol. Oxygen. Acetic acid. Water. C 4 H 6 2 + 4 = C 4 H 4 4 + 2 HO. Amylalcohol. Oxygen. Valerianic acid. Water. C 10 H 12 2 + 4 = C 10 H 10 4 + 2 HO Human urine contains urea, often also uric acid in the urine of some classes of animals uric acid, in that of others urea, is absent. With the increase of uric acid, the propor- tion of urea diminishes ; the urine of the foetal calf contains allantoine in human urine, oxalic acid is seldom absent. The change of certain vital operations within the body is accompanied by a corresponding change in the nature, amount, and quality of the compounds secreted by the kidneys. It is the duty of the chemist to express, quantita- tively, the observed relations in which these compounds stand to each other, and to the process going on in the organism. By analysis, chemistry first fixes the qualitative meaning of the words urea, uric acid, allantoine, oxalic acid, &c. By these formulae no relation between them is exhibited ; but when their characters and the changes which these compounds undergo under the influence of oxygen and water, the very substances which take a part in their forma- tion or alteration in the organism, are examined, chemistry attains to the expression of a decided and unquestionable mutual relation. By the addition of a certain amount of oxygen to uric acid, it is resolved into three products, allantoine, urea, and oxalic acid. By a further addition of oxygen, uric acid is directly transformed into urea and carbonic acid. Allantoine presents a composition which may be regarded as that of the urate of urea. The comparison of the conditions discovered by the chemist to determine 334 LETTERS ON CHEMISTRY. the transformation of uric acid into urea with those which accompany that change in the organism, leads to the conclu- sion, either that these conditions (in this case a supply of oxygen and of water) are the same in both cases, or that they differ. If they differ, the differences yield new starting points for research ; and when these differences are ascer- tained and reduced to their causes, the process is explained, as far as chemistry can explain it. Urea and uric acid are products of the transformation of the nitrogenised constituents of the blood, under the influence of oxygen and water. The relation between the nitrogenous bodies, uric acid, and urea on the one hand, and the oxygen of the air and the elements of water on the other, the quantitative conditions of the changes, are expressed by chemistry in formulae, and, as far as chemistry reaches, they are explained. It is evident, even to the uninitiated, that a difference in properties between two bodies depends either on a different arrangement of the elements of which they consist, or on a quantitative difference of composition. Chemical formula? express both the different modes of arrangement, so far as these are known, and the quantitative variations which accompany those of quality. Modern chemistry, even with the aid of the most careful analysis, cannot fix the composi- tion of an organic body with certainty, unless a quantitative relation be known between it and another body, the formula of which is ascertained beyond a doubt. It was only in this way that chemists were able to fix the formulae of oil of bitter almonds, and of oil of potato spirit ; and when simple observation does not disclose a relation between two bodies, the chemist is compelled, by experiments, to create, if possible, such relations. He endeavours to resolve one of the bodies into two or more products ; he examines the products obtained by the action of oxygen, or of chlorine, of alkalies or of acids, and thus he at last succeeds in obtaining one or more products, the composition of which is known, and their formulae discovered. He now connects the formulas of the body under examination with those of CHEMICAL FORMULA. 335 the known products obtained from it. He makes out the sum of the whole from a knowledge of one, several, or all the parts of which that whole consists, or into which it may be resolved. Thus the absolute number of equivalents of carbon, hydrogen, and oxygen, in a molecule of sugar, cannot be fixed by the analysis of the sugar. The dexterity of a chemist gives us no proof of the accuracy of his analysis of salicine or amygdaline ; but sugar combines with oxide of lead ; it is resolved by fermentation into carbonic acid and alcohol, two compounds, the formulae of which are accurately known. Amygdaline is resolved into hydrocyanic acid, oil of bitter almonds, and sugar ; salicine yields sugar and saligenine. It is plain that when the weight of the body, and that of one, two, or all of the products derived from it, as well as their formulae, are known, the number and proportion of one, of two, or of all its elements in other words, its formulae may be deduced. The result of -analysis may thus be confirmed or corrected. The significance of chemical formulae will now be obvious. The true formula of a substance expresses the quantitative relations in which the body stands to one, two, or more others. The formula of sugar expresses the sum of all its elements, which combine with an equivalent of oxide of lead ; and it also represents the sum of the weights of car- bonic acid and alcohol, into which it is resolved by fermenta- tion. We now see why the chemist is often compelled to split up into numerous products the substances whose com- position he wishes to determine ; and why, also, he studies its compounds with other bodies. These things all serve to control his analysis. No formula deserves entire confidence when the body, the composition of which it proposes to represent, has not been thus examined.* * Let us illustrate this by the example of sugar. The analysis of sugar, often repeated, indicates that it contains for every equivalent of carbon, one equivalent of hydrogen, and one of oxygen. But this analysis, how- ever accurate, only tells us the relative properties of these elements, not their absolute amount in an equivalent of sugar. It cannot tell us what is the equivalent of sugar. We cannot say whether the true formula of 336 LETTERS ON CHEMISTRY. Some modern physiologists, forgetting that the knowledge of the mutual relations of two phenomena must precede their correct expression in numbers, have employed chemical formulae in such a manner that their use degenerated into sugar be C H 0, C 2 H 2 2 , C, H 4 4 , C 6 H 6 6 , C 9 H 9 9 , C 12 H 12 12 , or any other multiple of C H 0. To ascertain this, we first study its com- binations, and we find that sugar combines with oxide of lead. The com- pound, being analysed, is found to contain, for one equivalent of oxide of lead, represented by the number 103 '7, a weight of sugar represented by the number 180, a number much exceeding that of the weight of the oxide of lead. If we compare this number with those indicated by the supposed formulae above given, among which we could not before fix on the right one, we found that these formulae (C=6, H = l, = 8), yield respectively the numbers 15, 30, 60, 90, 120, and 180. Assuming, therefore, the compound of sugar with oxide of lead to consist of one equivalent of each, it is manifest that the last formula, C 12 H ]2 12 z= 180, is the right one. We next proceed to study the products of the decomposition of sugar ; and we find that, in fermentation, it yields no other products than alcohol and carbonic acid, the formulae of which are known. That of alcohol is C 4 H 6 2 ; that of carbonic acid is C 2 . And, if we attend to the quantities of these products yielded by 180 pai*ts of sugar, or one supposed equivalent, we find that 180 grains of sugar yield 92 grains of alcohol and 88 grains of carbonic acid. Now the equivalent of carbonic acid, C 2 is 22; 88 grains of the acid, therefore, correspond to 4 equivalents. In like manner, the equivalent of alcohol, C 4 H 6 2 , is 46 ; so that 92 grains correspond to two equivalents of alcohol. We have found, there- fore, that if the formula of sugar be supposed to be C 12 H 12 0, 2 , 1 equiva- lent of sugar yields 2 equivalents of alcohol, and 4 of carbonic acid ; and if we add the formulae in that proportion, the sum gives the formula of sugar. Alcohol. Carbonic acid. 2 (C, H 6 0.) = C 8 H 12 4 4 C 2 = C, 8 2 eq. alcohol. 4 eq. carbonic acid. 1 eq. sugar. C 8 H 12 4 +C 4 8 = C 12 H 12 12 Our formula, as deduced from the composition of the compound of sugar with oxide of lead, is therefore confirmed by the study of the products of its decomposition by fermentation . There is still, however, another view possible. Sugar may have the formula C 6 H fl O a ; and in that case, the compound with oxide of lead must contain 2 equivalents of sugar to 1 equivalent of oxide of lead, whereas we assumed it to contain 1 equivalent of sugar. In like manner, 1 equivalent of sugar, C 6 H 6 6 , will yield, on fermentation, 1 equivalent of alcohol, ' and 2 equivalents of carbonic acid. To decide this point, we have again recourse to the study of the products of decomposition of sugar. We find, that when exposed to a certain heat, especially in contact with bases, it loses a certain amount of water, and what may be called anhydrous sugar is left. Let us suppose, that sugar is so treated, and that 180 parts lose 27 of water, leaving 153 parts of anhydrous sugar combined with the base employed, from which it may be CHEMICAL FORMULA. 337 mere meaningless play with numbers in their hands. Instead of searching for the expression of a relation actually existing and manifested in the phenomena, they endeavoured to exhibit by numbers relations which did not exist in nature, and had never been observed. But this power does not in reality belong to numbers. separated and again caused to take up the 27 parts of water it had lost, it is obvious, that in this case, the formula of the anhydrous sugar will be C 12 H 9 9 ; whereas, if we call sugar C a H 6 6 , the anhydrous sugar will be C e H 4 * O 4 $, an impossible formula. We are, therefore, compelled to adopt the formula with 12 equivalents of carbon at least ; there may be possibly, 24 or 48 ; but there cannot be less than 12. If we were to adopt the formula C 4 H 4 4 , this would not agree with the results of fer- mentation, nor would C 8 H 8 8 . And we have no reason to go higher than C 12 H 12 12 , which suffices to explain all the facts observed. We conclude, from this last experiment, that sugar is thus constituted : C 12 H 9 9 + 3 H0= C 12 H 12 12 ; that is, one equivalent of anhydrous sugar, and 3 equivalents of water." This illustration is not given as an absolutely exact account of what takes place ; for crystallised cane-sugar is C 12 H u O u = C 12 H 9 9 + 2 HO ; and in fermentation it takes up 1 equivalent of water, forming dry grape-sugar ; C 12 H n O u + HO =r C 12 H 12 12 . Crystallised grape-sugar is C 12 H 14 14 ; and in fermentation it loses 2 equivalents of water ; C 12 H 14 14 2 HO =C 12 H 12 ]2 . But, to avoid confusion, I have assumed H 12 12> (W. G.) LETTERS ON CHEMISTRY. LETTER XXYI. Nutritive Substances strictly so called Respiratory food The Oxygen absorbed in the lungs is entirely given out in combination with Carbon and Hydrogen Amount of Carbon daily consumed by an adult- Amount of Oxygen required to convert it into Carbonic Acid Respiration. THE discoveries of chemistry in the domain of physiology have in recent times given us unexpected information in regard to many of the most important processes in the animal organism, and have led us to clearer views concerning those things to which the names of poisons, food, or remedial agents must be applied. The notions of hunger and of death are no longer confined to a mere description of symptoms. It is now ascertained, with positive certainty, that all the substances which constitute the food of man must be divided into two great classes, one of which serves for the true nutrition and reproduction of the solid parts of the animal body, whilst the other ministers both to the performance of these processes, and also to quite different purposes. We can prove, with mathematical certainty, that as much flour or meal as can lie on the point of a table-knife is more nutritious than five mass (about nine quarts) of the best Bavarian beer ; that a person who is able daily to consume that amount of beer, obtains from it, in a whole year, in the most favourable case, exactly the amount of nutritive constituents which is contained in a five pounds loaf of bread, or in three pounds of flesh. TOae entire subversion of all our former notions concerning the share taken by beer, sugar, starch, &c., in the vital process, gives to a more intimate knowledge of the recent researches, and the consequently prevalent views on this subject, a certain degree of interest. OXYGEN CONSUMED IN A YEAR. 339 The primary conditions of the maintenance of animal life are, a constant supply of food that is, the stilling of hunger and of oxygen, in the shape of atmospheric air that is, the process of respiration. During every moment of life, oxygen is absorbed from the atmosphere in the organs of respiration ; and the act of breathing cannot cease while life continues. The observations of physiologists have demonstrated that the body of an adult man sufficiently supplied with food, neither increases nor diminishes in weight during twenty-four hours, and yet the quantity of oxygen absorbed into his system in that period is very considerable. According to the experiments of Lavoisier and of Menzies, an adult man takes into his system from the atmosphere, in one year, no less than seven hundred to eight hundred pounds weight of oxygen ; and yet we find his weight at the end of the year either exactly the same, or differing one way or other by, at most, a few pounds. What, it may be asked, has become of the enormous amount of oxygen thus introduced into the human system in the course of one year ? We can answer this question satisfactorily. No part of the oxygen remains in the body, but it is given out again, combined with carbon and hydrogen. The carbon and hydrogen of certain parts of the animal body have combined with the oxygen introduced through the lungs and skin, and have passed off in the forms of carbonic acid and vapour of water. At every expiration and every moment of life, a certain amount of its elements are separated from the animal organism, having entered into combination with the oxygen of the atmosphere, in the body itself. In order to obtain a basis for an approximate calculation, we may assume, that in an adult man, the weight of the whole mass of the blood is 1 2 pounds,* of which 80 per cent. * This estimate of the quantity of blood circulating in the human body is given on the authority of Bischoff, on a calculation founded on Welcker's method. This consists in first taking a sample of the normal blood of the body to be examined, and then mincing the organs of the whole body, washing them with water, and adding to this watery extract the remainder z 2 340 LETTERS ON CHEMISTRY. is water. Now, from the known composition of the blood, we know that in order to convert its whole amount of carbon and hydrogen into carbonic acid and water, there is required a quantity of oxygen, which is taken into the system of an adult man in four or five days. Whether the oxygen enters into combination directly with the elements of the blood, or with the carbon and hydrogen of other parts of the body, it follows inevitably the weight of the body remaining unchanged and in a normal condition that as much of these elements as will suffice to supply with them twenty-four pounds of blood, must be taken into the system in four or five days ; and this necessary amount is furnished by the food. We have not, however, remained satisfied with mere approximation : we have determined accurately, in certain cases, the quantity of carbon taken daily in the food, and of that which passes out of the body in the fseces and urine uncombined with oxygen ; and from these investigations it appears that an adult man, taking moderate exercise, consumes 13-, 9 ff ounces of carbon, which pass off through the skin and lungs as carbonic acid gas.* of the blood. By measuring the whole of the fluid thus obtained, and diluting the sample of the normal blood previously taken, till it has gained exactly the same colour as the fluid of the maceration, the quantity of blood containtd in the latter can then be calculated from the quantity of water required to bring the sample to the same colour. Examined in this way, Bischoff estimated the weight of the whole blood in circulation in the human body to be about ^5 of the weight of the body. By the same method Welcker has found that the quantity of blood in circulation iu different animals was also about - 3 of the weight of the whole body. Valentin calculates the quantity in man at 1 ; and Weber and Lehmann at i of the weiglit of the body. Bischoif's calculation is in all probability too low. The convict executed at Munich, on whose body he operated, had suffered from scorhutus for some weeks previous to his death, and the blood appeared diseased. If we take the average weight of man to be 140 Ibs., the different estimates of the blood in the body would be 11, 18, 281bs. "Wi isberg collected 26| Ibs. from a beheaded woman, and saw 28 Ibs. 11 oz. lost by uterine haemorrhage. (J. B ) * The numbers just given are the average of the consumption of 856 soldiers in Inrraoks, whose food bread, potatoes, flesh, pease, len.tils, beans, even butter, salt, and pepper was, for a month, most accurately weighed, and each article subjected to elementary analysis. Three guards- men, who had, besides the daily allowance of '2 Ibs. of bread, an addition of 2ilbs. for each period of payment, and a drummer, who had a like FOOD AND RESPIRATION. 341 It requires 37 ounces of oxygen to convert 13 T 9 Q of carbon into carbonic acid. Again ; according to the analysis of Boussingault (Annales de China, et de Phys., Ixx. i. p. 136), a horse consumes 79-^ ounces of carbon in twenty-four hours ; a milen cow 7 Of ounces ; a pig, fed with potatoes, 21^ ounces. So that the horse requires 13 pounds 3^ ounces ; the cow 11 pounds lOf ounces ; and the pig about 3^ pounds, of oxygen,* to convert the carbon into carbonic acid. As no part of the oxygen taken into the system of an animal is given off in any other form than combined with carbon or hydrogen, and as in a normal condition, or state of health, the carbon and hydrogen so given off are replaced by those elements in the food, it is evident that the amount of nourishment required by an animal for its support must be in a direct ratio with the quantity of oxygen taken into its system. Two animals which in equal times take up by means of the lungs and skin unequal quantities of oxygen, consume an amount of the same food unequal in the same ratio. The consumption of oxygen in a given time may be expressed by the number of respirations ; it is, therefore, obvious that in the same animal the quantity of nourishment required must vary with the force and number of respirations. A child breathes quicker than an adult, and, consequently, requires food more frequently and proportionably in larger quantity, and bears hunger less easily. A bird deprived of food dies on the third day, while a serpent, confined under a bell-glass, respires so slowly that the quantity of carbonic acid generated in an allowance, were exceptions to the average. In this calculation is not in- cluded the carbon of the fresh vegetables, or sour crout, nor that of the portion of food taken by the men in the evening. According to the estimation of a serjeant, each man daily consumes, on an average, 3 oz. of sausages, |oz. of butter, I pint of beer, and ^g of a pint of brandy ; the carbon of which is more than double that of the faeces and the urine together. The faeces, on an average, amount daily to 5~oz. ; they contain 75 per cent, of water, and the dry residue contains 45*24 per cent, of carbon, and 13 '15 per cent, of ash. 100 parts of fresh faeces contain, therefore, 11 '31 of carbon, very nearly the same as an equal weight of flesh. In the above calculation, the carbon of the faeces and urine has been assumed as equal to that of the green vegetables and of those articles which are con- sumed in the evening at the public-house. * 17 ounces=i kilogramme. 342 LETTERS ON CHEMISTRY. hour can scarcely be observed, and it will live three months, or longer, without food. The number of respirations is fewer in a state of rest than during labour or exercise : the quantity of food necessary in both cases must be in the same ratio. An excess of food, and a want of a due amount of respired oxygen, or of exercise, as also great exercise (which obliges us to take an increased supply of food), and weak organs of digestion, are incompatible with one another. But the quantity of oxygen received by an animal through the lungs not only depends upon the number of respirations, but also upon the size and expansion of the lungs, and the rapidity of the circulation. The number of pulsations in a given time gives a tolerably accurate measure of the velocity of the current of blood through the lungs, although it cannot tell us the exact quantity of the blood flowing to them, which depends on the interior size of the cavities of the heart. All these things exert a decided influence on the consumption of oxygen, and consequently on the amount of food required. Two persons, or two animals, with a different number of pul- sations or a different volume of lungs, consume, in like cir- cumstances, a different amount of food ; he who has the smaller lungs consuming less. If both consume the same amount of food, it may happen that one remains thin, while the other becomes fat. The right appreciation of the size of the chest gives to the experienced agriculturist a secure means of judging of the milking qualities of two cows, or of the fattening qualities of two oxen or pigs, otherwise similar. In summer the air is not only warmer and less dense, and consequently contains less oxygen than colder air, but it contains aqueous vapour ; in winter it is nearly dry. The space occupied by the vapour in the warm air is, in winter, filled by air ; that is to say, an equal volume of air in frosty weather contains more oxygen than in summer. In like manner, the absolute quantity of oxygen in the inspired volume of air varies with the height of the baro- meter. At the level of the sea a cubic foot of air contains more oxygen than the same volume of air does on high RESPIRATION AND ANIMAL HEAT. 343 mountains. In the inhabited elevated plateaus of Central America, at the height of 8000 to 10,000 feet, the air con- tains in an equal volume nearly one-third less oxygen than in the deep shafts of the Cornish tin mines. But these variations in the density of the air from temperature, evapo- ration, or pressure, exert no perceptible influence on the quantity of oxygen taken up by the blood in every second of time, and therefore have no notable effect on the daily amount of food required. The consumption of oxygen is entirely dependent on the respiratory motions and on the circulation of the blood ; and this explains the influence of the exhausting heat of tropical climates, and the greater consumption of oxygen in cold air j the former diminishing, and the latter increasing, the number and depth of the respirations. The mutual chemical action of the constituents of the food and of the oxygen conveyed by the circulation to all parts of the body is the source of animal heat. 344 LETTERS ON CHEMISTRY. jj I it it Alt i L r NIVKK*ITY OK :. i ALIFOUNIA. LETTER XXVII. Animal Heat derived from the Oxidation of Carbon and Hydrogen in the Body The Food is Burned in the Body, as Fuel in a Furnace Effects of External Cooling on the amount of Food required to keep up the Heat of the Body A Starving Man soon yields to Cold Clothing com- pensates to a certain extent for Food Effects of Starvation ; the Body rapidly Oxidised and Consumed Analogous Phenomena in Disease The Solid and Liquid Excreta are not Putrescent, but partially Oxidised, and Represent the Soot, Smoke, and Ashes of a Furnace Compensating Action of Organs ; Kidneys and Intestines ; Lungs and Liver Respi- ration is the Moving Spring. THE source of animal heat, its laws, and the influence it exerts upon the functions of the animal body, constitute a curious and highly interesting subject, to which I would now direct your attention. All living creatures, whose existence depends upon the absorption of oxygen, possess within themselves a source of heat, independent of surrounding objects. This general truth applies to all animals, and extends to the seed of plants in the act of germination, to flower-buds when developing, and fruits during their maturation. In the animal body, heat is produced only in those parts to which arterial blood, and with it the oxygen absorbed- in respiration, is conveyed. Hair, wool, and feathers, receive no arterial blood, and therefore in them no heat is developed. The combination of a combustible substance with oxygen is, under all circumstances, the only source of animal heat. In whatever way carbon may combine with oxygen, the act of combination is accompanied by the disengagement of heat. It is indifferent whether this combination takes place rapidly or slowly, at a high or at a low temperature : the amount of heat liberated is a constant quantity. The carbon of the food, being converted into carbonic acid ANIMAL HEAT. 345 within the body, must give out exactly as much heat as if it had been directly burned in oxygen gas or in common air ; the only difference is, the production of the heat is diffused over unequal times. In oxygen gas the combustion of carbon is rapid and the heat intense ; in atmospheric air it burns slower and for a longer time, the temperature being lower. It is obvious that the amount of heat liberated must increase or diminish with the quantity of oxygen introduced in equal times by respiration. Those animals, therefore, which respire frequently, and consequently consume much oxygen, possess a higher temperature than others, which, with a body of equal size to be heated, take into the system less oxygen. The temperature of a child (102 F.) is higher than that of an adult (99 -5 F.). That of birds (104 to 1054 F.) is higher than that of quadrupeds (98'5 to 100 '4 F.) or than that of fishes or amphibia, whose proper temperature is from 27 to 3 '6 F. higher than that of the medium in which they live. All animals, strictly speaking, are warm-blooded ; but in those only which possess lungs is the temperature of the body quite independent of the sur- rounding medium. The most trustworthy observations prove that in all climates, in the temperate zones as well as at the equator or the poles, the temperature of the body in man, and in what are commonly called warm-blooded animals, is invariably the same ; yet how different are the circumstances under which they live ! The animal body is a heated mass, which bears the same relation to surrounding objects as any other heated mass. It receives heat when the surrounding objects are hotter, it loses heat when they are colder, than itself. We know that the rapidity of cooling increases with the difference between the temperature of the heated body and that of the surrounding medium; that is, the colder the surrounding medium the shorter the time required for the cooling of the heated body. How unequal, then, must be the loss of heat in a man at 346 LETTERS ON CHEMISTRY. Palermo, where the external temperature is nearly equal to that of the body, and in the polar regions, where the exter- nal temperature is from 104 to 122 F. lower ! Yet, notwithstanding this extremely unequal loss of heat, experience has shown that the blood of the inhabitant of the arctic circle has a temperature as high as that of the native of the south, who lives in so different a medium. This fact, when its true significance is perceived, proves that the heat given off to the surrounding medium is restored within the body with great rapidity. This com- pensation must consequently take place more rapidly in winter than in summer, at the pole than at the equator. Now, in different climates the quantity of oxygen intro- duced into the system by respiration, as has been already shown, varies according to the temperature of the external air ; the quantity of inspired oxygen increases with the loss of heat by external cooling, and the quantity of carbon or hydrogen necessary to combine with this oxygen must be in- creased in the same ratio. It is evident that the supply of the heat lost by cooling is effected by the mutual action of the elements of the food and the inspired oxygen, which combine together. To make use of a familiar, but not on that account a less just illustra- tion, the animal body acts, in this respect, as a furnace, which we supply with fuel. It signifies nothing what interme- diate forms food may assume, what changes it may undergo in the body ; the last change is uniformly the conversion of its carbon into carbonic acid, and of its hydrogen into water. The unassimilated nitrogen of the food, along with the unburned or unoxidised carbon, is expelled in the urine or in the solid excrements. In order to keep up in the furnace a constant temperature, we must vary the supply of fuel according to the external temperature. In the animal body the food is the fuel ; with a proper supply of oxygen we obtain the heat given out during the oxidation or combustion of that fuel. In winter, when We take exercise in a cold atmosphere, and when consequently the amount of inspired oxygen increases, the necessity for CARBON" OF FOOD AND OXYGEN INSPIRED. 347 food containing carbon and hydrogen increases in the same ratio ; and by gratifying the appetite thus excited, we obtain the most efficient protection against the most piercing cold. The oxygen taken into the system is given out again in the same form, both in summer and winter : we expire more carbon at a low than at a high temperature, and require more or less carbon in our food in the same proportion \ and, consequently, more is respired in Sweden than in Sicily, and in our own country an eighth more in winter than in summer. Even if an equal weight of food is consumed in hot and cold climates, Infinite Wisdom has ordained that very unequal proportions of carbon shall be taken in it. The fruits used by the inhabitants of southern climes do not contain, in a fresh state, more than 12 per cent, of car- bon, while the blubber and train oil which feed the inhabitants of polar regions contain 66 to 80 percent, of that element. From the same cause it is comparatively easy to be tem- perate in warm climates, or to bear hunger for a long time under the equator ; but cold and hunger united very soon produce exhaustion. A starving man is soon frozen to death. The animals of prey in the arctic regions, as every one knows, far exceed in voracity those of the torrid zone. In cold and temperate climates, the air, which incessantly strives to consume the body, urges man to laborious efforts, in order to furnish the means of resistance to its action, while in hot climates, the necessity of labour to provide food is far less urgent. Our clothing is merely an equivalent for a certain amount of food. The more warmly we are clothed the less urgent becomes the appetite for food, because the loss of heat by cooling, and consequently the amount of heat to be supplied by the food, is diminished. If we were to go naked, like certain savage tribes, or if in hunting or fishing we were exposed to the same degree of cold as the Samoyedes, we should be able with ease to consume half of a calf, and perhaps a dozen of tallow candles 348 LETTERS ON CHEMISTRY. into the bargain, daily, as warmly clad travellers have related with astonishment of these people. We should then also be able to take the same quantity of brandy or train oil without bad effects, because the carbon and hydrogen of these substances would only suffice to keep up the equi- librium between the external temperature and that of our bodies. According to the preceding expositions, the quantity of food is regulated by the number of respirations, by the temperature of the air, and by the amount of heat given off to the surrounding medium. No isolated fact, apparently opposed to this statement, can aifect the truth of this natural law. The cooling of the body, by whatever cause it may be produced, increases the amount of food necessary. The mere exposure to the open air, in a carriage, or on the deck of a ship, by increasing radiation and vaporisation, increases the loss of heat, and compels us to eat more than usual. The same is true of those who are accustomed to drink large quantities of cold water, which is given off at the tem- perature of the body, 9 8 -5 F. It increases the appetite, and persons of weak constitution find it necessary, by con- tinued exercise, to supply to the system the oxygen required to restore the heat abstracted by the cold water. Loud and long continued speaking and singing, the crying of infants, moist air, all exert a decided and appreciable influence on the amount of food which is taken. The unequal loss of heat in summer and winter, in cold and hot climates, is not the only cause which renders neces- sary unequal quantities of food. There are other causes, which exert a very decided influence on the amount of food required. To these causes belong bodily exercise, and all kinds of bodily labours and exertion. The consumption of mechanical force in the body is always equal to a waste of matter in the body, and this must be restored in the food. When a man or an animal works, a certain amount of food must be added ; increased work and effort without a corresponding increase PHENOMENA OF STARVATION. 349 of food, cannot be continued for any length of time ; the health of the man or animal soon gives way. But the waste of matter or the force exerted always stands in a certain relation to the consumption of oxygen in respiration ; and the quantity of oxygen taken up in a given time determines, in all seasons, and in all climates, the amount of food necessary to restore the equilibrium. While the labourer, in winter, with equal consumption of force and of oxygen, is compelled to obviate the loss of heat by warm clothing (bad conductors of heat), in summer he is bathed in perspiration. If the amount of food and that of oxygen, be equal in summer and in winter, the develop- ment of heat is also equal. The whole process of respiration appears most clearly developed, when we consider the state of a man, or other animal, totally deprived of food. The respirations are unchanged ; oxygen, as before, is taken up from the air, and carbonic acid and water are given off. We know with certainty whence the carbon and hydrogen are derived, for as the starvation continues, we see the carbon and hydrogen of the body diminishing. The first effect of starvation is the disappearance of fat, and this fat cannot be traced either in the urine or in the scanty faeces. Its carbon and hydrogen have been given off through the skin and lungs, in the form of oxidised pro- ducts ; it is obvious that they have served to support respiration. In the case of a starving man, 32^ oz. of oxygen enter the system daily, and are given out again in combination with a part of his body. Currie mentions the case of an individual who was unable to swallow, and whose body lost 100 Ibs. in weight during a month ; and according to Martell (Trans. Linn. Soc., vol. xi. p. 411), a fat pig, overwhelmed in a slip of earth, lived 160 days without food, and was found to have diminished in weight, in that time, more than 120 Ibs. The whole history of hybernating animals, and the well-established facts of the periodical accumulation, in various animals, of fat, which, at other periods, entirely 350 LETTERS ON CHEMISTRY. disappears, prove that the oxygen, in the respiratory process, makes a selection among the substances which are capable of entering into combination with it. It combines first and chiefly with those substances which have the greatest attraction for it. In the progress of starvation, however, it is not only the fat which disappears, but also, by degrees, all such of the solids as are capable of being dissolved. In the wasted bodies of those who have suffered starvation, the muscles are shrunk and unnaturally soft, and have lost their con- tractility ; all those parts of the body which were capable of entering into the state of motion, have served to protect the remainder of the frame from the destructive influence of the atmosphere. Towards the end, the particles of the brain begin to undergo the process of oxidation, and delirium, mania, and death close the scene ; that is to say, all resist- ance to the oxidising power of the atmospheric oxygen ceases, and the chemical process of eremacausis, or decay, commences, in which every part of the body, the bones excepted, enters into combination with oxygen. The time which is required to cause death by starvation depends on the amount of fat in the body, on the degree of exercise, as in labour or exertion of any kind, on the tem- perature of the air, and finally, on the presence or absence of water. Through the skin and lungs there escapes a certain quantity of water, and as the presence of water is essential to the continuance of the vital motions, its dissipation hastens death. Cases have occurred, in which a full supply of water being accessible to the sufferer, death has not occurred till after the lapse of twenty days. In one case, life was sustained in this way for the period of sixty days. . In most chronic diseases death is produced by the same cause, namely, the chemical . action of the atmosphere. When those substances are wanting, whose function in the organism is to support the process of respiration ; when the diseased organs are incapable of performing their proper function of producing these substances ; when they have lost the power of transforming the food into that shape in CAUSE OF DEATH IN CHRONIC DISEASES. 351 which it may, by entering into combination with the oxygen of the air, protect the system from its influence ; then, the substance of the organs themselves, the fat of the body, the substance of the muscles, the nerves, and the brain, are unavoidably consumed. The true external cause of death in these cases is the respiratory process, that is, the action of the atmosphere. A deficiency of food, and a want of power to convert the food into a part of the organism, are both, equally, a want of resistance : and this is the negative cause of the cessation of the vital process. The flame is extinguished, because the oil is consumed ; and it is the oxygen of the air which has consumed it. In many diseases substances are produced which are incapable of assimilation. By the mere deprivation of food, these substances are removed from the body without leaving a trace behind ; their elements have entered into combination with the oxygen of the air. From the first moment that the function of the lungs or of the skin is interrupted or disturbed, compounds, rich in carbon, appear in the urine, which acquires a brown colour. Many, perhaps most, chronic diseases in man, are caused by a misproportion, or a disturbed relation of equilibrium in the operations of the digestive and excretory organs, considered with reference to the lungs. Retaining the familiar illustration of the furnace, every one knows that the accumulation of soot in the chimney, or the throwing on of an excess of fuel, interrupts the functions of the fire- place ; that these causes act as would a stoppage of the grate below, through which the air has access. In the machine of the body, so infinitely perfect, there is a thoroughly equal relation of mutual dependence between the lungs, the intestinal canal, and the kidneys. Experienced and well-informed physicians have long known that the kidneys and intestines are the regulators of the respiratory process. The lower intestine is an organ of secretion ; it is the chimney of the organism. The foetid 352 LETTERS ON CHEMISTRY. constituents of the excreta are the soot, separated from the blood by this intestine ; while the urine contains those con- stituents of the smoke, so to speak, which are soluble in water or in alkaline or acid liquids. The notion that the solid excreta consist of putrescent matters, and that their fetor depends on this, is quite erroneous. Experiments on this point have proved that the solid excreta of the cow, horse, and sheep, and of healthy men, are not putrescent. No putrescent substance has a smell similar to that of these excreta ; and all these foetid products may be arti- ficially produced, in all their nauseous peculiarities, by pro- cesses of partial oxidation applied to albumen, fibrine, &c. The urine of the horse and cow, moreover, contains a sub- stance in considerable quantity, which, when acted on by acids, yields a pitchy matter, quite similar in its aspect to tar, and, as the most remarkable product, carbolic acid, or hydrated oxide of phenyle, the chief ingredient of common wood tar and of creosote. By the simultaneous and harmonious co-operation of the chief organs of secretion, the blood is kept in the state of composition and of purity fit for the nutritive process. Excess in eating, so much indulged in in every country, is an overloading of the grate with fuel. In the bodies of per- fectly healthy persons, a slight excess of matters which pass from the stomach into the blood, produces, nevertheless, no disturbance of the vital functions ; because that part of them which in a given time is not consumed in respiration, is sent out of the body more or less altered through the intestines or the kidneys. These organs mutually aid each other in the process. When, as the result of an overloading of the blood with combustible matter, and a consequent deficiency of oxygen, the urine, from excess of unoxidised organic matters (in the form of uric acid, &c.), is dark- coloured and turbid, this is generally a sign of deficient activity of the intestine ; and in this case, a simple purga- tive, by the action of which the unoxidised matters are removed from the blood, generally restores the disturbed equilibrium between this fluid and the inspired oxygen ; MUTUAL RELATION OF ORGANS. 353 the urine becomes transparent as usual, and recovers its natural colour. (Prout.) The lung is in itself passive ; the process which takes place in it is not, as in the glands and secretory organs determined by an internal, but by an external cause. In the lung is wanting the powerful activity which in other organs opposes external disturbances and removes their effects. The mere inspiration of dust (of organic or inorganic solid particles), causes organic deposits in the pulmonary tissue, which are also produced in a similar way by internal causes. Smoke and soot accumulate in the lungs or other tissues in the form of abnormal deposits in all cases where the proper action of the intestine and the kidneys is impeded or arrested by causes of disease. Between the lungs and the liver we find a similar relation of mutual dependence. In the lower orders of animals, and in the foetus, the size of the liver is in an inverse ratio to the undeveloped or imperfectly developed organs of respira- tion ; and even in the higher classes of animals, a small lung usually corresponds to a large liver, in healthy individuals. (Ticdemann.) The liver, roughly sketched, is the magazine for the matters destined for respiration : it is the workshop, in which they receive the shape and quality fitted for the production of animal heat. The liver is small, with a large well-developed lung ; the quicker and more perfectly the fuel is consumed, the less of it accumulates in the magazine for fuel, the size of which has the most definite relation to the rapidity of the consumption. Respiration is the falling weight the bent spring, which keeps the clock in motion ; the inspirations and expirations are the strokes of the pendulum which regulate it. In our ordinary time-pieces, we know with mathematical accuracy the effect produced on their rate of going, by changes in the length of the pendulum, or in the external temperature. Few, however, have a clear conception of the influence of air and temperature on the health of the human body ; and yet the research into the conditions necessary to keep it in the normal state is not more difficult than in the case of a clock. 354 LETTERS ON CHEMISTRY. LETTEE XXYIII. Effects of Respiration on the Inspired Air General and Pulmonary Cir- culation Composition of Expired Air Grases absorbed and given out by the Blood Process of Respiration True Cause of Death from breath- ing Expired Air Importance of Ventilation Quick-lime may be used as a Substitute One-tenth to One-fourth of the Inspired Oxygen com- bines with Hydrogen The calculated amount of Heat from the com- bustion of the known weight of Carbon, and Hydrogen, out of the Body, agrees closely with that obtained by their Oxidation in the Body. THE changes which the air undergoes in respiration have been examined with great care in recent times, and a know- ledge of the results obtained is of importance to the preser- vation of health. The lungs, as the scene of the respiratory process, consist of an arborescent ramification of tubes which become con- tinually smaller, the last twigs of which end in minute sacs or bladders, called air-cells, and communicate by the bronchi and trachea with the cavities of the mouth and nose. The walls of the air-cells are penetrated by a close net-work of very minute blood-vessels, so that the air in the cells is only separated from the blood by a membrane excessively thin, and with the blood in these vessels the air comes into imme- diate contact through the fluid which, proceeding from the blood, moistens the walls of the blood vessels. The small vessels gradually unite to form larger twigs and branches, which pour their contents into the heart through a few large trunks. The heart is divided by a partition into a right and a left half, each of which has -again an auricle and a ventricle, communicating by an opening provided with valves. The contraction of the heart is the primary cause of the motion of the blood. By the contraction of the right ventricle, the blood from the right auricle and the veins which flow into it, is forced through the so-called pulmonary arteries into the PULMONARY CIRCULATION". 355 lungs, and returns from the lungs through the so-called pul- monary veins to the left auricle and ventricle, from which last, by its contraction, it is forced through the great arterial trunk, or aorta, into the ramifications of the arterial system throughout the body. By the veins it returns as venous blood to the right auricle, and from that it passes to the right ventricle, to recommence the circulation, which lasts as long as life continues. The contraction of the heart pro- duces the beating of that organ and the pulsation of the arteries. With every stroke of the heart there is sent from it through the pulmonary arteries in the adult, calculating from the capacity of the right ventricle, a quantity of blood, estimated by physiologists at five or six ounces (Volkmann) ; and consequently there flows through the lungs in one minute, taking the pulsations at seventy-two, the astonish- ingly large quantity of from 22 to 27 Ibs. of blood. This is double the whole quantity of blood which the human body contains.* While the blood flows through the pulmonary vessels with so great a velocity, the air in the air-cells is continually changed by the respiratory motions. In health, and in a state of rest, there are fifteen or sixteen respirations per minute \ in a state of moderate exertion, twenty in the same time. With more violent motion, the strength and fulness, as well as the rapidity of the respirations increase. The quantity of expired air differs according to the size of the individual and that of the pulmonary cavity ; but we may assume that an adult man, on an average, expires \ litre, or about 30 to 31 cubic inches of air ; while, with strong and deep respiration, this quantity may be increased to about 60 cubic inches. The human lungs retain, in ordinary respiration, six to eight times as much air in the cells as is changed in each respiration. The fresh air inspired mixes with the air in the cells ; at each expiration a part of this is expelled, and its volume replaced by an equal bulk of fresh air. * See note, page 339, for the various estimates of the quantity of blood circulating in the human body. A A 2 356 LETTERS ON CHEMISTRY. In the minute net- work of vessels in the lungs, an immense surface of venous blood, therefore, comes in contact through the walls of the air-cells with the inspired air. The blood, in these circumstances, instantly undergoes a very marked alteration ; the dark, nearly black red colour of venous blood, changes into the bright red of arterial blood ; and the con- tinuance of the vital functions and of life is most intimately connected with the new properties which the blood acquires, along with the change of colour produced by contact with the air. Simultaneously with the change of colour in the blood, the air undergoes an essential change in its composition ; and to this we shall now turn our attention. The chief constituents of atmospherical air are oxygen, nitrogen, a small quantity of carbonic acid, and of ammonia, and, besides these, mere traces of combustible gases. The air always contains moisture or aqueous vapour in very variable proportion. The means employed by chemists to determine the quan- tity of the constituents of air are extremely simple. Hydrated potash, or caustic potash, absorbs more than 100 times its volume of carbonic acid, and it is easy to see that the increase of weight in a tube, filled with potash, through which we conduct slowly a cubic foot of dry air, informs us exactly how much carbonic acid this cubic foot of air con- tained. Just as carbonic acid is absorbed by potash, oxygen is absorbed by red hot copper ; and if we cause a cubic foot of dry air, purified from carbonic acid, to pass through a red hot tube filled with copper turnings, all the oxygen remains with the copper, and the gain of weight of the tube gives exactly the amount of oxygen in this cubic foot of air, the total weight of which is also known. (Dumas.) In this way it has been ascertained that dry air, free from carbonic acid, contains in 1000 parts 231 parts of oxygen and 7&9 parts of nitrogen by weight. Since oxygen. is heavier than nitrogen, the proportions by volume are some- what different. In 100 volumes of dry air as above, there are 21 volumes of oxygen and 79 of nitrogen (or 20 -9 ANALYSIS OF EXPIRED AIR. 357 exactly of oxygen : Dumas, Brunner, Bunsen, Regnault) ; and in ordinary atmospheric air there is found, on an average, 1 volume of carbonic acid in 2000 volumes of air, or, by weight, 0'75 of carbonic acid in 1000 parts by weight of air. The expired air differs very much in composition from the atmospheric air. If we introduce into a glass tube, closed at the upper end, graduated in equal divisions, and filled with dry expired air, the lower open end being immersed in mercury, about l-40th of the volume of the air of strong solution of potash, the volume of the air instantly diminishes, the carbonic acid present being absorbed by the potash. If now we add to the potash a concentrated solution of pyrogallic acid, equal to half the volume of the potash, the mixture absorbs the oxygen as rapidly as red hot copper does. The volume again diminishes, to a great degree exactly corresponding with the amount of oxygen present ; and the residue is nitrogen. In this way it is found that 100 volumes of expired air, in ordinary normal respiration, contain from 4 "5 to 5 volumes of carbonic acid, and 16 -5 to 15 volumes of oxygen. The air first expired contains less carbonic acid ; but when respiration is very deep, it contains even more, in many cases 8*5 to 9 volumes of carbonic acid, and only 11'5 to 1 1 volumes of oxygen in 100. The amount of oxygen in pure air is therefore diminished, by its contact with the blood in the lungs, to the extent of j-th or ^th, while the carbonic acid is increased above 100 times. It is obvious that the change of venous into arterial blood, and its change of colour, depend on a separa- tion of carbonic acid gas, which mixes with the air, and an absorption of oxygen, which combines with certain consti- tuents of the blood. A certain amount of oxygen passes from the air into the blood ; and the air receives, in the place of this oxygen, a quantity of carbonic acid, the volume of which is usually somewhat smaller. According to Prout, the amount of carbonic acid in the expired air is greater, in a state of mental tranquillity and 353 LETTERS ON CHEMISTRY. of moderate exercise, and when the barometer is low. In general, the per-centage of carbonic acid diminishes when the respirations are quick, but in this case the whole amount of carbonic acid expired in a given time is much greater. According to experiments made on this point, it appears, that with 6 respirations per minute the expired air contains 5*7 per cent., with 12 respirations 4*1, with 24 respirations 3 - 3, and with 48 respirations 2-9 per cent, of carbonic acid. The entire quantity of expired carbonic acid was, for 6 respirations per minute, 11 cubic inches ; for 12, 25 '3 cubic inches ; and for 48, 44 '5 cubic inches of carbonic acid. (Vierordt.) The influence of stronger and quicker respirations on the respiratory process is thus evident. By this means there is effected, in a given time, a more effectual separation of car- bonic acid, or decarbonisation of the blood. It can hardly be doubted, that with the increase or dimi- nution of carbonic acid expired, the amount of oxygen entering the blood stands in a definite relation ; and that, consequently, the blood, in the same time in which it gives off more carbonic acid, receives more oxygen from the air. Blood, when agitated with air, takes up more than -j'^th of its own volume of oxygen, and this gas may be very nearly entirely expelled by agitation with carbonic acid gas. When blood, saturated with carbonic acid, is agitated with air, car- bonic acid is displaced, and in its stead oxygen is taken up, which, in like manner, may be again expelled by carbonic acid.* * There are two opposite views concerning the form in which the absorbed oxygen is contained in the blood. One of these considers the separability of the oxygen gas by an excess of carbonic acid gas, as a convincing proof that this oxygen is not chemically united with the blood, but is only mechanically absorbed in it. But this expression for the phenomenon is decidedly erroneous.. For while 1 000 volumes of water, agitated with air, and fully saturated therewith, absorb only 9 J volumes of oxygen and 18^ volumes of nitrogen (Gay Lussac) ; 1000 volumes of blood, according to the admirable experiments of Magnus, take up 100 to 130 volumes of oxygen, and only 17 to 33 volumes of nitrogen. It' is obvious, therefore, that the oxygen gas absorbed by the blood can only be in part mechanically absorbed in the liquid ; for the liquid in blood is water, which we know in the same circumstances absorbs 11 to 14 POWER OF BLOOD TO ABSORB OXYGEN. 359 The blood of a horse, not agitated with air, but, as it flowed from the vein, yielded to Magnus, when saturated with carbonic acid, more than T -^th of its volume of oxygen gas. In this process, the blood takes alternately the bright times less oxygen. On the contrary, we must admit, that the greater absorptive power of the blood is determined by the presence of certain constituents, which have a more powerful attraction for oxygen than water has. The degree of attraction, with which the oxygen is retained in the compound which it forms in the blood, is very small ; but this is no reason for believing that it is not chemically combined. We are able to augment the absorptive power of water for many gases, by adding to it substances which have a chemical attraction, however weak, for the gas. When, for example, we add to the water phosphate of soda, its power of absorbing carbonic acid gas increases ; and 1 per cent, of the salt causes the water to take up twice as much of the gas as pure water would have done under the ordinary pressure. A solution of green vitriol (sulphate of iron) in water takes up forty times more of the deutoxide of nitrogen or nitric acid gas than pure water. The absorbed gases are separated from both liquids in vacuo, and may also be expelled, in the former case by mere agitation with air, in the latter by agitation with carbonic acid gas. No one thinks of regarding this fact, so analogous to what is observed in the blood, as a proof that the carbonic acid in the solution of phosphate of soda, or the nitric oxide in that of green vitriol, is only mechanically absorbed and not in the form of a chemical compound, because we know, that the absorptive power of the water in these cases depends on the quantity of the dissolved salt. But if the amount of gas absorbed increases in a definite ratio with the amount of salt in the solution, it is quite certain that the absorption of the gas depends on the salt, and not on the water. There ai*e two causes on which the absorption of a gas, or the absorp- tive power of a liquid depends. One is, a pressure on the gas which is in contact with the liquid, and this cause is external. The other is a chemical attraction acting from the particles or constituents of the liquid on the gas. In all the cases, in which a gas is not chemically but only mechanically retained in a liquid, the quantity of gas absorbed depends solely on the external pressure, and increases or diminishes as the pressure is increased or diminished. In the cases adduced, when the solution of phosphate of soda is saturated with carbonic acid gas by agitation with it, (and has taken up twice as much of this gas as water would do under the ordinary pres- sure,) the absorptive power of the solution, when the pressure is doubled, does not increase in the same, but in a far smaller ratio. The saturated solution of phosphate of soda now behaves to carbonic acid under double the pressure as would water, saturated with the gas, at the ordinary pressure. The increase of absorptive power is not greater than in water, because the chemical attraction which at first increased the absorptive power does not continue to act ; but when it has produced its proper effect (the formation of a chemical compound), ceases to act further. In the same way, the solution of green vitriol, saturated with nitric oxide, under the ordinary pressure, behaves towards that gas under increased pressure as would water, saturated with it at the ordinary pressure. If 100 volumes of that solution are saturated, under the usual pressure, by 100 volumes of the 360 LETTERS ON CHEMISTRY. red colour of arterial or the dark purple red of venous blood. These facts prove that carbonic acid and oxygen gases, in their action on the blood, are opposed to each other. Car- bonic acid is expelled, and oxygen taken up in its stead, when the air contains a certain proportion of oxygen ; and on the contrary, when the air contains an excess of carbonic acid, oxygen is expelled. If both are present in a certain proportion, an equilibrium between them is established ; the blood then undergoes no change, and the venous blood is not converted into arterial. Moreover, if the quantity of oxygen that can be absorbed depend, according to a certain law, on the amount of the carbonic acid to be expelled, it is clear that the increase of the amount of oxygen in the air must be altogether with- out influence on the respiratoiy process. This remarkable fact has been satisfactorily ascertained by Regnault and Reiset in their admirable researches. They found that gas, the liquid, under a double pressure, absorbs, not 100 volumes more of the gas, but only 10 volumes, not more than water, previously saturated at the ordinary pressure, takes up under the same circumstances. The blood agrees perfectly with these liquids in its mode of action on gases. Were the oxygen in the blood only mechanically absorbed, the blood, which takes up out of air, containing as it does of oxygen, 12 per cent, of its own volume of oxygen, must take up under a pressure of two atmospheres, twice as much, under three atmospheres three times as much, and, if agitated with pure oxygen, nearly five times as much. So long as it is not proved, that the absorptive power of blood for oxygen gas does not vary with the pressure in this way, we must assume that the cause of its absorption by the blood is a chemical attraction, by the effect of which a chemical compound is formed in the blood. The experiments of Regnault and Reiset, in which animals breathed in an air much richer in oxygen than the atmosphere, and the circumstance, that at great heights, which like the great plateaux of central America are inhabited, respiration goes on, just as at the level of the sea, prove, that the amount of oxygen absorbable by the blood is a constant value, and, to a certain degree, inde- pendent of the external pressure. In the neighbourhood of the Piticaco lake, 15,000 people live in the town of Puno, at a height of 12,000 feet above the sea. The city of Potosi, in Bolivia, at a height of 12,600 feet, has 30,000 inhabitants. In these countries the people inspire only about | of the absolute quantity of oxygen which enters the lungs at each inspi- ration at the sea level, and it is evident, that if the amount of absorbed oxygen differed in the same ratio, this change must exert a marked and essential influence on the vital functions, such as could not have escaped observation. THE LUNGS NOT THE SEAT OF CARBONIC ACID. 361 animals living for twenty-two to twenty-four hours in an atmosphere containing twice or thrice as much oxygen as the air, experienced no kind of uneasiness ; and that the products of respiration, in their quantity and relative proportion, were exactly the same as when the same animals lived in common air. These experiments, as well as those of Magnus, prove that the lungs are not the true seat of the formation of carbonic acid, and are not the true source of animal heat, like a fire-place ; but that, in the arterial blood, a current of oxygen is conveyed throughout the body, which, in its passage through the minuter vessels, causes the formation of products of oxidation or combustion, among which is carbonic acid, and consequently gives rise to a disengagement of heat. The relation of dependence between the absorption of oxygen and the formation and expulsion of carbonic acid seems further to prove that both, in the blood, are conveyed and carried by the same means, namely, the blood corpuscules ; that these absorb oxygen in the lungs, and during the circulation give off that oxygen and take up the carbonic acid generated. From this it follows, that these corpuscules cannot take up more oxygen than they have given off carbonic acid, because the one gas takes the place of the other, and because the two cannot exist at one time in the same place, but mutually displace each other. It is further evident, that the amount of carbonic acid in the air is one chief obstacle to the separation of that gas from the blood, and, therefore, an obstacle to the absorption of oxygen. When the amount of carbonic acid increases, the absorption of oxygen is impeded, even when its quantity remains the same. It is only by a corresponding addition of oxygen that this injurious effect of carbonic acid can be counteracted. Such an increase of oxygen never occurs under ordinary circumstances ; but Regnault and Reiset have observed, that animals could live in air containing one and a half to twice as much oxygen as common air, even if the amount of carbonic acid were so great as from 17 to 23 per cent., that is about four hundred times greater than in 362 LETTERS ON CHEMISTRY. common air ; and this, without any injurious effect, after twenty-two to twenty-six hours. Such a proportion of carbonic acid in common air is absolutely incompatible with life. The fact, that men and animals die very rapidly from inhaling pure carbonic acid, while they live comparatively much longer in nitrogen or in hydrogen gases, is explained by this that in an atmosphere of carbonic acid the blood cannot give off any portion of that gas, but on the contrary absorbs more of it, by which the small proportion of oxygen in venous blood is expelled from the blood, and consequently its vital functions are much impeded, nay arrested. The condition most favourable to a rapid and perfect formation of arterial blood, and a more accelerated expulsion of carbonic acid from the venous blood is, consequently, a rapid change of air in the air-cells of the lungs. When the inspired air has the same composition as that which is exhaled, the object of respiration is no longer attained. The expired air is used air, which cannot a second time perform the same function in the lungs. The venous blood is no longer changed into arterial ; difficulty of breathing, and, finally, suffocation, soon come on, just as if the mouth and nose had been closed. In this case, death is determined by two causes. One is, beyond doubt, the deficiency of oxygen ; the other is the presence of carbonic acid, by the presence of which the absorption of oxygen is impeded. In one of the experiments of Regnault and Reiset, a dog, three years old, in an atmosphere, the amount of oxygen in which had fallen to 4^ per cent., while that of carbonic acid was 9| per cent., fell into death-like convulsions ; but he soon recovered 'in pure air, and in half-an-hour was as lively as before. In these experiments, the carbonic acid given out from the lungs was for the most part removed, in the confined space in which the animal breathed, by solution of potash, intro- duced along with the animal. If we reckon, in the state of rest, fifteen respirations per minute, and for each thirty-one cubic inches of air (English AIR VITIATED BY RESPIRATION". 363 measure), and in the expired air 5 per cent, of carbonic acid, and 15 per cent, of oxygen, we easily find, that a man in twenty-four hours produces 540 litres or about 19 cubic feet (English measure) of carbonic acid, consuming in the same time 10,800 litres or about 380 cubic feet of air.* In a closed space, eight feet high, nine long, and eight wide, a man could not breathe for twenty-four hours without uneasiness. At the end of that time the air would have the composition of expired air ; and if the patient remained longer in the same air, a morbid state, and, finally, death would ensue. Lavoisier and Seguin found that the carbonic acid of expired air when again inspired, may be raised to 10 per cent., but not beyond that quantity, even when respiration was continued, which it could only be for a very short time. This proportion of carbonic acid may be regarded as the limit at which life is endangered in man. Cases of this kind, in which death has been caused by the respiration of many persons in a confined space, too small for the abode of so many, are not rare. Every one has heard of the shocking results of the confinement of a number of prisoners in the Black Hole at Calcutta for one night, in the course of which most of them died. One of the most recent and lamentable accidents of this kind happened last year in an emigrant ship, in which, during a storm off the English coast, the emigrants were confined below. In less than six hours more than sixty persons perished. In a space in which many persons breathe, and in which the air is but imperfectly renewed through accidental chinks in doors and windows, the elongation of the flame of a candle, and its burning dimly, distinctly show the altered state of the air. Even the very idea of respiring air, which has sojourned for a time in the lungs of another, although of a healthy * According to experiment, these numbers may be regarded as the minima of production of carbonic acid and consumption of air. With 18 respirations per minute, the consumption of oxygen already rises by one-fifth. 364 LETTERS ON" CHEMISTRY. person, causes discomfort. It is certain that 1 per cent, of carbonic acid in the air produces a sensible uneasiness ; and the advantage of a judiciously arranged renewal of the air, or ventilation, for all apartments, in which people remain altogether, is quite obvious. For every adult there should be supplied to such an apart- ment at least 6 cubic metres, or 216 cubic feet (English) per hour, of pure air ; in general about one-half more is reckoned upon. In the air of the Chamber of Deputies, at Paris, the hall of which has the cubical extent of 5000 cubic metres, Leblanc found that when 600 persons were present, and with a ventilation of 11,000 cubic metres per hour, the air flowing out contained, notwithstanding, 1 part of carbonic acid by weight in 400, which is 2jr or 3 times more than is contained in pure air. In close places, in ships, many sick rooms and bed rooms, deficient ventilation might advantageously be compensated for by the use of hydrate of lime. The action of slaked lime depends on its great power of absorbing carbonic acid. In a room in which carbonic acid gas is present, the gas is very rapidly removed by slaked lime spread on a board. One cubic foot (Hessian, = 0-551, C. F. English) of it, which, when moist, weighs 18 or 20 Ibs., and contains two-thirds of its weight of dry lime, absorbs, in order to be converted into carbonate of lime, more than 1100 litres (70 Hessian, or 38 '8 English cubic feet) of the gas. In the small closed space formerly described, if the carbonic acid formed were removed by means of a few pounds of slaked lime from the beginning, and its injurious effects thus avoided, a man would be able to live three or four times as long as without the lime. Since such a space cannot be hermetically closed, the absorbed carbonic acid would be immediately replaced by an equal volume of fresh air, entering through the chinks. The only inconvenience from the use of lime is, that .as the lime combines with the acid, the w T ater of the hydrated lime is set free, and partly evaporates, so that the confined man or animal soon breathes an air saturated with aqueous CARBONIC ACID REMOVES MOISTURE. 365 vapour. This inconvenience is well known to those who inhabit a newly built house. It appears during the first months, very strikingly in the winter months, in the form of an excess of moisture, which condenses in drops on the windows and cold walls. This is observed in houses which have been for years exposed to the action of dry air ; and always for the first time when such houses are first inhabited. It does not proceed from ordinary moisture in the walls, but from the dry hydrate of lime in the mortar, which only gives out the twenty-four per cent, of water (which are chemically combined in it) as moisture, when the lime obtains a supply of carbonic acid to combine with it and displace the water. This supply is abundantly furnished by the lungs of those who inhabit the house. By closing the windows and burning charcoal in chauffers in the rooms of new houses, before occu- pying them, the inconvenience arising from the water of the lime is effectually cured. The continuance of life, and the preservation of health, and of a due temperature in the body of man, stands in the closest relation to the respiratory process, the full efficiency of which depends on the constant composition of the atmos- pheric air. When this is altered, by any cause, temporarily or permanently, the influence of the alteration shows itself in a transient or permanent disturbance of the vital functions. The living in low situations, in which the air is stagnant, in damp places, where carbonic acid is produced by decay, or in an air saturated with moisture at a high temperature, has long been recognised by physicians as the proximate caiise of many diseases. In sleeping rooms, where plants grow, which during the night absorb oxygen and give out carbonic acid, in close rooms, in which combustion goes on (for exam- ple of several lights),* the air acquires the composition of expired air, and the respiratory process is thus essentially endangered. * A cubic foot of coal gas consumes 2 to 2^ cubic feet of oxygen, and produces 1 to 2 cubic feet of carbonic acid. 366 LETTERS ON CHEMISTRY. It has been pointed out, that in respiration, the amount of the expired carbonic acid, by volume, is not equal to that of the inspired oxygen, but a little smaller. But when car- bon burns in a given volume of oxygen, converting it into carbonic acid, the volume of the gas undergoes no perceptible alteration. Carbonic acid contains its own volume of oxygen. If, therefore, the absorbed oxygen were employed only in producing carbonic acid, in the body, we should obtain a volume of carbonic acid equal to that of the oxygen con- sumed j whereas, the oxygen in the expired carbonic acid is rather less than the absorbed oxygen. The proportion between the two is very variable, and up to a certain point dependent on the food. With vegetable diet there is more, with a flesh diet much less oxygen exhaled in the form of carbonic acid. In the herbivora, the exhaled oxygen (as carbonic acid, the volume being the same) amounts to -f-^ or -ftj of the inspired and absorbed oxygen \ in the carnivora it is only f of the whole. In starving animals, of either class, the proportion is the same, and similar to that of animals fed 011 flesh, an evident proof, that in starvation the oxygen taken up into the blood combines, in the body, with the same substances; that is, respiration is carried on at the expense of the constituents of their bodies. The question, as to what becomes of the 10 to 25 per cent, of oxygen, which seemingly disappears in respira- tion, is easily answered, if we consider, that the only combustible elements in the body are carbon, hydrogen, and a very small amount of sulphur. It cannot be doubted, that the greater part of that deficient oxygen, is consumed in forming water, by combining with the hydrogen. The dis- appearance of the fat, a body so rich in hydrogen, in starving persons, and that of the alcohol of spirituous liquors, furnish perfect evidence of this formation of water j and the fact, that marmots or dormice, in their winter sleep, lose weight by respiration, is thereby sufficiently explained. In that state, the animal drinks no water, but yet it passes from time to time, water in its urine, the separation of which, of course, produces a loss of weight, which bears a definite rela- HEAT PRODUCED IN COMBUSTION. 867 tion to the amount of oxygen absorbed and converted into carbonic acid and water. We know exactly the amount of heat which is disengaged in the conversion of oxygen into carbonic acid and water. If we place a burning spirit-lamp under a tea-kettle filled with water, having weighed the lamp previously ; if we ex- tinguish it when the water begins to boil, that is, when every part of it has been heated to 212, and again weigh the lamp, we find how much spirit has been used, or burned, to heat the water to its boiling point. And if we know the weight of the water, and its original temperature, we can very easily calculate how many degrees of heat a certain weight of spirit gives out in combining with oxygen. With a proper apparatus, where all the heat produced is conveyed without loss to the water, it has been in this way ascertained that one ounce of pure spirit can heat 69 ounces of water from the freezing to the boiling point. Every ounce of these 69 ounces has therefore received 100 degrees (centigrade) of heat, and all together have received 69 times as much, or 6900 degrees. This number, 6900, may be taken to express the amount of heat produced by the combustion of one part by weight of spirit, and this in the form of degrees of heat gained by a known weight of water. In the same way, the heat of combustion in carbon, hydro- gen, coals, wood, and peat, &c., has been ascertained. The heat produced by coals is, on the same scale, 5625. With lib. of coals we can heat 56 J Ibs. of water from the freezing to the boiling point, or raise 562| Ibs. 10, or 5625 Ibs. 1 in temperature. The unit of heat is not an ordinary degree, but it is the amount of heat which a weight of water, equal to that of the burnt body, receives when its temperature is raised one degree of the centigrade scale. The heat of combustion of pure carbon is greater than that of coals ; according to Andrews, it is 7881 ; that of hydrogen is still higher, namely, 33,808 units of heat. By the combustion of hydrogen, water is formed ; by that of carbon, carbonic acid is produced ; and since water contains 368 LETTERS ON CHEMISTRY. eight times the weight of oxygen that it does of hydrogen, while carbonic acid contains 2^ times the weight of oxygen that it does of carbon, one part, by weight, of oxygen, in its conversion into carbonic acid, yields 2950 units of heat, and in its conversion into water 4226 units of heat. Consequently, if we know how much oxygen an animal consumes in twenty-four hours, and the quantity of carbonic acid and of water produced, the latter being known from the bulk of the oxygen which disappears as gas, it is easy to cal- culate the whole amount of heat which is produced by an animal in respiration. It is moreover easy to see that, when an animal is made to breathe in a proper apparatus, entirely surrounded with cold water, the number of degrees of heat given off by the animal in a definite time to the surrounding medium, may be easily determined. In this way it has been ascertained with certainty that the number of degrees of heat produced by an animal in the process of oxidation going on in its body, corresponds very closely to that which the same apparatus would receive, if it were heated by a fire, in which a quantity of oxygen, equal to that in the ascer- tained carbonic acid, and also to the portion of oxygen which has disappeared (as water) had been converted into the same quantities of carbonic acid and water. The question of the origin of animal heat is therefore satisfactorily solved. COMPOSITION OF BLOOD, 369 LETTEB, XXIX. Nutritious or Plastic Food The Blood ; its fibrine, globules, and albu- men Its ashes; they contain iron Importance of Albumen ; as in the Egg, it is the foundation of all the Tissues Fibrine and Albumen, Flesh and Blood, are the same in Composition Muscular Fibre, con- vertible into Albumen, even out of the Body Milk Caseine Its rela- tion to Albumen and Fibrine Nutrition of Carnivora, and of the Suckling Mammalia ; of Graminivora and Herbivora, essentially the same Composition of their Food Vegetable Albumen, Fibrine, and Caseine identical with the corresponding Animal Substances Vegetables produce the food of Animals Animals destroy this Food, and return it to the Air and Soil, as Carbonic Acid, Water, Ammonia, and Salts, to serve again as food for Plants Products of the Oxidation of Albumen, &c. Plastic, or Nitrogenous, or Sanguigenous elements of food, can alone form Tissues The Non-nitrogenous, or Respiratory elements of food, such as Fat, have not this property ; and Fat and Water in Tissues, are only mechanically absorbed. IN my last letter I endeavoured to give you some explana- tion of the functions, at once so simple and so wonderful, which oxygen performs in the animal economy. Allow me now to add some remarks on those substances which are designed to keep the mechanism of the system in action, namely the alimentary or nutritious matters. If the growth or increase of mass in the animal body, the development of its organs and their reproduction, proceed from the blood, that is, the constituent parts of the blood, only those substances can serve these purposes which con- tain the elements of blood in a form and with qualities such that they can be converted or transformed into blood. The blood contains 79 or 80 per cent, of water, and 20 or 21 of solid matter, of which lj to 1J per cent, are incom- bustible, and remain after incineration as blood ash. The clot or coagulum consists of blood corpuscules enclosed in a network of fibrine, which latter body only amounts to T 3 ^ per cent, of the entire blood. The globules or corpuscules 370 LETTERS ON CHEMISTRY. contain the colouring matter of the blood, distinguished by its never-failing and very considerable amount of iron. They contain further a substance identical with the chief solid constituent of the serum, namely albumen, which commu- nicates to the serum all the properties of white of egg. Blood, or the serum of blood, coagulates when heated. The coagulating substance is the albumen of the blood. One half of the ash of blood is sea salt. Besides this, there are found, originally in part dissolved in the serum, in part in chemical combination with the combustible constitu- ents (fibrine, albumen, by the influence of heat, and by the aid of the oxygen of the air, which has access through the porous shell, under the influence, therefore, of those conditions which accompany respiration, all the parts of the animal body, feathers, claws, fibrine, membranes, cells, blood corpuscules, the material of the blood-vessels and lymphatics, nerves and bones are developed. It is obvious that albumen is the foundation, the starting point of the whole series of peculiar tissues, which constitute those organs which are the seat of all vital IMPOETANCE OF ALBUMEN. 371 actions. The elements of these organs, now possessing form and vitality, were originally elements of albumen. They are the products of certain changes which albumen has undergone, under the influence of heat and oxygen, in living organisms. In the same way as in the egg, the albumen of the blood holds the first place in the process of formation of the foetus, to which it is conveyed from without. By its elements it takes a share in all processes, it determines growth, and also the production and renewal of all organised tissues in the young as well as in the adult frame. Albumen is a con- stituent of the brain and of the nerves ; of the liver, kidneys, spleen, pancreas, and of all glands. Everywhere throughout organised nature, where animal life is developed, we find the phenomena of life depending on the presence of albumen. The continuance of life is indissolubly connected with its presence in the blood, that is, in the nutrient fluid. In so far as the notions of formation, nutrition, or the nutritive property are inseparable from that of a substance, whose properties and composition are collected in the word albumen, only those substances are in a strict sense nutritious articles of food, which contain either albumen, or a substance capable of being converted into albumen. If we look at alimentary substances from this point of view, we obtain a knowledge of a natural law of the most admirable simplicity. The commonest observations teach us, that flesh possesses a greater nutritive power than all other kinds of food ; the chief constituent of flesh is muscular fibre, or the fibrine of muscle, which constitutes nearly 70 per cent, of the dried flesh, purified from fat. In the flesh, this muscular substance is interwoven with fine membranes, and a multi- tude of nerves are ramified through it, as well as innumerable minute vessels, filled with coloured or colourless fluids. Chemical analysis has detected the cause of the nutritive property of flesh, in a manner free from doubt, by showing that the fibrine of muscle and the albumen of blood contain 372 LETTERS ON CHEMISTRY. the same elements in the same proportion ; and that these two bodies stand to each other in the same relation as fresh albumen and coagulated albumen. In composition, fibrine is nothing more than albumen of blood solidified and in an organised form. The difference, if any, is so minute, that an analysis of the muscular fibre does not differ more from one of albumen of blood, than two analyses of the latter body do from each other (Annalen der Ch. und Pharni. LXXIII. 126). The blood, considered as a whole, has the same composition as flesh. In flesh, therefore, we have one of the first conditions for the production of blood. In digestion, the muscular fibre, like boiled white of egg, becomes soluble and capable of entering the blood ; and it would be almost pedantic, with our experience of the nutritive process in carnivora, to ask for proof that digested muscular fibre again acquires in the body all the characters of the albumen of blood. It would be, however, easy to supply this proof, since muscular fibre can be converted into albumen even out of the body, by a process, the ultimate cause of which we consider identical with that which effects the solution of food in the stomach. If we leave muscular fibre covered with water, and exposed to the influence of the air, a very small part of it passes into decomposition, and by the action of this the whole of the rest becomes liquid and soluble in water ; the solution, when heated, coagulates to a white solid mass, which is identical in all its properties with the coagulated albumen of blood. If we examine milk that important alimentary substance which, prepared in the body of the mother, is supplied by nature to the body of the young animal for its development we find in it, in the shape of caseine, a substance which contains, like albumen, sulphur and nitrogen ; and the absence of every other nitrogenous compound in milk, renders it perfectly certain that from caseine alone the chief constituent of the young animal's blood, as well as, its muscular fibres, membranes, &c., are formed in the first stage of its life. Caseine is, in its properties, distinct from albumen and NUTRITION IN CARNIVORA. 3'73 tibrine. It is held in solution in milk by an alkali, and may be heated to boiling without coagulation. Diluted acids, which do not coagulate albumen, easily separate the caseine from milk ; it is easily coagulated in the cold by diluted acetic acid, and separates in the form of a jelly or of thick flocculent masses, which, even after boiling with water, dissolve with extreme facility in weak alkaline liquids ; a property by which caseine is very essentially distinguished from coagulated albumen and muscular fibre. The analysis of caseine has proved that this body also contains the same elements, and in the same proportion, as albumen and fibrine, with the exception that it contains a little less sulphur. It is therefore plain that in the caseine of milk the young animal receives the fundamental consti- tuent of its blood in a different form, one, however, the best adapted for the development of its organs. We can now understand the nutrition of the carnivora and of the sucking young of mammalia. The carnivora live on the blood and flesh of those animals which live on grass and grain. This blood and flesh is in all respects identical with their own ; the suckling receives its blood from the blood of its mother. In a chemical sense we may say that the carnivorous animal, to live, consumes itself, while the suckling consumes its mother. Its nourishment is, in its chief constituent, identical with the chief constituent of its blood from which its organs are developed. The process of nutrition in graminivorous animals appears at first sight altogether different. Their digestive organs are less simple, and their food consists of vegetables, which in form and quality have not the smallest resemblance to milk and flesh. The question as to their nutritive properties was, in fact, not many years ago, an apparently insoluble enigma, and we now see how it was possible for the most acute and distin- guished physicians to regard the stomach as the abode of a conjuror, who, if respectfully treated, and in good humour, can change thistles, hay, roots, fruits, and seeds, into blood and flesh ; but when angry, despises or spoils the best food. 374 LETTERS ON CHEMISTRY. All these riddles have been solved with certainty by che- mistry. It has been proved that all such parts of plants as serve for food to animals, contain certain constituents easily distinguished from others by giving off when burning the smell of burnt wool. It is found that animals require for their support less of any vegetable food in proportion as it is richer in these peculiar matters, and cannot be nourished by vegetables in which these matters are absent. These important products of vegetation are especially abundant in the seeds of the different kinds of grain, and of peas, beans, and lentils ; in the roots and the juices of what are commonly called vegetables. They exist, however, in all plants, without exception, and in every part of plants in larger or smaller quantity. These nitrogenised forms of nutriment in the vegetable kingdom may be reduced to three substances, which are easily distinguished by their external characters. When the newly -expressed juices of vegetables are allowed to stand, a separation takes place in a few minutes. A gelatinous precipitate, commonly of a green tinge, is deposited, and this, when acted on by liquids which remove the colouring matter, leaves a grayish white substance, well known to druggists as the deposit from vegetable juices. The juice of grasses is especially rich in this constituent, but it is most abundant in the seeds of wheat, and of the cerealia generally. It may be obtained from wheat flour by a mechanical operation, and in a state of tolerable purity ; it is then called gluten, but the glutinous property belongs, in part, to an oily substance, present in small quantity. This substance, stored up in the seeds of the cerealia, is insoluble in water. The second nitrogenised compound remains dissolved in the juice after the separation of the fibrine. It does not separate from the juice at the ordinary temperature, but is instantly coagulated when the liquid containing it is heated to the boiling point. When the clarified juice of nutritious vegetables, such as cauliflower, asparagus, mangel-wurzel, or turnips, is made to BLOOD CONSTITUENTS IN VEGETABLES. 375 boil, a coagulum is formed, which it is absolutely impossible to distinguish from the substance which separates as a coagulum, when the serum of blood, or the white of an egg, diluted with water, are heated to the boiling point. The third of these important vegetable principles is chiefly found in the seeds of peas, beans, lentils, and similar leguminous seeds. It may be extracted from their meal by cold water, and kept in solution. In this solution it resem- bles the others, but is distinguished from them in this, that its solution is not coagulated by heat. When the solution is heated or evaporatedj a skin forms on its surface, and the addition of an acid causes a coagulum, just as in animal milk. The analysis of these three vegetable principles has led to the interesting result, that they all three contain sulphur and nitrogen and the other constituents in the same propor- tion, and, what is still more remarkable^ that they are identical in composition with albumen, containing the same elements in the same proportion as that chief constituent of blood. How admirably simple, after we have acquired a know- ledge of this relation between plants and animals, appears to us the process of formation of the animal body, the origin of its blood and of its organs ! The vegetable sub- stances, which serve for the production of blood, contain already the chief constituent of blood, ready formed, with all its elements. The nutritive power of vegetable food is directly proportional to the amount of the sanguigenous compounds in it ; and in consuming such food, the herbi- vorous animal receives the very same substances which, in flesh, support the life of carnivora. From carbonic acid, water, and ammonia, that is, from the constituents of the atmosphere, with the addition of sulphur and of certain constituents of the crust of the earth, plants produce the blood of animals \ for the carnivora consume, in the blood and flesh of the herbivora, strictly speaking, only the vegetable substances on which the latter have fed. These nitrogenised and sulphurised vegetable products, the 376 LETTERS ON CHEMISTRY. albuminous or sanguigenous bodies, assume, in the stomach of the herbivora, the same form and properties as the fibrine of flesh and animal albumen do in the stomach of the carnivora. Animal food contains the nutritive constituents of plants stored up in a concentrated form. A comprehensive natural law connects the development of the organs of an animal, their growth and increase in bulk, with the reception of certain substances, essentially identical with the chief constituent of its blood. It is obvious that the animal organism produces its blood only in regard to the form of that fluid, and that nature has denied to it the power of creating blood out of any other substances, save such as are identical, in all essential points, with albumen, the chief constituent of blood. The animal body is a higher organism, the development of which begins with those substances, with the production of which the life of those vegetables ends which are com- monly used for food. The various kinds of grain and of plants used for fodder, die as soon as they have produced seeds. Even in perennial plants, a period of their existence terminates with the production of their fruit. In the infinite series of organic products which begins with the inorganic- food of plants, and extends to the most complex constituents of the nervous system and brain of animals, the highest in the scalej we see no blank, no interruption. The nutritive part of the food of animals, that from which the chief material of their blood is formed, is the last product of the productive energy of vegetables. If we compare the three nitrogeno-sulphurised vegetable products with the fibrine of flesh, the albumen of blood, and the caseine of milk, in reference to their physical characters, we find that the gluten of wheat-flour has the closest resemblance to the fibrine of flesh ; that that constituent of vegetable juices which is coagulated by heat, is absolutely not distinguishable from the albumen of blood ; and lastly, that the chief constituent of the seeds of the leguminosbo agrees in all its properties and behaviour with the caseine of milk. Hence are^derived the names of vegetable fibrine, vegetable ANIMAL AND VEGETABLE FIBRINE, &c. 377 albumen, and vegetable caseine* which have been most justly given to these three vegetable products, since they perfectly agree in properties with the corresponding animal products. The three nitrogeno-sulphurised or sanguigenous con- stituents of seeds and vegetable juices are never, or at least very rarely indeed, found alone. Thus, in the juice of pota- toes there is found, besides fibrine and albumen, vegetable caseine coagulable by acids ' } and in the seeds of leguminosse there is always, besides the caseine, a certain quantity of albumen coagulable by heat. The so-called gluten of rye meal consists almost entirely of vegetable caseine and vegetable albumen. In wheat flour all three are found. It is worthy of special remark, that animal fibrine and vegetable fibrine, animal albumen and vegetable albumen, animal caseine and vegetable caseine, not only contain respectively the same elements in the same proportions, but also possess like properties. The gluten of wheat-flour (which consists chiefly of fibrine) dissolves almost entirely to a turbid fluid in water, to which hydrochloric acid has been added in the proportion of a drop to each ounce. In this solution, just as in that obtained from flesh in the same way, sea-salt causes coagulation. The coagulum, covered with pure water, and left to putrefy, dissolves almost entirely to a clear fluid, and this occurs equally with the fibrine of flesh. Here the putrefaction of a small portion has caused the solution of the remainder, and in both cases the solution is now found to contain a large quantity of true albumen, coagulable by heat. Lastly. These different substances, whether of animal or * A remarkable proof of the true nature of vegetable caseine is fur- nished by a fact, quite independent of chemical researches, which is recorded by J. Itier in his report. The Chinese, it appears, are in the habit of making a real cheese from peas. For this purpose, the peas are boiled to a thin paste, which is passed through a sieve, and coagulated by the addition of solution of gypsum. The curd is treated like that formed in milk by means of rennet. The solid part is pressed out, and, with the addition of salt, is wrought into cheese in moulds. This cheese gradually acquires the smell and taste of milk cheese. It is sold in the streets of Canton, under the name of Taofoo, and, when fresh, is a favourite article of food with the people. 378 LETTERS ON CHEMISTRY. vegetable origin, yield, in processes of oxidation, the same products ; a fact which chemistry regards as a proof that their elements are also arranged in the same way. These products are sufficiently remarkable to justify us in directing attention to them. When such compounds are acted on by strong potash, a part of their sulphur is taken up by the potash, and the alkaline solution, by the presence of sulphide of potassium, acquires the property of forming, when a drop of solution of sugar of lead is added, an inky fluid, coloured by the sulphide of lead. The further action of the alkali produces from all these sanguigenous compounds two crystal- line products, allied to the organic bases, namely, tyrosine and leudne* the latter of which Prout first found in putrid cheese, and Crum in putrescent gluten. Besides these crys- tallised products, there are formed by the action of alkalies on sanguigenous substances several volatile oily acids, such as butyric and valerianic acids. When the oxidation is conducted in acid liquids, we obtain numerous and very remarkable products, among which are hydrocyanic acid, oil of bitter almonds (hydride of benzoyle)^ benzoic acid, formic, acetic, propylic, butyric, and valerianic acids, as well as several of the corresponding aldehydes ; so that probably no other organic substances can in this respect be compared to the sanguigenous bodies, animal or vegetable. The consideration that vegetable albumen, vegetable fibrine, vegetable caseine, animal fibrine, and animal caseine, are the only nutritive matters in the animal or vegetable kingdoms from which, in the process of nutrition, the chief constituent of the blood, and, in the vital process, all the tissues of the animal body are formed, has led chemists and physiologists to give to these five nitrogeno-sulphurised substances the name of plastic elements of nutrition. To these five may be added the albumen of the blood, since, as an element of the animal body it becomes a nutritive article * Leucine acquires now a greater importance, since, besides its occur- rence as a product of the oxidation as well as of the putrefaction of these substances out of the body, it has lately been detected ready formed in the body, namely, in the fluids of the liver of the calf. PHYSICAL PROPERTIES OF ORGANS AND TISSUES. 379 of food. (This is to be considered as synonymous with the shorter and more convenient term of scyiguigenous bodies, which I have occasionally used, as well as with the terms nitrogeno-sulphurised, azoto-sulphurised, and albuminous bodies, which are also frequently used. W. G.) There is, indeed, no part of an organ, possessing a form or structure of its own, the elements of which are not derived from the albumen of the blood. All organised tissues in the body contain a certain amount of nitrogen. Many of the physical properties of the organs or tissues depend on the presence of their non-nitrogenous constituents, namely, of water and fat. These bodies assist in the changes and processes, by which organised structures are formed. Fat has a share in the formation of cells ; and on water depends the fluidity of the blood and of all other juices. So also the milk-white colour of cartilage, the transparency of the cornea, the softness, plasticity, flexibility, and elasticity of muscular fibre and of membranes, the silky lustre of fasciae and tendons; all depend on a fixed proportion of water in each case. Fat is a never-failing constituent of the sub- stance of the brain and nerves ; hair, horn, claws, teeth, and bones, always contain a certain amount of water and fat. But in these parts water and fat are only mechanically absorbed, as in a sponge, or enclosed in drops, as fat is in cells, and they may be removed by mechanical pressure, or by solvents, without in the least affecting the structure of the parts. They never have an organised form peculiar to them- selves, but always take that of the parts, the pores of which they fill. They do not belong, therefore, to the plastic con- stituents of the body or of the food. 380 LETTERS ON CHEMISTRY. LETTER XXX. Respiratory Food Fat, Butter, Sugar of Milk Starch, Cane-sugar, Grape- sugar, &c. Sugar of Milk Its Properties ; oxidisable in presence of Alkalies ; undergoes the Lactic Fermentation in contact with Caseine ; is identical in composition with Grape-sugar Starch ; its Varieties ; convertible into Dextrine and Grape-sugar Table of the Relative Pro- portions of the Plastic to the Non-nitrogenous Constituents in different Articles of Food Best Proportion supplied by Nature in Milk and Grain, or in some kinds of Flesh Popular Mixtures, such as Beans and Bacon, Peas and Pork, Potatoes and Meat, &c., give good Proportions which have been indicated by the instinct Alcohol as a Respiratory Element of Food Relation of Food to Work Performed Rations of Labouring Men, Soldiers, &c. Feeding of Stock ; Fattening The Plastic Matters do not contribute to the Animal Heat Functions of Sugar, &c. Accumulation of Fat : its Origin from Sugar Table of the Comparative Value of Fat, Starch, Sugar, Alcohol, and Flesh, in Regard to the Heat derived from them in the Body Proportion of Nitrogen to Carbon in the Tissues and Excreta. THE food of all animals, besides the plastic or sangui- genous constituents, from which the blood and the organs are derived, contains, at all times, and under all circum- stances, a certain amount of substances devoid of nitrogen and of sulphur. Flesh, the food of the carnivora, contains a certain quantity of fat ; milk contains fat (in butter), and along with this an easily crystallisable body, sugar of milk, which is obtained from the whey of sweet milk by evaporation. The food of the herbivora always contains a substance resembling sugar of milk, and closely allied to it in chemical characters. (Starch, cane and grape sugar,. gum, &c.) The properties of milk-sugar, considered as a constituent of milk, and as a product of the vital process in animals, are peculiarly interesting. Hitherto this kind of sugar has been found only in milk, and, according to recent researches, although in very small proportion, in eggs. It occurs in PROPERTIES OF MILK SUGAR. 381 commerce in thick crystalline crusts, which are usually yel- lowish, yellowish-brown, or dirty, from want of care and cleanliness in its preparation. By re-crystallisation, and the use of animal charcoal, to decolorise the solution, it is obtained in four-sided prisms, acuminated by four planes, which are dazzling white, hard, and gritty to the teeth. Crystallised milk-sugar dissolves in five or six parts of cold water, without forming a syrup ; the crystals, placed on the tongue, have a weak sweet taste, which is stronger in the solution. The property of fermenting, when left to itself at a moderate temperature, which milk possesses, depends on the presence of milk-sugar. Fermented milk yields, when distilled, true spirits, which has, however, an offensive smell of butyric acid and rotten cheese. This spirit, prepared from mare's milk, is in general use in Tartary and in the country of the Khirgeses and Kalmuks. The facility with which, under certain circumstances, milk-sugar undergoes another trans- formation, and is converted into lactic acid, is well known to every one from the fact that milk so readily turns sour. (See Letter XVIII.) Milk-sugar is distinguished by the power of absorbing oxygen when free alkali is present. If a solution of it be rendered alkaline by means of ammonia, and a salt of silver added, the oxide of silver, when the solution is warmed is reduced, either as mirror-like ^deposit on the glass, or in grey flocculi. A solution of milk-sugar to which potash is added, dissolves oxide of copper, with a beautiful blue colour. This solution, when heated becomes of a fine red, the copper separat- ing as red suboxide. In these instances the oxygen of the oxides is taken up by the elements of the milk-sugar, entirely in the case of silver, and to the extent of one-half in that of copper. An alkaline solution of milk-sugar dissolves peroxide of iron and other oxides, and the same solution decolorises blue indigo, which is dissolved in the colourless or deoxidised form, yielding a true indigo bath, fit for dyeing. By the influence of many ferments, and with the greatest facility in presence of lime, the lactic acid derived from milk- sugar is converted into butyric acid, which belongs to the group 382 LETTERS ON CHEMISTRY. of fatty or oily acids. When oxidised by means of nitric acid, milk-sugar yields carbonic, oxalic, and mucic acids. Finally, if to a solution of milk-sugar in water we add some sulphuric acid, the milk-sugar is very rapidly converted into grape-sugar. Crystallised milk-sugar contains carbon and the elements of water, oxygen, and hydrogen, in such proportions that if we suppose the whole of its hydrogen replaced by the equi- valent quantity of oxygen, the result will be carbonic acid. If we represent milk-sugar by the formula C 12 H 12 12 , and replace the 12 eqs. of hydrogen by 12 eqs. of oxygen, we have C 12 12 12 or C 12 0^, which is = 12 C 2 ; that is, 12 eqs. of carbonic acid. Sweet fruits and sweet vegetable juices owe their sweet taste to three kinds of sugar, of which two are crystallisable, while the third is always soft or of syrupy consistence. This last kind occurs in most fruits. (Mitscherlich.) Beet-root and carrots contain the same kind of sugar as the juice of the sugar-cane ; honey contains the same kind as grapes. Of these sugars, grape-sugar, in its character and composition, most resembles milk-sugar. Dried grape-sugar has the same composition as crystallised milk-sugar ; and in its action on metallic oxides, such as oxide of silver, oxide of copper, and peroxide of iron, and on indigo, as well as in the property of passing under certain circumstances into lactic and butyric acids, it agrees exactly with milk-sugar. Cane-sugar differs from crystallised milk-sugar and from dried grape-sugar in composition only by the elements of 1 eq. of water, its formula being Cj 2 H n O u ; but by contact with ferments or acids, it takes up into its composition this 1 eq. of water, and passes with great facility into grape-sugar. The most universally diffused substance in the vegetable kingdom and in the food of herbivora, which in the process of their nutrition plays the same important part as milk- sugar does in that of carnivora, is starch, which appears at first sight the most remote from milk-sugar in its properties. Starch is found deposited in rounded grains in the seeds of the cereals and leguminosse, in roots and tubers, and in wood, and after breaking up the cells which enclose it, may STARCH. 383 be obtained by washing with water. If potatoes, unripe apples or pears, chestnuts, acorns, radishes, arrow-root, the pith of certain palms, wheat, and other grains, be rubbed down, and the paste washed with water on a fine sieve, the white and turbid fluid which passes through deposits starch in the form of a snow-white very fine powder. It occurs in commerce in various forms. The finest starch from wheat is known as hair powder j sago is the starch of the sago palms, granulated and dried as well as slightly baked together by heat ; arrow-root is that of the plant of that name, Maranta arundinacea ; mandiocca is that of latropha Manihot (the last three kinds, as sold on the continent, are chiefly potato starch). All kinds of starch have the same composition and the same chemical characters ; except the peculiar starch (inulme) of Inula helenium, of the dahlia- root, and many lichens ; all give with hot water a more or less fluid or gelatinous paste, which strikes a splendid indigo blue colour with solution of iodine. It has already been mentioned, in Letter XVIII., that starch, by the influence of the gluten of grain in the ger- mination of corn, or by that of sulphuric acid, is converted into grape-sugar. When mixed with a hot infusion of malt, starch-paste or jelly becomes at once fluid ; there is at first formed a substance like gum, known as starch-gum or dextrine, which, by the continued action of the malt, is entirely changed into grape-sugar. A precisely similar action is exerted on starch- jelly by saliva including air. A mixture of saliva with starch- paste, exposed to the temperature of the human body, becomes more fluid and sweet, and, by means of a proper quantity of saliva, the whole starch is transformed into grape-sugar. The difference in external form and characters between starch and grape-sugar is thus, it is easy to see, almost entirely destroyed in the digestive process. Nature has so arranged it, that, during mastication, there is added to amy- laceous food a substance, by the action of which in the stomach the starch is transformed into a substance which agrees in its composition and in its chief properties with sugar of mijk. 384 LETTERS ON CHEMISTIIY. The amount of starch in the flour of different kinds of grain, in peas, beans, lentils, and potatoes, is very large. Wheat and rye-flour contain from 60 to 66 ; barley and lentils, 40 to 50 ; maize-flour about 78 ; rice as much as 86 ; potatoes (dry) above 70 per cent, of starch. The fat of butter and that of flesh contain carbon and hydrogen very nearly in the same relative proportion as starch and the various sugars ; these differ from fat chiefly in containing more oxygen. For the same quantity of carbon, fat contains nearly ten times less oxygen than starch, &c. ; and it is therefore easy, by adding oxygen, to convert, in our calculations, a given amount of fat into starch. In this way we find that ten parts of fat correspond to twenty-four of starch. In like manner, by deducting a certain amount of water, we can reduce milk-sugar to its equivalent of starch ; and, by thus reducing all the non- nitrogenous elements of food to their equivalent values expressed as starch, we can readily compare the most important articles of food in regard to the proportions of plastic or sanguigenous, and of non-nitrogenous substances which they contain. This is done in the following table : Relative Proportions of the Plastic to the Non-nitrogenous Con- stituents in Different Articles of Food. Plastic. Cow's Milk contains, for 10 Human Milk ,, 10 Lentils ,, 10 Horse Beans , 10 Peas , 10 Fat Mutton , 10 Fat Pork , 10 Beef 10 Hare , 10 Veal , 10 Wheat Flour , 10 . Oatmeal , 10 Rye Flour , 10 Barley , 10 Potatoes, white , 10 blue , 10 Rice , 10 Buckwheat Flour , 10 Non-Nitrogenous (as Starch). 8-8fat, 10-4 milk-sugar. 40 21 22 23 27 = 11 "25 fat. 30=12-5 17 = 7'08 2= 0-83 ,, 1= 0-41 46 50 57 57 86 115 123 130 COMPOSITION OF FOOD. 335 The relative proportions of the plastic constituents in milk to its butter and milk-sugar, that of the sanguigenous matter in flesh to its fat, and that of the plastic matter of grain, potatoes, and the seeds of the leguminosse, to their starch, are not constant. They vary in milk with the food ; fat or fattened flesh contains more fat than that which is lean; and the difference between the two kinds of potato shows how great may be the variation in different varieties of the same plant. But the above may be regarded as average numbers, lying between the opposite extremes in each case. We may regard as constant the following results ; namely, that peas, beans, and lentils contain, for 1 part by weight of plastic matter between 2 and 3 of non- nitrogenous matter, reckoned as starch ; that grain, such as wheat, rye, barley, and oats contain between 5 and 6 parts ; potatoes, from 8 to 11 parts ; rice and buckwheat, from 12 to 13 parts of the latter to 1 of the former. Of all food, lean flesh is richest in plastic constituents. Omitting the inorganic constituents, 17 parts of lean beef contain as much plastic or sanguigenous matter as 56 parts of wheat flour, or 67 of rye-flour, or 96 of white potatoes, or 133 of rice. In comparing these kinds of food, we must bear in mind, that in their natural state they all contain a certain amount of water, which must be taken into account ; 17 parts of dry beef, in which are 7*08 parts of fat, contain, in the natural state, 32 parts of water. As wheat-flour contains 15 per cent, of water, the 49 parts (17 -f- 32) of fresh beef corre- spond to 66 parts of flour. It is obvious, that by a due mixture of these articles of food, we can obtain a diet of a composition analogous to that of milk or of wheaten bread. By the addition of bacon or fat pork to peas, beans, or lentils ; of potatoes to beef ; of fat bacon or ham to veal ; of rice to mutton ; we increase in each case the proportion of non -nitrogenous matter. The same result is obtained by the use of fermented liquors, which, when taken with lean flesh and little bread, yield a diet approaching to milk, and, with fat meat, one approaching 38G LETTERS ON CHEMISTRY. to rice or potatoes, in the relative proportions of plastic and non-nitrogenous constituents. A glance at these relations is sufficient to convince us, that, in choosing his food (when a choice is open to him), and in mixing the various articles of diet, man is guided by an unerring instinct, which rests on a law of nature. This law prescribes to man, as well as to animals, a pro- portion between the plastic and non-nitrogenous constituents of his whole diet, which is fixed within certain limits, within which, it may vary, according to his mode of life and state of body. This proportion may, in opposition to the law of nature and instinct, be altered beyond these limits by necessity or compulsion ; but this can never happen without endangering the health, and injuring the bodily and mental powers of man. It is the elevated mission of science to bring this law of nature home to our minds ; it is her duty to show why man and animals require such an admixture in the constituents of their food for the support of the vital functions, and what the influences are which determine, in accordance with the natural law, changes in this admixture. The knowledge of this law elevates man, in regard to an important function which he possesses in common with the lower animals, above the level of those beings which are destitute of reason, and supplies him, in the regulation of those bodily wants which are essential to his existence and prosperity, with a protection, which the lower animals do not require, because in them the commands of the instinctive law are not opposed or overpowered by the allurements of sense nor by a perverted and resisting will. The inquiry as to the ultimate foundations on which this law of instinct rests, which compels men and animals to consume, along with the plastic matters from which their organs are formed, certain non-nitrogenous bodies, which take no direct share, by their elements, in the formation of these organs, and the further inquiry as to the part which these substances perform in the vital process, are easily answered when we compare the constituents of the body AMOUNT OF FOOD CONSUMED BY ANIMALS. 387 with those of the food, and consider the latter as the causes or conditions of those effects which they produce in the living body. A working horse consumes, in a year, 5475 pounds of hay, and 1642 pounds of oats.* An adult pig, weighing 120 pounds, consumes, in the same time, 5110 pounds of potatoes, t With this prodigious mass of food, which, in the pig, amounts to more than forty times the weight of its body, the weight of these animals, at the year's end, either does not increase, or the increase is a mere fraction of the weight of the food. So it is with the food of man. In an adult, whose weight is not perceptibly altered at the year's end, the proportion of the parts and their compositions are the same as at the beginning of the period. The whole quantity of food taken in 365 days, has not been employed in increasing the size or weight of his body, but has only served to produce a series of effects. The fourteen pounds of potatoes, daily consumed by the pig, produced in its body a certain quantity of mechanical force, by which the motion of its blood, of its juices, and of its limbs was effected. The constituents of the food served to keep the mechanism in action. A result precisely similar was effected by the fourteen pounds of hay and the four and a half pounds of oats, daily consumed by the horse ; with this difference, however, that this amount of food enabled the horse to expend a certain amount of mechanical force externally. The food produced in his body an excess of force, by which his limbs were enabled, without injury to health, to overcome a certain sum of resistance, that is, to perform a certain amount of work. In the body of the man, the bread, flesh, and vegetables produced the same effect as in the horse ; but, in addition to the mechanical force, which determined the involuntary motions of his internal organs and the voluntary motions of his muscles in his work, the food also produced a certain * Ann. de Chim. et de Phys., LXXL, 136. t Ann. de Chim. et de Phys., Nouvelle Serie, XIV., 443. c c 2 388 LETTERS ON CHEMISTRY. sum of effects, manifested in the action of the senses and of the intellect. We know that when food is withheld, the body of man and of all animals loses weight every second ; that the decrease or loss in the most important organs in a given time, stands in a certain ratio to the manifestations of force produced, in the same time, by his organs or his limbs ; that by the food, the weight of the body, and the power of producing new manifestations of force, is restored ; that in a state of rest, man and animals require less food than in that of motion or exertion. We know further, that it is not a matter of indifference what is the quality of the food which the man or beast must daily consume, in order to recover, undiminished, the original power, and to perform, on the following day, the same amount of work as on the first, or to produce the same manifestations of force through the nervous system, or mental manifestations. Innumerable observations, made during centuries, have demonstrated beyond a doubt, that different forms of food are extremely unequal in regard to the production and restoration of these powers or forces ; that wheat surpasses rye, that rye surpasses potatoes and rice, and that flesh surpasses all other food in reference to these effects. These observations, made by all mankind, have shown, that a horse, fed on potatoes, cannot perform anything like the same amount of work as one fed on hay and oats ; and, lastly, that the power of daily labour, available in man, may be measured by the quantity of the plastic or sanguigenous constituents contained in the flesh and bread he consumes.* It is obvious, that the plastic constituents of food are the * The daily ration in bread, given to a soldier, is, in Grammes. France . . . 750 (Wheat.) Belgium Sardinia Spain South Germany 775 737 ;; 670 ,, 900 ( Wheat, | Rye, Barley. 1 ) North Germany & Russia 1000 (Rye.) The gramme is 15 '44 grains, 1000 grammes is equal to about 2 Ibs oz. avoirdupois, 750 grammes are equal to 1 Ib. 10^ oz. ORGANIC FORCES DEPENDENT ON FOOD. 389 proximate conditions or causes of the production of force in the organism, and of all mental manifestations, such as those of sense, emotion, or intellect. We can readily understand this, when we reflect that all the phenomena of motion in the animal organism, all the effects which an animal produces by its brain or its muscles, are determined by, or depend on the organised structure of his body that the unorganised parts, which have no form, such as water and fat, have no vital properties, and cannot change their place or relative position by any power inherent in themselves. But if the effects producible on the body of a man or beast, whether in his organs of sense, his brain, or the organs of the voluntary and involuntary motions, depend on the number or size of the organised parts, it is evident that the amount or the duration of these effects must be in propor- tion to the mass of the individual parts of which the organs consist j the cerebral manifestation must be in proportion to the mass of the brain, the mechanical effects to the mass of muscular substance. With the decrease of the mechanical apparatus for the production and external manifestation of force, with the wasting of the substance of the muscles and nerves, the power of making such manifestations diminishes ; with the renovation and restoration of these organised structures or tissues in the process of nutrition, the power of producing repeatedly the same manifestations of force, of performing the same mental or bodily labour, is regained. All these organised tissues, all the parts, which in any way manifest force in the body, are derived from the albumen of the blood all the albumen of the blood is derived from the plastic or sanguigenous constituents of the food, whether animal or vegetable. It is clear, therefore, that the plastic constituents of food, the ultimate source of which is the vegetable kingdom, are the conditions essential to all pro- duction or manifestation of force, to all those effects which the animal organism produces by means of its organs of sense, thought, and motion. 390 LETTERS ON CHEMISTRY. In this relation, in this dependence of the animal on the vegetable kingdom, a new and admirable connection is un- folded to the human mind. Plants, which serve as food to animals, are the producers of the plastic constituents of food, and hence are accumula- tors of force. In repose and in sleep, animals return to the condition of plants ; the formless constituents of their blood become organised portions of their tissues ; and while these tissues, in their turn, are resolved in the vital process into formless or into inorganic compounds, the force stored up in them is manifested in the most various effects, like a galvanic battery, the peculiar properties of which are deter- mined by a certain arrangement of its elements, and which consumes itself in giving rise to new manifestations, mag- netic, electrical, or chemical. The relations of the plastic constituents of food to the vital process in the animal body, appear thus to be cleared up. These substances, restoring the original weight of the organised tissues, part of which has been consumed, and has been separated, render possible the continued manifestation of all vital actions. A horse, fed on potatoes, and compelled to work, loses weight ; when he does no work, his weight remains unchanged. It is obvious that the work performed consisted in a waste or consumption of bodily parts ; and the quantity of plastic substances present in the whole amount of potatoes con- sumed did not suffice for the full restoration of the wasted tissues. More was consumed than the food given could replace, and hence the animal began to show signs of emacia- tion and weakness. On the other hand, the horse, which is abundantly fed with hay and oats, can perform a certain amount of labour, without any loss of weight being next day perceptible. When the same amount of food is given to the animal in a state of rest, it becomes heavier, increasing in weight up to a certain point. It is plain that the food produces in the body of the* horse a certain sum of force, which may be employed either within the body itself, or in overcoming external resist- KELATION BETWEEN FOOD AND LABOUR. 391 ance. If this force be used in the performance of work, the weight of the body remains unchanged ; but if employed within the organism for vital purposes, the body increases in bulk in all its parts. It follows from this, that the working power of an animal stands in a fixed ratio to the excess of food, which, in the state of rest, increases the weight of the body. If our interpretation of this eternal and immutable law of nature be not false, the proportion of the plastic constituents, required by the working man in his daily food, cannot be less than that which nature herself prepares for the develop- ment and growth of the human body and for its increase in all its parts. Such is the proportion found in human milk. The diet of the working man should therefore contain, for foui* parts of non-nitrogenous constituents, one part of plastic nutritive matter. This, indeed, is saying no more than is well known, since the world and its inhabitants have existed, that the man who has to do that amount of work which, according to the conditions of his organism he can perform, must add to his bread a certain amount of flesh ; that according to the structure of his body the proportion of the plastic to the other constituents of the food must be increased, if he has to do more than average work : and that, in the state of rest he requires a smaller proportion of plastic nourishment. It follows further, that when a child, deprived of the benefit of receiving the necessary supply from the mother is fed on cow's milk, which contains a larger proportion of plastic matter, milk-sugar (or cane-sugar) should be added to the cow's milk ; or when it is fed on flour paste, cow's milk should be added, as experience has long ago taught us, in order to obtain the same effects as from the mother's milk.* It is further obvious, as indeed every one knows to be the case, that, if a child or young person be compelled by circum- * According to a calculation by Knapp, a soldier on the rations men- tioned at p. 388, consumes, in his daily food, for 10 parts of plastic, 47 parts of non-nitrogenous matter. 392 LETTERS OX CHEMISTRY. stances to expend in work external to the body, a part of the force produced in the organism, and if this excess of ex- penditure be not compensated by proper food, or cannot be compensated, because his body can only digest a certain quantity of food, his bodily development must be deranged and impeded. The admirable experiments of Boussingault prove, that the increase in the weight of the body in the fattening or feeding of stock (just as is the case with the supply of milk obtained from milch cows), is in proportion to the amount of plastic constituents in the daily supply of fodder. These experiments were carried on for months with pigs, animals possessing in a high degree the power of converting the elements of their food into parts of their body. A pig was fed exclusively on potatoes, under which feeding it did not increase in weight ; but an increase in weight was observed when the animal got a diet composed of potatoes, butter- milk, whey, and kitchen refuse. The greatest increase took place when the food was what was called fattening fodder, consisting daily of potatoes (974 lb.); ground corn (O90 Ib.) ; rye flour (0'64 lb.) ; peas (0'68 lb.) ; butter-milk, whey, and kitchen refuse (0'92 lb.) Analysis and calculation show that the pig received, in these three modes of feeding, food of the following propor- tions of the plastic to the other constituents.* Proportion of the plastic to the non-nitrogenous constituents, the latter calculated as starch. The pig consumed Plastic. Non-nitrogenous. In potato fodder, for . 10 87 In mixed fodder, for . 10 71 In fattening fodder, for . . 10 55 It is easy to see, that this last mixture contains the same proportion of plastic and non-nitrogenous matters as is found, on an average, in grain. German agriculture has been led by experience to a very * Ann. de Chim. et. de Phys., Nouvelle Serie, XIV., 419. GERMAN AGRICULTURE. 393 simple method of converting potatoes into a fattening fodder quite similar to the above-mentioned, and tg grain in its composition. This method is the foundation stone of the profitable agriculture of Germany; and it consists in re- moving, entirely or to a great extent, and by a purely chemical process, the non-nitrogenous part of the potatoes, and using the residue, which contains all their plastic consti- tuents, to feed stock. The potatoes are reduced to a thin paste, and placed in contact with malt, by the action of which the starch is converted into sugar. The mash, as it is called, is now mixed with beer yeast, which causes it to ferment, and the whole sugar is thus destroyed. By dis- tilling the fermented mash, the starch of the potatoes is obtained in the form of spirits, and the residue or dregs forms the most valued food for fattening stock. The opinion prevalent in other countries, that the German farmer is a distiller, for the sake of the spirits, is decidedly erroneous. He distils spirits, in order to obtain, at the cheapest rate, the fodder which is indispensable to him. This method of concentrating the plastic matter, proper for the production of blood and flesh, is one of the numerous instances in -which empirical experiment has preceded theory. At first, the only object was to obtain the spirits ; then it became desirable to make a profitable use of the residue ; and finally, it was found, that the property of serving as fattening food was increased in potatoes, by the process of mashing and fermentation. As far ascegards the propaga- tion of this kind of truths, want and necessity are teachers, whose influence and power of convincing men are mightier than all science. From what has been said, we can deduce in a manner free from doubt, the true significance of the plastic constituents of food. Becoming organised parts of the living body, they determine the continuance of all vital phenomena. If we now consider that the animal body is not merely a source of mechanical power and of vital actions, but also an apparatus for producing heat ; that the amount of heat daily produced in the body of an adult man would suffice, in the 394 LETTERS ON CHEMISTRY. course of a year, to heat from twenty to twenty-five thousand pounds of water from the freezing to the boiling point ; if we bear in mind, that the animal heat is a result of the com- bination, in the body, of the oxygen taken up in respiration, with certain constituents of the food or of the body ; and that the daily amount of heat produced is in direct propor- tion to the amount of oxygen consumed ; the most superficial observation teaches us, that the elements of the plastic con- stituents of food can have only a very secondary share in the production of that heat, thus daily produced. In fact, if we compare the amount of the plastic matters daily consumed with that of the oxygen consumed in the same time, we find that the combustible elements of the former are very far from sufficing to convert into carbonic acid and water the whole of the oxygen which has entered the blood. The animal body takes up far more oxygen ; the horse, for example, five times, the pig six times, as much as would be required for the most perfect combustion of the plastic matter in the food. If, therefore, the combustible elements of the plastic con- stituents of food served for the production of heat, the whole amount of these substances consumed by the horse in his hay and oats, by the pig in its potatoes, would only suffice to support their respiratory process, and consequently their animal heat, in the horse for 4^ hours, in the pig for 4 hours daily ; or, if confined to plastic food, they would require to consume five or six tjmes as much of it. But even in this last case, it is exceedingly doubtful whe- ther these substances, considering their properties, would, in the circumstances under which they are presented to oxygen in the organism, produce the necessary temperature of the body, and compensate for the loss of heat ; for of all organic compounds, the plastic constituents of food are those which possess in the lowest degree the properties of combustibility and of developing heat by their oxidation. Of all the elements of the animal body, nitrogen has the feeblest attraction for oxygen; and, what is still more remarkable, it deprives all combustible elements with which NITROGEN RENDERS BODIES LESS COMBUSTIBLE. 395 it combines, to a greater or less extent, of the power of com- bining with oxygen, that is, of undergoing combustion. Every one knows the extreme combustibility of phosphorus and of hydrogen ; but by combining with nitrogen they produce compounds entirely destitute of combustibility and inflamma- bility under the usual circumstances. Phosphorus takes fire at the heat of the body, and4s easily oxidised by dilute nitric acid. The phosphide of nitrogen, a white body, like chalk, only takes fire at a red heat, and in oxygen gas, but does not continue to burn, and is not attacked by dilute nitric acid. Ammonia, a compound of nitrogen with hydrogen, contains, in two volumes, three volumes of hydrogen j but in spite of this large proportion of an element so inflammable and com- bustible, ammonia cannot be set on fire by a red hot body, and even in pure oxygen it does not continue to burn. Almost all compounds of nitrogen are, compared with other bodies, difficultly combustible, and are never regarded as fuel, because when they do burn, thay develop only a low degree of heat, not sufficient to raise the adjacent parts to the kindling point. Only cyanogen, which contains much carbon, and hydrocyanic acid, among compounds of nitrogen, are inflammable in the gaseous form, and continue to burn when kindled. It is precisely so with albumen in the alkaline blood. If we compare its power of combining with oxygen with that possessed by the non-nitrogenous bodies, milk-sugar, grape- sugar, or fat, it has much the same relation to them as silver has to iron. If we would divide the elements of the body, according to their combustibility, like the metals, into the classes of common and noble, then the organised structures of the body consist of the noblest substances found in organic nature. Wherever it is vouchsafed to the feeble senses of man to cast a glance into the depths of creation, he is compelled to acknowledge the greatness and wisdom of the Creator of the world. The greatest miracle which he is capable of compre- hending is that of the infinite simplicity of the means, by the co-operation of which order is preserved in the universe 396 LETTERS ON CHEMISTRY. as well as in the organism, and the life and continued exist- ence of organised beings are secured. Without the powerful resistance which the nitrogenised constituents of the body, in consequence of their peculiar nature as compounds of nitrogen, oppose, beyond all other parts, to the action of the air, organic life could not subsist. If the albumen of the blood, which is derived from the plastic portion of the food, possessed in a higher degree the power of supporting respiration, it would be utterly unfit for the process of nutrition. Were albumen, as such, destructible or liable to be altered in the circulation by the inhaled oxygen, the relatively small quantity of it daily supplied to the blood by the digestive organs would quickly disappear ; and the slightest disturbance of the digestive function would of necessity put an end to life. As long as the blood contains, besides albumen, other substances which surpass it in attraction for oxygen, so long- will the oxygen be unable to exert a destructive action 011 this, the chief constituent of the blood ; and the significance of the non-nitrogenous part of the food is thus made clear. Starch, sugar, and fat, serve to protect the organised tissues, and, in consequence of the combination of their elements with oxygen, to keep up the temperature of the body. The sulphurised and nitrogenous constituents of food determine the continuance of the manifestations of force ; the non-nitrogenous serve to produce heat. The former are the builders of organs and organised structures, and the pro- ducers of force ; the latter support the respiratory process ; they are materials for respiration. The necessity for the simultaneous presence of both, of the plastic and respiratory materials, and for their due admixture, is now obvious. The sum of both, daily required by the body, depends on the amount of oxygen taken up ; their relative proportion depends on the causes of loss of heat and expenditure of force. With an equal expenditure of force in work, a man requires, in summer, a less supply of respiratory food than in winter in the south less than in the north ; and if men USES OF SUGAR, &c., IN THE BODY. 397 consume equal weights of these substances in different seasons or climates', they are found in one case when, for example, they contain vegetable acids and sugar to be richer in oxygen, and in the other to be richer in combustible elements, as in the instance of the train oil and blubber of the inha- bitants of Arctic regions. Neither the formation of organs from the constituents of the blood, nor their employment in manifestations of force, can be conceived without the presence of non-nitrogenous substances. We find, in eggs, for 10 parts of albumen, 15 parts of non-nitrogenous matter (fat, calculated as starch), the greater part of which disappears during incubation. By the combination of the elements of the fat with the oxygen of the air, a certain amount of heat is developed, and the action of the external heat of incubation assisted. Carbonic acid and water are formed, and, by the latter, the water lost by evaporation is in part replaced. Lastly, by the presence of the fat, the influence of the oxygen is kept in equilibrium, and reduced to the due measure of what is necessary for the formation of the tissues. But an animal which respires consumes a much larger amount of oxygen than is used for similar purposes in the egg during incubation, and conse- quently the amount of respiratory matter in its food must be in proportion to the increased consumption of oxygen. We may, perhaps, conclude from this, that the proportion of non-nitrogenous to plastic matter in eggs, is the minimum required by warm-blooded animals in their food ; the smallest proportion consistent with life under any circumstances. Milk-sugar and grape-sugar (which latter is formed from starch and cane-sugar in the digestive process), disappears in the blood with extreme rapidity, so that it has only in very few cases been possible to detect them in the blood. In like manner the fat consumed by a man or beast, whose weight does not change from day to day, entirely disappears. If more fat be added to the food of animals than corre- sponds to the inhaled oxygen, the excess is stored in cells, the walls of which consist of the same substance which forms the chief part of membranes and of bones. If the constituents 398 LETTERS ON CHEMISTRY. of the blood or of the food do not suffice for the formation of these cells, the substance of the muscles is employed for that purpose ; the animal gains in fat, and loses in muscular flesh. Beyond this point, again as happens in geese when fattened in a certain way the fat accumulates in the blood, causing disease, and finally death. (Persoz, in the Ann. de Chim. et de Phys. ; Nouv. Se>ie, XIV., 417.) If animals receive in their food a larger amount both of plastic and of respiratory matter (not fat) than is required for the support of their vital and respiratory processes, the plastic matters accumulate in the form of flesh and cellular tissue; while the others (sugar, milk-sugar, &c.) are converted into fat. This important fact namely, that the sugar formed in digestion from the starch of grain, potatoes, and leguminous seeds, is converted into fat when sufficient materials are supplied for the formation of cells, has been placed beyond a doubt by the experiments of Persoz and Boussingault. (See the Memoir last referred to, p. 419.) It has been already pointed out, that grape-sugar and milk-sugar have a composition analogous to carbonic acid. For one equivalent of carbon, carbonic acid contains two equivalents of oxygen ; grape-sugar and milk-sugar, for one equivalent of carbon, also contain two equivalents namely, one equivalent of oxygen, and, in place of the second equi- valent of oxygen, one equivalent of hydrogen. The con- version of sugar into carbonic acid ultimately consists, therefore, in a formation of water, or at least depends on that formation. The oxygen absorbed in respiration com- bines with the hydrogen of the sugar to form water, and when the hydrogen has been replaced by its equivalent of oxygen, the sugar at once passes back into carbonic acid. On this view, no true combustion of carbon occurs in the living body ; but the carbonic acid is formed by a process of substitution in this case one of decay, or slow oxidation, from a body rich in hydrogen, the hydrogen of which is oxidised and removed, and replaced by one or more equiva- lents of oxygen. PRODUCTION OF FAT. 899 The proximate condition of the formation of fat, or of the deposition of the combustible respiratory materials in the cellular tissue of the body, is a deficiency of oxygen. Were the supply of oxygen sufficient to convert the carbon and hydrogen of these substances into carbonic acid and water, these elements would be expelled, and no part of them would be accumulated in the body in the form of fat. A knowledge of the phenomena of fermentation, allows us to penetrate into the processes by which, in the animal body, the highly oxidised sugar is converted into fat, a body containing so little oxygen. Fermentation, in its results, is always a resolution or splitting up of a complex atom into two, one of which con- tains most of the oxygen, the other very little. In the alcoholic fermentation of sugar, while two-thirds of the oxygen are separated as carbonic acid, we obtain the easily inflammable and combustible alcohol, much less rich in oxygen. From the same sugar, by the separation of two oxidised products, carbonic acid and a certain amount of water, we obtain the oil of potato spirit (fusel oil, oil of grain), which approaches still more closely to fat oils in its physical characters ; and when the separation of carbonic acid is accompanied by that of a certain amount of hydrogen, we obtain butyric acid, a true oily acid. The origin of fat in the animal organism, pre-supposes precisely similar conditions ; we regard the formation of fat as the result of two processes, which occur simultaneously. One is an imperfect process of oxidation (of decay or erema- causis), by which a certain amount of hydrogen is separated from the elements of sugar ; the other, a process of splitting up a complex atom (of fermentation), by which a certain amount of oxygen is separated from the elements of sugar, in the form of carbonic acid. (See Animal Chemistry, p. 102.) The opinion that this transformation is determined by a ferment in the liver, which behaves towards sugar, in the production of fat, as saliva does towards starch, or as the lining membrane of the stomach does in digestion, and 400 LETTERS ON CHEMISTRY. that hence the liver is the seat of this process, is not destitute of probability, but requires to be more accurately demonstrated.* All substances which serve as food to men and animals contain always and under all circumstances a certain amount of fatty matter, or of bodies analogous to fats in their characters. The flesh of wild animals, however, is usually devoid of fat. In all those cases in which the weight of the body and the quantity of fat remain unaltered, we may therefore conclude that fat, sugar, and starch, are exclusively employed in supporting respiration, and that the latter are not em- ployed to produce fat. The formation of fat, beyond the limit of the quantity required by the body for the promotion of the organising processes, or the deposition of fat in the fattening of animals, is always the result of a misproportion between the respiratory and nutritive processes, and rather a sign of a morbid than of a normal healthy state. Nature has destined the non-nitrogenous bodies for the support of the animal heat, and we find all food most wisely com- pounded for this object. Nature has given to the organism the power to reduce every disturbance of the vital functions to a minimum of hurtful effect by storing up the excess of combustible elements. These elements, in the form of fat, being separated from the blood, and deposited externally to the circulatory system, in a form well adapted to future use, the blood maintains its normal composition. By the separa- tion of the combustible elements from the blood, a deficiency in that fluid of the oxygen indispensably necessary for other purposes is prevented, and the equilibrium preserved. * When a fresh calFs liver is cut in pieces, covered with water, and exposed to a temperature of from 98 '6 to 104 F., a remarkable fermen- tation begins after four or five hours.' The liver becomes covered with a number of gas-bubbles, chiefly formed of hydrogen. Each bubble, as it rises, may be kindled at the surface. In an open vessel, during the first hours of this fermentation, no putrid smell is observed. It is hence obvious that the liver contains a substance which, in a certain state of decom- position, becomes a ferment powerful enough to decompose water, the oxygen of which is taken up by the elements of the ferment. RESPIRATORY MATERIALS. 401 The fact that the plastic substances also, in certain pro- cesses of decomposition, as in putrefaction, are resolved almost entirely into ammonia and oily acids (butyric and valerianic acids) renders conceivable the opinion, that these substances may serve, under certain circumstances, for the production of fat in the animal organism. It appears at all events significant in regard to the formation of fat in the living body, that the production of fatty or oily acids, such as butyric acid, from non-nitrogenous matter, out of the body, is only effected by ferments, the elements of which are themselves in the condition of butyric fermentation ; and it is not altogether improbable, that in the living body also, a similar relation exists between plastic and non-nitrogenous bodies, in reference to the formation of fat. Equal weights of the different respiratory materials contain very unequal quantities of combustible elements ; as may be seen by the following table : Grape-Sugar. Cane-Sugar. Starch. Alcohol. Carbon . . 40'00 42-10 44'44 52-18 Hydrogen . . 6 -66 6*43 6 -17 13 '04 Oxygen . . 53 '34 51 '47 49 '39 34'78 100-00 100-00 100-00 100-00 The amount of carbon and hydrogen in fatty bodies is much greater. Olive oil, for example, contains 77 per cent., hog's lard and mutton suet 79 per cent, of carbon, and 11 or 12 per cent, of hydrogen. All other fats have a composition intermediate between these two. Now, since the power of these substances to develope heat by their combination with oxygen, depends on the proportion of combustible elements, contained in equal weights, and since the amount of the oxygen required for their complete combustion, rises with that of the carbon and hydrogen, it is easy to calculate, approximately, their relative values as producers of heat or supporters of respiration. The following table contains the different respiratory materials, arranged in a series ; the numbers express how much of each is required to convert a given weight of oxygen into carbonic acid and water ; or, approximately, how much of each must be taken 402 LETTERS ON CHEMISTRY. in the food, in order, with the same consumption of oxygen, to keep the body at the same temperature during equal times : 100 Fat. 240 Starch. 249 Cane-sugar. 263 Grape-sugar (dry), Milk-sugar (cryst.) 266 Spirits, of 50 per cent, of Alcohol. 770 Fresh lean flesh. Hence it appears, that 1 Ib. of fat performs the same amount of work, in respect to the respiratory process, as 2% Ibs. of starch, or 2 J Ibs. of cane-sugar, or 7-^j Ib. of muscular flesh. Fat is the best, muscular fibre appears the worst of all respiratory materials. In calculating the respiratory value of muscle, it has been assumed, that the flesh consumed as food is ultimately transformed into urea, carbonic acid, and water. This supposition is only true in part for, in the urine and the intestinal secretions, other compounds of nitrogen are excreted, which contain a much larger proportion of carbon than urea. At all events, that portion of carbon which is separated in the form of compounds of nitrogen takes but a very insignificant share in the production of the heat of the body. The plastic matters in the food contain nitrogen and carbon in the proportion of 1 equivalent to 8. If no other nitro- genous body than urea were contained in the urine, urine would be found to yield, for 1 equivalent of nitrogen, only 1 equivalent of carbon. But, in his experiments on the nutri- tive process in the horse and cow, Boussingault found, in the urine of the horse, nitrogen and carbon in the proportion of 1 equivalent to 6 -6 equivalents ; and in that of the cow, 1 equivalent to 16. (Ann. de Chim. et de Phys. LXXI. 122.) In special experiments made on this point in my laboratory, there were found in the urine of the horse, for 1 equivalent of nitrogen, 5 equivalents ; in that of the cow, 8 equivalents ; in human urine, 1*8 equivalents of carbon. The excreta of a pig, liquid and solid taken together, the food having been potatoes, contained nitrogen and carbon in the proportion of RESPIRATORY MATERIALS. 403 1 to 10 equivalents. These facts might, perhaps, justify the conclusion that the combustible elements of the plastic mat- ters in the food, in many animals, are either not sent out from the body through the skin and lungs at all, or are so only to a very small extent, and that we can hardly assign to them any share in the production of the animal heat. I) D 2 401 LETTERS ON CHEMISTRY. LETTER XXXI. Essential Importance of the Mineral or Incombustible Elements of Food The Ashes of Vegetable Food are the same as those of Blood and Flesh The Blood invariably Alkaline, and this is a Condition essential to its Fluidity and to all its Functions The Alkaline Salt is the Phosphate of Soda, while in all the Tissues, and in the Juice of Flesh, the Phos- phoric Acid is in excess ; but in Herbivora the Phosphate is partly replaced by another Alkaline Salt, the Carbonate of Soda A know- ledge of the Ashes of the Food enables us to predict the precise Salts in the Blood, the Urine, and the solid Excreta The soluble Salts are found in the Urine ; the insoluble, in the Fseces Relations of the Salts of the Blood to the Secretions and Excretions Table of the Urine with Animal Food and with Vegetable Food In Disease, the Analysis of the Ashes of Urine and Blood will become a valuable aid to the Physician The Alkalinity of the Blood essential to the Oxidation of the Respira- tory Food, and of the Products of the change of Matter, such as Uric Acid, which, although formed, never reaches the Kidneys in the Her- bivora, whose Urine is Alkaline Salts of Vegetable Acids, in the Body, become Carbonates The Excretion of the free Acids in the Urine of Carnivora is essential to preserve the Alkalinity of their Blood The Nature of the Blood and of the Urine may be changed by Diet Iron in the Food, essential to the Blood Functions of Common Salt in the Food and in the Blood Experiments on its use, and suggestions on this Point Endosmosis of Saline Solutions Effects of drinking Spring Water, and Solution of Salt Salt a necessary of Life. IN the two preceding letters there has been ascribed to certain constituents of seeds, roots, tubers, herbs, fruits, and flesh, the power of supporting the processes of nutrition and respiration ; and it will appear as a very striking contradic- tion, when it is stated, that no one of these substances, by itself, neither caseine alone," nor the substance of muscular fibre, the albumen of eggs or of the blood, nor the corre- sponding vegetable products, are able to support the plastic or formative processes ; that neither starch, sugar, nor fat can sustain the process of respiration. Nay, it may excite still greater astonishment to add, that these substances, even MINERAL CONSTITUENTS OF FOOD. 405 when mixed, no matter in what proportions, are destitute of the property of digestibility, without the presence of certain other substances ; so much so, indeed, that if these other conditions be excluded, the above-named compounds are utterly unable to effect the continuance of life and of the vital phenomena. In the numerous experiments of physiologists and chemists, in which the attempt was made to feed animals with these substances, alone or mixed together, all the animals died, after a shorter or longer time, with the appearances which accompany starvation. Even after a few days, the utmost tortures of hunger were found insufficient to induce these animals to take the food offered to them ; since the experi- ence of these few days and their instinct, at first deceived, told them that the introduction of this food into their stomachs was as truly indifferent or useless for the purposes of nutrition, as the eating of stones. On the other hand it is a fact, confirmed by the experience of thousands of years, that flesh and bread, either separately or mixed together, as well as the milk of animals, suffice to support life in full vigour, without the necesity of adding any other substance whatever. And hence it follows, necessarily, that these articles of food, flesh, bread, and milk, and likewise the plants, or parts of plants, consumed by the herbivorous animal, must contain, and in the due proportion, those other conditions, the presence and co- operation of which is indispensably necessary for the pro- cesses of digestion and nutrition. These necessary matters, essential to the organic processes, by the presence of which the plastic constituents of food and the respiratory materials acquire those properties which render them fit and proper for the support of life, are the incombustible constituents, or the salts of the blood. The incombustible parts of the blood of all animals are of the same nature and quality. Leaving out of view such as are accidental or variable, the blood, at all times and under all circumstances, contains certain quantities of Phosphoric Acid, of Alkalies (potash and soda), Alkaline 406 LETTERS ON CHEMISTRY. Earths (lime, magnesia), Iron (oxidised), and Common Salt (chloride of sodium). All these matters, before they became parts of the blood, were constituents of the food of man or of the fodder of animals. If, then, it be true, that these substances take or have taken a necessary and determined part in converting the constituents of food into constituents of the body, it follows, that no kind of food can sustain life, in which these substances are wanting ; that all kinds of food for man or animals, which possess full nutritive power, must contain these bodies in the proportions adapted to the formation of blood ; and that we can deprive the food of its sanguine properties, if we deprive it of these conditions, indispensable to those peculiar properties. Analytical chemistry has furnished the strictest proofs of the justice of these conclusions, by showing, that turnips, potatoes, and the herbs eaten by the herbivora, contain the same incombustible constituents as their blood, and very nearly in the same proportion.* The constituents of the ash of the blood of graminivorous animals are identical with those of the ash of grain ; the incombustible constituents of the blood of men and of such animals as consume a mixed food, are the constituents of the ashes of bread, flesh, and vegetables. The carnivorous animal contains, in its blood, the constituents of the ash of flesh, f Ashes of Sheep's blood. Ox blood. White cabbage. White turnips. Potatoes. Dr Verdeil. Dr. Stolzel. Stammer Stammer. Dr. Griepenkerl. * Phosphoric acid 14*80 14-043 137 14-18 16-83 Alkalies . . . 5579 59-97 49-45 52-00 55-44 Alkaline earths . 4'87 3'64 14*08 13-58 6-74 Carbonic acid . 19'47 18'85 12'42 8'03 12-00 The ashes are calculated in 100 parts, after deducting the common salt and iron, the loss or deficiency in 100 parts consists of accidental constitu- ents, as sulphuric acid, silica, &c. Ashes of Dog's blood. Ox flesh. Pig's blood Dr. Verdeil.* Dr. Stolzel, f Dr. Strecker. t Phosphoric acid . . . 36-82 42-03 36*5 Alkalies 55*24 43 -95 49 '8 Alkaline earths . . . 2'07 6-17 3*8 Silicic acid, and Sulphuric acid . 5 '87 7'85 9*9 Fed with flesh. f Fed with peas and potatoes. ; BLOOD REQUIRES TO BE ALKALINE. 407 The blood of all animals has invariably an alkaline character, arising from the presence of a free, fixed alkali. All articles of food which alone, as bread and flesh, or when mixed with vegetables, are capable of sustaining the process of sanguification and nutrition, contain carbonic acid or phosphoric acid, and alkalies, the latter two in such proportion that, if we suppose them dissolved, the alkalies invariably predominate. That this free alkali plays an indispensable part in the process of sanguification and in the functions of the blood, is plainly seen in the before-mentioned experiments of the French academicians; for the dogs, which, when fed on animal fibrine, on caseine,* or on flesh boiled and pressed out, died of starvation, received, in these forms of food, a quantity of alkalies altogether insufficient for sanguification. Flesh, from which the fluids have been pressed out, contains phosphoric acid and alkalies in such a proportion, that if we suppose them dissolved, the acid and not the alkali predominates. If both could become at the same time constituents of the blood, the blood would have an acid, and not an alkaline reaction. But, on a closer examination, an acid state of the blood appears to be utterly irreconcileable with the functions which it has to perform in the nutritive and respiratory processes. The free alkali gives to the blood a number of very remark- able properties. By its means the chief constituents of the blood are kept in their fluid state ; the extreme facility with which the blood moves through the minutest vessels, is due to the small degree of permeability of the walls of these vessels for the alkaline fluid. The free alkali acts as a Ashes of Peas. Fowl's blood. Rye. ( Will and Dr. Henneberg. Will and Fresenius. Fresenius. Phosphoric acid . 34-01 47-26 47-29 Alkalies .... . 45-52 48.41 37-21 Alkaline earths . 9-61 2-22 11-60 Silicic acid, and Sulphuric acid . 10-86 2-11 3-90 Cheese made with rennet (Gruyere), contains, according to the anylysis of Johnston, for 45 parts of phosphoric acid, only 13--18 of alka- lies, and 41 of lime and magnesia. 408 LETTERS ON CHEMISTRY. resistance to many causes, which, in the absence of the alkali, would coagulate the albumen. The more alkali the blood contains, the higher is the temperature at which its albumen coagulates ; and with a certain amount of alkali the blood is no longer coagulated by heat at all. On the alkali depends a remarkable property of the blood, that of dissolving the oxides of iron, which are ingredients of the colouring matter of the blood, as well as other metallic oxides, so as to form perfectly transparent solutions. The free alkali plays a peculiarly important part in the processes of respiration and secretion, which we shall explain more minutely in considering the urine. The significance and importance of phosphoric acid in the vital process is obvious, when we remember that this acid is a never-failing ingredient of all the organised structures of the animal body. The substance of muscular fibre, the fibrine of blood, the pulmonary tissues, the liver and the kidneys contain a certain amount of phosphoric acid in chemical combination. The ashes or incombustible ingre- dients of the fluids of the flesh are, in all animals, of the same nature and quality. They consist of alkaline phosphates, phosphate of lime, and phosphate of magnesia. The bones of the vertebrata contain more than half their weight of the phosphates of lime and magnesia. The substance of the brain and the nerves contain a phosphoric acid, coupled with a fat or with a fatty acid, the phosphoric acid being, partly, in combination with an alkali.* The phosphoric acid contained in these tissues is derived from the blood. The blood contains, under all circumstances, a certain amount of phosphoric acid. In the present state of science, it is not yet possible to * Ashea of Free Phosphoric Alkaline 'Earthy Acid. Phosphates. Phosphates. Horse flesh (Dr. Weber) . . 2'62 80-96 16-42 Ox flesh, washed out (Dr. Keller) . 17'23 48 '06 26 -26 Ox brain (Dr. Breed) . . . 16'57 74-41 9'02 Yolk of Egg (Dr. Polek) . . . 3674 27'25 34-70 The phosphates are calculated according to the formula P 5 , 2 M 0. The horse flesh was from the fore leg of a lean horse, entirely freed from blood by washing out the brachial artery by injection. PHOSPHORIC ACID INDISPENSABLE. 409 express a decided opinion as to the mode of action of the phosphoric acid in the organic process, and we must for the present be satisfied with deducing, from its constant presence in all the juices and organised tissues of the body, the conclusion that it is indispensable for the vital operations.* If we imagine the animal organism to be divided into two parts, observation shows that the changes going on in these are effected in one by the co-operation of a predominant alkali, in the other by that of a free acid. All organised solid parts contain alkaline bases and phosphoric acid, in such a proportion that if we suppose them combined, the phosphoric acid predominates. (See note p. 408.) The blood contains an excess of fixed alkali ; but the lymph and chyle also have an alkaline reaction ; and it * Some facts seem to favour the opinion, that the phosphoric acid, and the acid earthy phosphates can form true chemical compounds with, albumen, and with the substance of the membranes ; and that many pe^u- liarities of the latter, as, for example, their insolubility in water and in alkaline fluids, depend on this cause. If, for example, we add to milk, cautiously, a diluted acid, till the alkaline re-action disappears, and then heat it to boiling, it now coagulates like white of egg. The caseine, thus precipitated, differs very essentially from pure caseine, by its insolubility in alkaline fluids. The caserne coagulated from milk by rennet, has the same characters. Both are compounds of caseine with the phosphates of the alkaline earths (lime and magnesia) ; or if we consider the so-called pure caseine as a complex acid containing phosphoric acid, the insoluble caseine is the lime or magnesia salt of this acid. The phosphate of lime existing in common gelatine in chemical combination, has a most decided share in giving to that substance the property of forming a jelly. It is well known that, by continued boiling of animal skins and bones there is obtained a solution of glue, which, on cooling, forms a stiff jelly. But if the solution of this jelly, alone, or with the addition of alkali, be boiled for a still longer time, it loses the property of gelatinising, and at the same time phosphate of lime is separated. The very peculiar behaviour of the fibrine of blood in contact with hydrochloric acid, has been pointed out at p. 276. When the fibrine, which in. the dilute acid liquid, has swelled up to a jelly, is heated to boil- ing with the liquid, it dissolves, forming a solution that may be filtered, in which phosphoric acid and lime may now be detected by re-agents ; and by the separation of these two bodies from the organic ingredient, the fibrine of blood, exactly like gelatine becomes soluble in cold water. It is probable, that the coagulation of albumen, of the serum of blood, and of eggs depends on the separation of alkali, and the formation of a new com- pound of albumen with phosphoric acid and lime, insoluble in the cold, in water, dilute acids, and alkalies. 410 LETTERS ON CHEMISTRY. would appear to follow, from this, that on the alkali depend, not only certain properties, but also the formation and pro- duction of the blood. The formation and production of the organised structures cannot be imagined without an excess of phosphoric acid. A similar contrast is observed in the egg. The white of the hen's egg contains, among its incombustible constituents, an excess of alkali ; the yolk contains free phosphoric acid. (See note, p. 408.) When we compare the ashes of the blood of herbivorous, graminivorous, and carnivorous animals together, we observe, in the proportion of the alkalies to the phosphoric acid, most extraordinary differences. The blood of the pig and of the dog contains 36 per cent., that of fowl above 40 per cent., that of oxen and sheep not more than from 14 to 16 per cent, of phosphoric acid. (See note, p. 406.) How, it may be asked, are such marked differences to be reconciled with the constant functions of the blood 1 If the incombustible ingredients of ox blood, in the proportions therein found, be necessary for the vital changes in the body of the ox, how can we explain the fact, that the blood of the pig or dog, with a composition so different, can serve the same purposes ; which purposes we see attained in them exactly in the same way as in the body of the animals fed on grass? In fact, analysis can discover no difference in the composition of the organs or of those parts of the body external to the blood vessels, as far as concerns these incom- bustible constituents. While the ingredients of the ashes of the blood of herbivorous and carnivorous animals differ to such an extent, that we can at once distinguish them by analysis, merely by observing the amount of phosphoric acid in each, it is utterly impossible, by analysing the incom- bustible ingredients of the flesh, to distinguish that of the ox from that of the pig or dog, or to say, which ashes have been obtained from the flesh of the carnivorous or of the herbi- vorous animal. The ashes of the juice of flesh of the ox, calf, sheep, pig, dog, marten, fox, and fishes, always contain FUNCTIONS OF PHOSPHORIC ACID. 411 phosphoric acid and alkalies in the same proportion as the pyrophosphates (bibasic phosphates). Those parts of the muscular substance, of the cellular tissue, of membranes, of the pulmonary and hepatic issues, which are insoluble in cold water, always contain an excess of phosphoric acid, so that, in their incineration, certain quantities of metaphos- phates (monobasic phosphates) are always formed. But if the constituent parts of the organs and of all the tissues of the herbivora are, in regard to their incombustible elements, of the same composition as those of the carnivora ; if the variation or increase of the amount of phosphoric acid in the blood does not alter nor increase the amount of this acid in the fluids of the muscular system and in the tissues, and its diminution in the blood does not diminish its amount in those other parts, it follows, of course, that the increase of phosphoric acid in the blood has no influence whatever on the process of formation of the blood itself. The blood carries to all parts of the body the necessary phosphoric acid, and must therefore always contain a certain amount of that acid ; but the phosphoric acid plays no part in sanguification or in the functions of the blood, because its properties as an acid entirely disappear in the excess of alkali in the blood. In the blood of animals belonging to different classes in respect to their food, we observe a variation in two ingredi- ents, namely, phosphoric acid and carbonic acid ; but this difference in composition is without any influence on the properties of the blood, which retains its alkaline character. In the blood of the herbivora we find the alkali in part com- bined with carbonic acid ; in that of the carnivora we find this carbonic acid represented and replaced by phosphoric acid, without any alteration of the character or of the functions of the blood.* * Ashes of Human blood. Calves' blood. Sheep's blood. Phosphoric acid . . . 31787 20-145 14-806 Alkalies and Alkaline earths . 58'993 66'578 60*576 Carbonic acid . . . 3783 9.848 19-474 These analyses, by Dr. Verdeil, show, that as the amount of phosphoric 412 LETTERS ON CHEMISTRY. This is again one of the numberless facts, which fill with inexpressible admiration the soul of the observer of natural arrangements ; namely, that an alkaline phosphate exhibits towards carbonic acid the same comportment, as a neutral alkaline carbonate does. Contrary to all known laws, it appears to the chemist like a miracle, that two acids, a gaseous one and a fixed one, one of the weakest and one of the strongest, which of all acids differ most in composition, can form, with the alkalies found in the blood, compounds of the same chemical character. Phosphate of soda has an alkaline taste and re-action, like the carbonate ; and its solu- tion in presence of free carbonic acid takes up as much of that acid as the carbonate of soda does, and like it, only more easily, gives it off by agitation with air, in vacua, or by evaporation, without losing its power of again absorbing the carbonic acid. It is easy from this to understand, that if certain functions belong to the blood, which depend on its chemical character, on its alkaline quality, that, for these objects, a change of the acid combined with the alkali, the replacement of the carbonic acid of the carbonated alkali by phosphoric acid, and vice versd, has no influence, because it causes no altera- tion of the essential properties of the blood. The blood is the common soil, from which all parts of the living body are developed in all animals in the same way, and with the same unchangeable composition ; but it is at the same time the source of animal heat, and its canals are the passages through which the matters unfit for the vital changes, and the worn out parts (the products of the change of matter) are carried to the organs of secretion and thus expelled from the body. For these purposes, the blood must possess all the neces- sary conditions. In the combustible ingredients it has the acid diminishes, that of carbonic acid increases. The difference in the quantity of alkalies is, in part, only apparent, for they consist of potash and soda, of which we know that they replace each other in very unequal weights. Common salt and iron have been deducted. What is wanting of 100 parts is accidental ingredients. FOOD AFFECTS THE COMPOSITION OF BLOOD. 413 matters which are to become the organs of vital activity, or are to serve for the production of heat ; and in the incom- bustible constituents it has the indispensable conditions of its efficiency in these respects. In the formative process we see the phosphoric acid (and besides it no other fixed or incombustible acid) perform a defined part. The processes of sanguification, of the production of heat and of secretion, are carried on under the influence of a predominating alkali. The partial replacement of phosphoric acid by carbonic acid, and vice versd, which may take place in the blood, without alteration of its properties, explains how it happens that the change from vegetable to animal diet, causes no change appreciable in ordinary circumstances in the body of man, although, by that change of diet, an essential difference in the composition of his blood as regards the incombustible constituents is produced. We can now with the greatest ease and certainty deter- mine beforehand, from the known composition of the ashes of the food, the nature and quality of the incombustible constituents of the blood ; since we know that those of the blood are derived from the food, and that both are identical. When the food consists of bread or flesh, which leave in their ashes no carbonates, but only phosphates, the blood contains only phosphates ; if we add to the bread or flesh, potatoes or green vegetables, the blood acquires a certain amount of alkaline carbonates ; if we replace the bread and flesh entirely by fruits, roots, or green vegetables, the blood of man acquires the composition and quality of that of the ox or sheep. But although the exchange of phosphoric and carbonic acids in the blood, when the diet is changed from animal to vegetable, appears to have no influence on the processes of sanguification, nutrition, and production of heat, yet the process of secretion is very essentially modified in its form by this exchange. It is evident, that in the normal state of health, in which the weight of the body of man or animals does not change, 414 LETTERS ON CHEMISTRY. the alkalies, alkaline earths, phosphoric acid, and oxide of iron, received in the food, do not accumulate in the body, but are daily expelled in the same proportion as they are introduced in the food. We know with perfect certainty, that this excretion is effected by two organs of secretion, namely, the kidneys and the intestinal canal. The constituents of the ashes of the urine and of the solid excreta are, in the normal state, equal in weight to the incombustible ingredients in the food ; it is only when the individual increases in organised parts, that is, in weight, that certain quantities of phosphates are retained in the new parts as belonging to their composition. A knowledge of the incombustible constituents of the food of healthy men, or of the fodder of animals, enables us to conclude with mathematical certainty, from the nature of the food, as to that of the urine and solid excreta, and to, predict what must be the reaction of the urine, and in what proportion these constituents are to be found in the urine and faeces. The incombustible constituents of bread, flesh, seeds, roots, tubers, herbs, and fruits, are, in all these articles of food, of the same nature and quality, but in very different proportions. They may be easily distinguished from one another by their properties. The alkalies (potash, soda) are, both alone, and in combi- nation with phosphoric, sulphuric, and carbonic acids, easily soluble in water. The alkaline earths (lime, magnesia) are in their neutral compounds with phosphoric and carbonic acids, insoluble in water. The carbonates of the alkaline earths, on the other hand, dissolve in water containing' free carbonic acid ; the earthy phosphates in water containing free phosphoric acid, or any free numeral or organic acid. The substances above-named are the never-failing con- stituents of the ashes of the food of man, or of the fodder of animals. Phosphoric acid, the alkalies, and the alkaline ASHES OF FOOD. 415 earths (with peroxide of iron, and, in fodder, silicic add,) are present, as such, before combustion. Sulphuric and carbonic acids are products of the combustion of sulphur and carbon. If we suppose these ashes to be acted on by water, they are divided into two parts. The soluble matters are taken up by the water ; the insoluble are left in the residue. If the ash contain phosphoric acid and sulphuric acid (and silicic acid) in such a proportion that, taken together, they suffice to neutralise the alkalies and alkaline earths which are present, we obtain IN SOLUTION. Phosphoric acid 1 Potash, Sulphuric acid J Soda. IN THE RESIDUE (undissolved). Phosphoric j Lime, acid, > Magnesia, Silicic acid, j Peroxide of iron. If the quantity of alkaline earths present be sufficient to combine with all the phosphoric acid in the ash ; if, there- fore, there be a want of phosphoric acid to combine with the alkalies, all the phosphoric acid is found in the insoluble residue, and we obtain IN SOLUTION. Carbonic acid, ) Potash, Sulphuric acid. ) Soda. IN THE RESIDUE. Phosphoric acid, Carbonic acid, Silicic acid. Lime, Magnesia, Peroxide of In the living body the food undergoes precisely the same change as if we had burnt it in a furnace, and in regard to the incombustible constituents a perfectly similar division takes place. In the process of digestion those constituents of food or of fodder, whether combustible or incombustible, which are soluble in alkaline or slightly acid liquids, are dissolved, and taken into the circulation. By the action of the oxygen absorbed in respiration, the combustible portions are ulti- mately burnt that is, oxidised. The non-nitrogenous bodies are converted into carbonic acid and water, the plastic substances into uric acid, hippuric acid, and urea, their sulphur into sulphuric acid. 416 LETTERS ON" CHEMISTRY. By means of the organs of secretion, the kidneys and the intestinal canal, the above named products of the organic process of combustion and the constituents of the ashes of the food, in so far as they are unfit for further use in the vital operations, are expelled from the organism. The urine contains the soluble, the faeces the insoluble constituents, of the ashes of the food. The alkalies, as well as the products of the change of matter, which form with them soluble compounds, are contained in the urine ; the rest are found in the faeces. When the food has been bread or flesh, the ashes of which contain only phosphates, the urine contains the alkalies in the form of alkaline phosphates. If the food has consisted of roots, green vegetables, and fruits, the ashes of which contain, as soluble salts, only alkaline carbonates, the urine contains alkaline carbonates. The products of the organic process of combustion, formed in the body sulphuric acid, uric acid, hippuric acid have a powerful attraction for the alkalies. When these acids are added to a solution of phosphate of soda (P 5 , 2 M 0, H 0), or of carbonate of soda they share the alkali with the phos- phoric or carbonic acid ; by removing from the salts of these acids a part of the base, they set free a certain amount of phosphoric or of carbonic acid. The very same thing happens in the separation of the urine from the blood. The alkalies hold in chemical combination all the acids present in the blood, or formed in that fluid. The urine of man and animals always contains a free acid, or an acid salt. During the separation of the urine from the blood, in con- sequence of the addition of sulphuric, hippuric, or uric acid, to the alkaline phosphate, a part of the alkali is removed from that salt, a corresponding portion of its phosphoric acid is set free, the salt, originally of an alkaline reaction, becomes neutral or acquires an acid reaction. If the soluble parts, of the ash of the fodder consisted of alkaline carbonates, these pass out of the body in the urine in the form of bicarbonates, combining with the free carbonic acid of the blood. SALTS FOUND IN URINE. 417 But since a liquid, which is rendered acid by free phos- phoric acid or by a fixed acid, has the property of dissolving the phosphates of lime and magnesia, and a liquid rendered acid by free carbonic acid has a similar power of dissolving the carbonates of lime and magnesia, the urine which is acid from phosphoric acid, always contains earthy phosphates ; while that which is acid from carbonic acid, always contains earthy carbonates in solution. With food consisting of Flesh, Bread, Peas, Beans, or Lentils, the Urine contains : Free Phosphoric acid. . ,, . ,. of the Alkalies " Phosphates of Phosphates, Sulphates. Urates, Hippurates, This urine has a permanent add reaction. Acid urine contains (usu- ally) uric acid. With Vegetable food, Hay,. Clover, Tur- nips, Potatoes, fruit, &c., the Urine contains : Free Carbonic acid. Carbonates of Carbonates, Hippurates, > of the Alkalies. Sulphates, This urine has a transient acid reaction ; a permanent alkaline re- action. Alkaline urine contains no phosphoric acid, and no uric acid. From these researches it clearly appears, that the acid, alkaline, or neutral state of the urine of healthy men or animals, as well as the presence in the urine of phosphoric and uric acids, of earthy phosphates or earthy carbonates, ultimately depends on the nature and quality of the consti- tuents of the ashes of the food or fodder. The urine of a pig fed on potatoes, which is alkaline, becomes acid as soon as the animal receives corn or peas in its fodder. In like manner, the urine of man loses its usual acid reaction, and becomes neutral or alkaline, when juicy fruits, cherries, apples, potatoes, roots, and green vegetables are added to his food in a certain proportion. The salts of the urine are separated from the blood by the kidneys; before this separation they formed part of the blood. The analysis of the urine enables us to compare its incom- bustible constituents with those of the blood ; and observa- tion shows, that in regard to the proportion of soluble salts with alkaline base, there is hardly any difference between E is 418 LETTERS ON CHEMISTRY. them.* If we incinerate the blood of a healthy person, and also his urine, and lixiviate the ashes with water, the soluble salts of the blood ash are in nature the same as those of the urine ; and it is extremely probable that, in regard to their relative proportions also, a constant relation prevails. We have, therefore, every reason to hope, that we may be enabled, by a very simple chemical operation, to reason back- wards from the urine to definite conclusions as to the quality and composition of the blood ; and it will require only a small number of comparative examinations of the urine and of ashes of the blood in different diseases, to enrich pathology with the means of research invaluable from the certainty of its indications ; by the aid of which the physician may ascertain the changes occurring in the composition of the blood in disease, and may judge of their influence on the functions of the blood, and consequently on the most important vital processes. It does not require much chemical knowledge to perceive that the discovery of the law which regulates the dependence of the quality and functions of the blood on the nature and amount of its incombustible constituents, is the foundation- stone of medicine and physiology; and that it is utterly absurd even to dream of a rational science of medicine, before we have laid this foundation-stone, on which must rest the solution of all questions concerning the animal economy. It is impossible for the chemist not to acknowledge, that the alkaline quality of the blood is one of the first and most important conditions of the organic process of combustion, of the production of animal heat, and of the change of matter in the body. A number of organic compounds acquire, by contact with, * Analysis of human urine, after deducting the common salt : Phosphoric Alkaline Sulphuric Acid, Acid. Alkalies. iiarths. Silicic Acid. Urine (Porter), Giessen 34'24 47'76f 7'62 12-38. Urine (Fleitmann), Berlin 34 '03 48 '03 9 '02 8 '92 t Here 4'06 parts of soda have beeu reduced to potash and calculated in that form. INFLUENCE OF THE ALKALIES. 419 or in presence of a free alkali, the power of combining with oxygen (of burning), which, alone, they do not at all possess at the ordinary temperature of the air, or at the temperature of the body. (Chevreul.) The influence of alkalies in this way is most strikingly seen in such substances as are coloured, and become decolourised under these circumstances, or in such as are colourless, and become coloured as they are destroyed. Carmine, the most durable organic colouring matter known to us, the colouring matters of Logwood and Brazil wood, and the colouring matter of the blood, dissolve in solution of potash, and may be preserved for months unchanged. But as soon as air or oxygen is admitted to these solutions, oxygen is rapidly absorbed, and these colour- ing matters are destroyed. (Chevreul.) The colourless solution of pyrogallic acid, or that of gallic acid, when mixed with excess of alkali, becomes, when oxygen is admitted (see p. 357), dark red, and is destroyed in a few minutes. Even alcohol is oxidised, when it contains free alkali, and is exposed to air at the ordinary tempera- ture, and becomes brown. Milk-sugar, and grape-sugar, in presence of a free alkali, and with the aid of a gentle heat, deprive even metallic oxides of their oxygen. (See p. 381.) The alkalies exert a precisely similar action in the blood ; they promote and increase the combustibility of the respi- ratory matters. This influence of the alkalies is shown in a decisive man- ner, in the effects produced on the salts of organic acid in the circulation. It has long been observed, that after eating juicy fruits, cherries, strawberries, apples, &c., the urine becomes alkaline. All these fruits, as well as the juices of edible roots, tubers, and green vegetables, contain these alkalies in the form of salts of the organic acids ; usually as malates (all kernel fruits, pine-apple) ; citrates (stone fruits, currants, potatoes) ; tartrates (grapes). It has been shown by Gilbert Blane and by Wohler, that the pure salts, malates, citrates, tartrates, &c., of the alkalies, when taken internally, behave exactly as the salts in the juices of these fruits and E E 2 420 LETTERS ON CHEMISTRY. roots. Citrate, tartrate, malate, and acetate of potash, whether given by the mouth, or in enemata, appear in the urine in the form of carbonate of potash. The acids of these salts, introduced into the blood in the form of neutral or acid salts, are there burned (oxidised) as effectually as in the most perfect apparatus of combus- tion. The alkaline carbonates which predominate in the urine of herbivorous animals are derived from the same source namely, from the salts composed of the alkalies with the organic acids contained in the fodder. In precisely the same way is uric acid destroyed or burnt in the organism in presence of free alkali. In the urine of rabbits, to which had been given proportionally large doses of uric acid, in the form of urate of potash (2 to 2J grammes, 30 to 40 grains), no uric acid could be detected. It had been converted into oxalic acid and urea, the amount of which last in the urine exceeded the normal quantity at least five-fold. (Frerichs.) But, as is well known, urea corresponds in composition to carbonic acid. It is carbonic acid, in which half of the oxygen is represented and replaced by its equivalent of amide (N H 2 ). The cause of the so greatly increased combustibility of all these bodies is evidently, as is proved by the most obvious considerations, the alkaline quality of the blood. The herbivora consume in their fodder a quantity of vegetable acids in the free or uncombined state, which, like the portion combined with alkaline bases, are destroyed and disappear in the circulation (the blood being always alkaline, so that these free acids are also converted into alkaline salts). It can hardly be doubted, that in the organism of the herbi- vora, exactly as in that of the carnivora, uric acid must be formed, as an imperfect or intermediate product of the com- bustion of the plastic matters consumed in the change of matter ; but in the normal, healthy state, this uric acid never appears in their urine, rich as it is in free alkali. This fact is satisfactorily explained by the presence of alkaline carbonates in their blood The vegetable acids, when they enter the blood, or the ORGANIC ACIDS IN THE BLOOD. 421 uric acid formed in the body, decompose the alkaline car- bonates in the blood, and form neutral salts, which are destroyed as fast as they are formed by the oxygen present in the blood. The carbonic acid, thus set free, is given oft' by the lungs. The same organic acids which, in the form of salts, that is, accompanied by alkaline bases, disappear so rapidly even in the blood of man, appear in great part unchanged in the urine, when they are taken without these alkalies. Even the most combustible of them, such as tartaric and gallic acids, become, in these circumstances, incombustible in the blood of man. Gallic acid is particularly easy to be recognised in the urine, by its property of striking an inky black with the salts of sesqui-oxide of iron. The cause of this combustibility is the want of the free alkali, which determines and promotes the action of the oxygen. The blood of man (and of the dog, with which a large number of these experiments was made), contains no alkaline carbonate, but only alkaline phosphate. Now, it is certain that the neutral salts of vegetable acids do not alter the alkaline quality of this blood, while the uncombined acids, when they enter the blood, must set free a corresponding amount of phosphoric acid, since they seize a portion of the alkali with which it was combined. This phosphoric acid is not, like the carbonic acid, gaseous and capable of being exhaled by the lungs, but only quits its place in the blood, when compelled by some cause to do so. We must suppose, that that part of the blood which the free vegetable acids reached, totally lost its alkaline character, that it even became transiently acid (a quality which was again removed by the function of the kidneys), and that in consequence of that transient state the vegetable acids, or at least a part of them, lost, in the circulation, their proneness to change and their combustibility. Had the blood, to which free gallic acid was padded, continued alkaline, that acid would have been destroyed ; for the presence of a free alkali and of oxygen is utterly inconsistent with the con- tinued existence of gallic acid. 422 LETTERS ON CHEMISTRY. The peculiarities of the blood of man and of the carnivora, which are determined by the amount of phosphoric acid, appear in. their full significance in the process of secretion. The chemical action of the alkalies meets with a certain resistance from the phosphoric acid combined with them, which resistance does not occur in the blood of the herbivora. The permanent acid reaction of the urine, and the secretion of uric acid, in man and in carnivora, stand in the closest relation to the presence of phosphoric acid in their blood, while the absence of uric acid in the urine of the herbivora is in the same close manner related to the predominant alkaline quality of their blood. The presence of free carbonic acid in the urine of herbivora is in great part determined by the attraction of alkaline car- bonates for carbonic acid. On the other hand, the separation of free acids in the urine of carnivora and graminivora is obviously a condition necessary for the preservation of the alkaline quality of their blood. If we suppose this separation or excretion of free acids to be checked, even transiently, in consequence of a disturbance in the functions of the kidneys, or, in consequence of a mor- bidly accelerated change in the tissues (inflammation, fever), the phosphoric acid of these tissues to be set free and to enter the blood, the alteration in the alkaline quality of the blood must at once exhibit itself by increased excretion of uric acid, and by a change in the respiratory process. These considerations enable us to understand the success, often almost miraculous, which physicians obtain, in many diseases, by a rational diet, by a choice of food made with knowledge of the subject and careful reflection, by mineral waters, and by the vegetable cure or the whey cure. When we replace the bread and the flesh of ordinary diet by juicy vegetables and fruits, the blood is, beyond all doubt, altered in its chemical character ; but this alteration in no way consists in a change of the organic combustible ingre- dient, for the fibrine and albumen of ox-blood do not in the slightest degree differ in their chemical nature from the fibrine and albumen of the blood of animals fed on flesh or grain j URINE OF HERBIVORA. 423 but in a change of the incombustible constituents, in a replace- ment of the phosphoric acid and alkaline phosphates, which exert a disturbing influence in so many diseases (typhoid and inflammatory affections), by alkaline carbonates. There is probably no fact which appears to testify so con- vincingly to the function of the intestinal canal as an organ of secretion, as the absence of iron in the urine generally, and the absence of phosphates in the urine of herbivora. We can readily understand, that no substance can be con- tained in urine which is insoluble in that fluid, and that the phosphates of lime and magnesia are wanting in the urine of the horse and the cow, because a liquid containing so con- siderable a quantity of alkaline and earthy carbonates has no power of dissolving earthy phosphates.* We find in the urine of the horse and the cow no phosphoric acid, although both receive in their fodder, daily, a large amount of phos- phoric acid, in the form of soluble alkaline phosphates, which become constituents of their blood. The chemical analysis of the urine t of the same animals, whose faeces J and whose fodder were also analysed, shows us, that the faeces contain * A solution of carbonate of lime in carbonic acid water, diluted with so much spring water that carbonate of potash or of soda causes no pre- cipitate, gives, on the addition of the smallest quantity of phosphate of soda, immediately, a permanent turbidity from the formation of phosphate of lime. t Urine (after deducting common Salt). J Fasces. Horse. Cow. Horse. Cow. (Arzbacher.) (Arzbacher.) (Buchner.) (Buchner.) Potash . . 28-97 56-74 9-33 17-15 Soda . 1-31 0-61 6-30 Carbonic Acid 27-28 31-04 9 9 Lime . . 27-75 1-74 5-22 7-31 Magnesia * 4-22 4-09 2-03 4-50 Peroxide of Iron 0-79 0-31 2-03 3-34 Sulphuric Acid . 6-48 4-63 3-92 3-23 Silicic Acid . J J j j 59-96 41-00 Phosphoric Acid 7-92 17-05 100-00 10000 100-00 100-00 The horse had daily on an average, 3^ Ibs. of oats, 41bs. of rye bread, lOlbs. of hay, 5 Ibs. of straw. The cow had about 52 Ibs. of dis- tillery dregs from potatoes, 12ibs. of rye straw, 2 Ibs. of hay, 1 lb. of pease straw, lib. of oat straw, lib. of barley straw, 12 Ibs. of beet- 424 LETTERS ON CHEMISTRY. all the phosphoric acid of the food in the form of phosphates of lime and of magnesia (P , 2 M 0) ; and there can be no doubt that the phosphoric acid set free in consequence of the change of matter, which, from the chemical nature of the urine, could not pass out by the kidneys, must be carried from the blood to the intestines, and that hence a part of the intestinal canal performs the same function as the kidneys, as an organ of excretion. It is difficult, either from the anatomical or chemical point of view, to form a clear notion of this process of excretion, of the existence of which we perceive the most convincing evidence in diseased states (in diarrhoea, for example). But in the study of nature the diffi- culty of explanation does not destroy the truth of a fact. Besides the incombustible constituents above mentioned, the blood of man and animals contains a certain amount of common salt and of iron. The quantity of common salt usually amounts to upwards of one-half of the total weight of all the incombustible substances in the blood. The difference of food has no perceptible influence on the amount of common salt in the blood. The blood of a dog, fed for eighteen days on flesh, contained the same proportion of common salt as after twenty days feeding with bread. The common salt in the blood of man, of the sheep, pig, ox, and calf amounts to from 50 to 60 per cent, of the total weight of the ash. The difference in the quantities of salt obtained in different analyses depends in part on the difficulty root. Of this mixed fodder, Mr. Porter analysed the ashes of the potato dregs, the oats, and the hay. Potato Dregs Soluble Constituents ie Ash of Dregs. 54-18 6-17 11-99 5-91 8-72 12-12 100-00 100-00 100-00 100-00 Hay. Oats, from Distillery. Potash 20-08 12-94 38-52 Soda 10-84 2-02 4-47 Phosphoric Acid 17-35 15-43 16-78 Lime . 8-24 3-00 5-19 Magnesia 4-00 7--08 7-33 Peroxide of Iron 1-82 0-60 1-50 Common Salt . 5-09 4-00 Sulphuric Acid 2-10 0-49 6-10 Silicic Acid . 30-00 53-97 2-84 Carbonic Acid 0-67 12-27 COMMON SALT IN THE BLOOD. 425 of avoiding the volatilisation of common salt in the incine- ration of blood ; and the unequal per centage of salt in the blood of different animals depends partly on the varying amount of other constituents, such as phosphoric and carbonic acids. The great proportion of common salt in the blood is suffi- ciently remarkable, to be considered with reference to the question of its necessity, as a condition of the vital process. It is unnecessary particularly to point out, that all the common salt in the blood is derived from the food ; but if we compare the ashes of the vegetable food of the cow and horse with the ashes of their blood, we perceive a very strik- ing difference. The amount of that salt in the ashes of the blood is much greater, often ten-fold greater than in the ashes of the fodder. A comparison of the ingredients of the ashes of the urine with those of the ashes of the blood shows, moreover, that the amount of common salt in the ashes of the urine is always less than in those of the blood, and cor- responds with that in the ashes of the food. These facts seem to point to the conclusion, that in the circulating system some cause is in operation, which (as the proportion of salt in the blood never goes beyond a certain limit), opposes the increase as well as the diminution of its quantity ; that, con- sequently, the common salt is not merely an accidental, but an essential and constant ingredient of the blood, and that its quantity is fixed within certain limits. Of the various kinds of vegetable food, seeds contain the smallest amount of common salt ; green vegetables and meadow grass (especially Lolium perenne) among the plants of the Continent, contain the largest proportion. It is not easy to determine the full significance and value of salt for the vital process, with the same certainty as we can in the case of phosphoric acid and lime, the indispen- sability of which for the formative process is an established fact, since they form parts of all the tissues. Salt serves in the organism to assist and promote the general changes, without taking a share, by its elements, in the formative process. No organised part or tissue contains chlorine in 426 LETTERS ON CHEMISTRY, chemical combination ; but there is no fluid of the animal body in which chlorine is absent as a constituent. In animals, which, like those of the Continent, receive in their food only salts of potash, and, except chloride of sodium, no compound of sodium or of chlorine, we discover the elements of the salt, but separated, and in different parts. In the whole muscular system, in the juice of flesh, an abundant quantity of chlorine is found, but combined with potassium, not with sodium ; this chlorine is derived from the common salt. In the secretion of the liver, the bile of land animals, we find a predominating quantity of oxide of sodium, the sodium of which was received in the food as common salt. In the blood of the horse, the cow, and herbivora in general, the quantity of carbonate of soda exceeds that of carbonate of potash two- or three-fold, although the ashes of their food hardly contain a trace of carbonate of soda. These relations, from their permanence and fixity, are very trustworthy indications that sodium and soda, from their peculiar properties, are especially adapted for the changes occurring in the blood and blood- vessels, and that potassium or potash, for the same reason, is peculiarly fitted for the changes going on in the muscular sys- tem ; and that these two alkalies, although so much alike in many other properties, cannot mutually replace each other with reference to all the purposes which they serve. In the blood of man, and of animals fed on grain, the phosphate of potash is always accompanied by common salt ; but we know that these two salts cannot exist together without mutually decom- posing each other, yielding phosphate of soda, which in its properties approaches most closely to the carbonate of soda, and chloride of potassium.* Moreover, when we consider that the efficient free acid often occurring in digestion is hydrochloric acid,t which is derived from common salt, all these facts, taken together, * When a moderately strong solution of phosphate of potash is mixed with one of common salt, and left to stand in the cold, phosphate of soda soon crystallises out in fine crystals. t The early observations of Prout and L. Ghnelin have lately been confirmed, for many cases, by Dr. Schmidt, of Dorpat. NECESSITY OF SALT FOR THE VITAL PROCESS. 427 seem entitled to be regarded as irrefragable proofs of the necessity of the presence of salt for the vital process, and of the addition of salt to the food of men and the fodder of animals. The action of free hydrochloric acid on the plastic consti- tuents of food, is very remarkable. The gluten of grain and the fibrine of flesh, for example, dissolve in water which has been hardly acidulated with hydrochloric acid, readily and rapidly at the temperature of the body ; and this solubility does not increase, but diminishes, when the proportion of acid in the liquid is increased ; so that all the dissolved matter can be again precipitated by moderately strong hydro- chloric acid. A solution of common salt has the same effect as the strong acid. The same water, which, by the addition of y-oViy f hydrochloric acid, becomes a powerful solvent for the plastic substances, loses its solvent power on the addition of rather more than 3 per cent, of common salt ; and all the gluten or fibrine may be precipitated from the acid solution by a solution of salt. The relations now pointed out between the elements of common salt and the organic processes, are certainly not the only ones which belong to this compound, so remarkable on account of its universal diffusion in nature, and its presence in all organised beings. It is more than probable that it promotes, nay even determines, certain changes and opera- tions, by virtue of its peculiar properties as a salt. We need only recall the fact, that common salt possesses the property, quite unusual among salts, of forming with urea a chemical compound which crystallises in beautiful large, clear, rhombic prisms, and which is always found in urine containing common salt.* Even in the vitreous humour of the eye, the urea is accompanied by common salt. By * Among the salts, only some nitrates form similar compounds with urea. The presence of the compound of urea with common salt in the urine of man and animals, is the reason why we often obtain no nitrate of urea from urine, moderately concentrated, and why in that which is more concentrated, there is left, after the addition of nitric acid, more urea in solution than corresponds to the solubility of the nitrate. 428 LETTERS ON CHEMISTRY. combining with common salt, urea loses certain properties which belong to it as an organic compound ; and accurate observations may perhaps show, that the absence of urea, the ultimate product of the organic change of matter, as well as of common salt, in the muscular system, and the passage of urea into the circulation, and its excretion by the kidneys, have a closer relation with the presence of common salt than is generally supposed. If, further, we consider, that instinct leads us to add salt to amylaceous food in much larger proportion than to other food ; that potatoes, to most men, are hardly eatable without salt ; we are involuntarily reminded of the remarkable com- pound which common salt forms with grape-sugar, the pro- duct of the digestion of starch. It is known that diabetic urine generally contains this compound ; and the presence of common salt cannot be without some influence on the excre- tion of sugar by the kidneys. I cannot here omit to mention, that agriculturists have endeavoured to solve the question as to the necessity or the profit of adding salt to the fodder of live stock, in their own way. The result of the excellent experiments of Boussin- gault is, in this respect, decisive, clear, and intelligible. The addition of salt to the fodder had no influence on the quan- tity of flesh, fat, or milk obtained from the animals ; " but," says Boussingault, " the salt appeared to have a favourable effect on the appearance and quality of the stock. After the first fourteen days, we observed no perceptible difference between the two lots (each of three oxen) ; but in the course of the month following, the difference was visible even to the unpractised eye. In the beasts of both lots, the skin to the feel was fine and sound ; but the hair in the oxen which had got salt, was smooth and shining, that of the others was dull and erect. On prolonging this experiment, these signs became still more prominent. In the animals of the second lot, after they had had no salt for a year, the hair was matted, and the skin here and there devoid of hair. Those of the first lot, on the contrary, retained the look of stall-kept beasts ; their liveliness and frequent indications of a desire EFFECTS OF SALT IN FOOD. 429 to leap, contrasted strikingly with the heavy gait and cold temperament observed in those of the second lot. There is no doubt," continues Boussingault, " that a higher price would have been obtained in the market for the oxen reared under the influence of salt." These experiments are most instructive. In the oxen which only had as much salt as was contained in their fodder, the quantity of salt was insufficient for the secretory process. There was wanting the means of transport for a number of substances which, out of the body, excite disgust ; their whole frame, the blood, flesh, and all the juices were loaded with these ; for the external surface of the skin is a mirror of the state of the interior. The other oxen, which daily had salt added to their fodder, remained healthy, even in the mode of life to which they were confined, which corresponded but little to their nature, and with excess of food and deficient exercise. Their blood remained pure, and well fitted for all the purposes of nutrition. In the salt they had a powerful means of resistance to external causes of disturb- ance to health, which, in the actual circumstances, was indispensable to them. The body of the others was, in regard to disease, like a fire-place, heaped with the most inflammable fuel, which only requires a spark in order to burst into flame and to be consumed. Salt does not act as a producer of flesh ; but it neutralises the injurious action of the conditions, which must be united in the unnatural state of animals fed or fattened in order to produce flesh ; and the advantages attending its use can hardly be estimated too highly. Many agriculturists, however, have drawn very different conclusions from these experiments. As the addition of salt yields to them (the farmers) no profit, since, by the outlay on salt, nothing is gained in flesh, they concluded that salt is of no use whatever ; nay, these experiments have actually been abused, as proofs and arguments against the reduction of the impost on salt, of all taxes on the Conti- nent that which is the most odious, the most unnatural, and the most disgraceful to human reason. We may here see 430 LETTERS ON CHEMISTRY. that more wisdom is displayed in the instinct of an ox or of a sheep, than in the arrangements of the being who, strange to tell, often regards himself as the image of Him who is the perfection of all kindness and of all reason. Besides its chemical characters, common salt possesses a physical property, which gives it a special importance in the vital processes ; because those other salts which partake this property with it, are not consumed either by men or animals in their ordinary mode of life. This most interesting property may easily be rendered visible with the aid of a very simple apparatus. If, for example, over one opening of a glass-tube, four to six inches long, and about a quarter of an inch wide, we tie a moist membrane (intestine or bladder, &c.), and fill it to one-half with spring water, and then place it in a glass of the same water, so that the water within and without the tube stands at the same level, we observe, even after hours or days, no change in the level of the two liquids. But if we now add, to the water in the tube closed with bladder, a few grains of common salt, we shall see, after a few minutes, the water in the tube rise above the level of that in the glass ; it moves upwards. If we add salt also to the water in the glass, and in such quantity that the proportion of salt in the two liquids is the same, no change of level occurs. But if more salt, in propor- tion, be added to the water in the glass than to that in the tube, the opposite change takes place : the water in the tube sinks ; that in the glass rises. We see from this, that the spring water flows towards the saline water, and the weaker solution of salt towards the stronger; as if forced by an external pressure to pass through the pores of the membrane, in opposition to the law of gravitation. By the mere addition of common salt to the water, the tube with the bladder acquires the property of a pump, and sucks up water with a force which, in many cases, is equal to the presence of a column of mercury, two or three inches in height. ENDOSMOSIS OF SOLUTION OF SALT. 431 When the tube, closed by a very thin membrane, is half- filled with ox-blood deprived of its fibrine, and placed in a glass of warm water (at about 100 F.), the blood, after a few minutes, rises, just as the solution of salt did. The water flows towards the blood. That the presence of salts in the liquor sanguinis has a great share in this suction, we perceive in this, that the liquid which may easily be obtained by pressure from blood coagulated by heat, and which contains common salt and other salts, when introduced into the tube instead of the blood, exhibits precisely the same phenomena. The power of the membrane, to cause water to flow towards that side of it on which the salt is found, depends, therefore, on the salt. When the liquids on both sides, contain equal proportions of salt, no flow takes place either way. The liquid invariably flows towards that side where most salt is present, and it flows the more rapidly, the greater the difference in the proportion or per centage of salt between the two liquids. When we add to the solution of salt a free alkali (in the form of carbonate or phosphate), the power of suction is very perceptibly increased ; and when the liquid in the outer glass is slightly add, and the solution of salt in the tube is alkaline, the flow (of the acid to the alkaline liquid) takes place with the greatest velocity. Any one who takes the trouble to repeat these attractive experiments will obtain, by the mere contemplation of them, a perfect insight into the essence of the organic process of suction. In the animal body, indeed, are united all the conditions for rendering the circulating system, by means of the blood, a most perfect suction pump, which performs its duties without stopcocks or valves, without mechanical pressure, nay, without regular canals or passages for the transmission of the fluids. The solution formed in the digestion of food in the stomach is acid, the blood is a saline and alkaline fluid. The whole digestive or intestinal canal is surrounded by a system of infinitely ramified blood-vessels, in which the 432 LETTERS ON CHEMISTRY. blood moves with great velocity. By means of the urinary apparatus, the water which has flowed into the blood is immediately filtered off, and the circulating fluid is thus always kept in the same state of concentration. We can now easily understand the effects produced on the organism by waters containing different proportions of salt. If, for example, we drink, fasting, every ten minutes a glass of spring-water, the proportion of salt in which is far below that of the blood, there is passed after drinking only the second glass (each glass being supposed to contain four ounces) a quantity of coloured urine, very nearly equal in bulk to the first glass of water. t When in this way twenty glasses have been taken, there have been nine- teen evacuations of urine, the last of which is nearly colourless, and in the proportion of salt but slightly exceeds spring water. If we make the same experiment with spring water to which has been added some salt, about as much as the blood contains (from 075 to 1*0 per cent.) no unusual evacuation of urine occurs. It is hardly possible to drink more than three glasses of such water ; a sensation of repletion, pressure, and weight at stomach indicate that water, having a per centage of salt equal to that of the blood, requires a far longer time for its absortion into the circulation. Lastly, if we take a solution of salt, the per centage of salt in which is somewhat higher than in the blood, there occurs the opposite of absorption, namely, purging. We see that the absorptive power of the blood-vessels for water varies according to the proportion of salt in the water. If that be less than in the blood, it is absorbed with great rapidity ; when the proportion of salt in both fluids is the same, an equilibrium occurs ; if the water contain more salt than the blood, this salt-water is expelled, not like the weaker solution, through the kidneys, but through the intestinal canal.* * " Common salt has generally become a very great necessity, even for the rudest nations. In not a few countries it is one of the most valuable VEGETABLE AND ANIMAL FOOD. 433 LETTER XXXII. Vegetable and Animal Food Composition of Flesh ; its Fibrine, Albumen, &c. Proper mode of boiling and roasting Meat, and of making Soup Constituents of watery Extract of Flesh ; Kreatine, Kreatinine, &c. Value of S >up and of Flesh as food Importance of true Extract of Flesh for Hospitals, Armies, &c. Portable Soup of Commerce was chiefly Gelatine, which has no Nutritive value Directions for making pure Extract of Meat Its great value depends on its Inorganic Salts The loss of Nutritive value in Salted Meat depends on the Expulsion of a great part of the juice Different kinds of Meat differ in Nutritive value Veal inferior to Beef, and why Importance of Iron Cheese, Fish, Salted Fish, Eggs, are all deficient in Alkalies and Iron This is probably the reason why they are admitted in fasting Table of the relative proportion of Nitrogen and Carbon in Animal Substances, from Albumen to Urea Chemical relations of Albumen, Fibrine, Caseine, Gelatine, Chondine, Bile, and Urine Table of the formulae deduced from analyses alone Illustrations of their derivation one from the other Grinding of Grain Flour and Bran Brown Bread of the entire flour preferable to White Bread from bolted flour Piye Bread Adultera- tions of Bread ; Blue Vitriol ; Alum, Lime-water should be used instead Baking Yeast preferable to Carbonate of Soda and Muriatic Acid Substitutes for Bread in times of scarcity are either merely local or else fallacious. The only true gain would be to save what is thrown away on the Bran, and the Gluten wasted in starch-manufactories Superior digestibility of Bread from the entire Meal, or the Pumpernickel of Westphalia The Culinary Art is empirically far advanced Food for different ages Effects of Vegetable and Animal Diet Value of Wine The abuse of Spirits not so much the cause as the effect of poverty Total abstainers eat very much more than wine-drinkers Uses of Tea, Coffee, Chocolate, &c. Theine, or Caffeine, compared to Kreatine and Sugar of Gelatine Mineral elements of Tea, &c. Price of Meat in years of scarcity ; and of Bread Men living on Meat must eat a great deal, and take violent exercise Importance of Agriculture compared with Hunting by an Indian Chief Science teaches the economy of force Tendency of riches to inequality of distribution, and thence to universal circulation Money, in the organism of the State, compared to the blood corpuscles in the body, by the circulation of which the change of matter is effected, and life kept up All human actions, as is proved by the statis- tics of births, deaths, crimes, and justice, are under strict natural laws True science ascertains these laws, and teaches men to observe them. BREAD and flesh, or vegetable and animal food, act in the same way with reference to those functions which are mercantile commodities. In several countries of Africa men are sold for salt ; among the Gallas and on the coast of Sierra Leone, the brother sells F F 434 LETTEKS ON CHEMISTRY. common to man and animals j they form, in the living body, the same products. Bread contains, in its composition, in the form of vegetable albumen and vegetable fibrine, two of the chief constituents of flesh, and, in its incombustible constituents, the salts which are indispensable for sanguification, of the same quality and in the same proportion as flesh. But flesh contains besides these, a number of substances which are entirely wanting in vegetable food ; and on these peculiar constitu- ents of flesh depend certain effects, by which it is essentially distinguished from other articles of food. When finely chopped muscular flesh is lixiviated with cold his sister, the husband his wife, parents their children, for salt ; in the district of Accra (gold coast) a handful of salt, the most valuable mer- chandise after gold, will purchase one or even two slaves." " Only very few nations refrain from the use of salt entirely" (? the author gives no instance of such entire abstinence), ' ' or try to supply its place by surrogates" (pp. 1 and 2). "In the northern parts of the hill countries of tropical Africa, salt, in consequence of the long carriage through the desert, becomes so dear, that only the rich can procure it. ' Even Mungo Park mentions that among the Mandingoes and other negro tribes in the interior, the expression "he flavours his food with salt," is synonymous with that of, he is a rich man. Park experienced, from the necessity of giving up the use of salt, especially when long confined to vegetable food, a longing after salt, such as he was unable to express in words. Gallic also assures us that 'the natives of Rankan are seldom able to use salt with their food on account of its high price, and that it is there an article of luxury.' The Mandingoes and Bambaras use salt only on certain festival days." (Lehrbuch der Salinenkunde, Karsten, Berlin, 1846, pp. 720, 724, 754, 755.) " There are countries where salt must be given to animals to keep them alive. According to Warden, for example, in the northern districts of Brazil, domestic animals died when they did not receive a fixed portion of salt or saline sand ; and according to Roulin, when the cattle did not find salt in the plants, in the water, or in the earth, the females became less prolific, and the herd rapidly diminished in number." (Moglin'sche Annalen, II., 1847, p. 29.) In a prize essay on the use of salt, crowned by the Academy of Medi- cine in Brussels, Dr. De Saive remarks, that ' ' Salt increases the fertility of the male, and the tendency of the female to conceive, and doubles the power of nourishing the foetus. During the period of suckling, the salt given to the mother renders the sucking animal stronger, and the milk more abundant and more nutritious. Salt accelerates growth, and renders the wool of sheep finer. The flesh of animals which have had abundance of salt is better flavoured, more nutritious, and more easily digested, than that of animals which receive no salt in their food." (Journal de Chiinie Medicate, 1849, p. 127.) SOLUBLE EXTKACT OF FLESH. 435 water, and pressed out, there is left a white fibrous residue, consisting of the true muscular fibres, cellular tissue, vessels, and nerves. When the lixiviation is complete, the water dissolves from 16 to 24 per cent, of the weight of the dry flesh. The fibrine of flesh, the chief constituent of the muscular fibre, constitutes three-fourths of the weight of the lixiviated residue. If this residue be heated to between 158 and 177 F., the fibres contract together, shrink, and become horny and hard ; a change, a kind of coagulation takes place, in consequence of which the fibres of flesh lose the power of sucking up water like a sponge, and retaining it. Water flows out, for, without the addition of water the pressed residue, when heated, soon swims in water. The lixiviated flesh, when boiled, with water, is, like the water in which it has been boiled, tasteless, or has a slight nauseating taste ; it cannot be masticated, and even dogs reject it. All the savoury constituents of flesh are contained in the juice, and may be entirely removed by lixiviation with cold water. When the watery infusion of flesh thus obtained, which is commonly tinged red by some of the colouring matter of blood, is gradually heated to boiling, the albumen of flesh separates, when the temperature has risen to 133 Fahr., in nearly colourless cheesy flocculi ; the colouring matter of the blood is not coagulated till the temperature rises to 158. The liquid is now pale yellowish, clear, and it reddens litmus paper, proving the presence of a free acid. The proportion of the albumen of flesh separated as a coagulum by heat is very various, according to the age of the animal. The flesh of old animals often yields no more than 1 to 2 per cent. ; that of young animals as much as 14 per cent. The infusion or extract of flesh, after being freed by boiling from albumen and the colouring matter of blood, has the aromatic taste, and all the properties of the soup made by boiling the flesh. When evaporated, even at a gentle heat, it becomes darker coloured, finally brown, and acquires the F F 2 436 LETTERS ON CHEMISTRY. flavour of roast meat. When dried up, there is obtained a brown, somewhat soft mass, amounting to 12 or 13 per cent. of the weight of the original flesh (supposed to be dried). This extract is easily soluble in cold water, and when dis- solved in about thirty- two parts of hot water, with the addition of some salt, gives to this water the taste and all the peculiar properties of an excellent soup. The intensity of the flavour of the dry extract of flesh is very great ; none of the means employed in the kitchen is comparable to it in point of flavouring power. The residue of flesh after exhaustion with cold water, is of the same quality in different animals so that it is im- possible in this state to distinguish beef from poultry, venison, pork, The formula of Gelatine / -j- 10 eqs. of Oxygen f The formula of Albumen 4-10 eqs. of Water + 56 eqs. of Oxygen ^contains the ele- ments of 2 Gelatine, and 1 Choleic Acid. 1 Albumen of Blood. 1 Gelatine. 1 Cholic Acid. 2 Uric Acid. 8 Water. 1 Cholic Acid. 3 Uric Acid. 12 Water. 1 Choleic Acid. 2 Cholic Acid. 12 Urea. 36 Carbonic Acid. We regard it as a truth, which requires no special proof, that from albumen are derived gelatine and choleic acid as well as the fibrine of blood ; and that, from gelatine and chondrine, uric acid and urea are derived. The above for- mulae express, according to the actual state of our knowledge, the proportions in which this may occur, not those in which RELATIONS OF ALBUMEN, FIBRINE, CASEINE, &c. 457 it actually does occur. Herein consists the hypothetical parts of these formulae ; in this, namely, that we have no evidence of the actual occurrence of these transformations and resolutions of one body into others in the proportions here given. These have only probabilities in their favour. But it appears with certainty from these formulae, that albumen, with the addition of 10 eqs. of water, contains pre- cisely the elements of the substance of membranes and of choleic acid ; that the fibrine of blood is perhaps albumen half-converted into gelatine ; that gelatine, under the influ- ence of the respiratory process, may be resolved exactly into cholic acid, uric acid or urea, carbonic acid and water ; that when uric acid is formed from gelatine in the change of matter, the elements of cholic acid remain ; and that the production of the constituents of urine must be very closely related to that of the constituents of the bile. From these formulae we may further conclude, that the nutritive value of the caseine of milk is greater for the child, and less for the adult than that of albumen ; for it is cer- tain that nature requires, and applies to certain purposes in the body of the young animal, the excess of the elements which caseine contains beyond those of albumen ; and that these objects have no longer any importance on the adult animal. We may also conclude, from them, that the gelati- nous substances taken in the food are not adapted to san- guification, while they increase the production of the con- stituents of the bile and of the urine, as has long been recognised by experience in regard to the latter.* The gluten of grain, and the albumen of vegetable juices, are identical in composition with the albumen of blood. * It is known that, by the action of oxidising agents on cholesteriue, a peculiar acid, cholesteric acid, is obtained (Redtenbacher) ; and that the same acid may be obtained in the same way from cholic and choleic acids, and from no other constituent or product found in the animal body. (Schlieper.) This establishes a connexion between the acids of the bile and the peculiar fat which often occurs in such enormous quantity in that secretion. It is not impossible that cholesterine may be a product of the destruction of the acids of the bile in the vital process. Hitherto, no one knows what becomes of these acids. 458 LETTERS ON CHEMISTRY. Vegetable caseine has also the composition of animal caseine. The different kinds of grain are not alike in the amount of incombustible constituents or inorganic salts they contain. In wheat, the phosphoric acid varies from 40 to 48 (Th. Way and Ogston), even to 60 per cent. (Erdmann.)* There are varieties of wheat, the ashes of which are, in quantity and in the relative proportion of the salts, the same as those of boiled and lixiviated meat ; and it cannot be maintained that bread, made of such flour, would, if the only food taken, support life permanently, t The finest wheat-flour contains more starch than the coarser; the bran of wheat is proportionally richer in gluten. Fine American flour is one of the varieties which is richest in gluten, and is, consequently, one of the most nutritious. Rye and rye-bread contain a substance resembling starch- gum (or dextrine, as it is called) in its properties, which is very easily converted into sugar. The starch of barley approaches in many properties to cellulose, and is, therefore, less digestible. Oats are particularly rich in plastic sub- stances ; Scotch oats richer than what is grown in England or in Germany. This kind of grain contains, in its ashes, after deduction of the silica of the husks, very nearly the same ingredients as are found in the ashes of the juice of flesh. In order to promote the separation of the flour from the * Ashes of wheat, analysed by Erdmann, after deducting peroxide of iron (1-33 per cent.), silica and sand (3'37 per cent.): Alkaline Phosphates (P 5 , 2 M 0) . . . . 49-18 Earthy Phosphates (P 5 , 2 M 0) 23 '13 Free phosphoric acid 27 '69 100-00 Compare with this the excellent analysis of Th. Way and Ogston. t "Is the finest flour as perfect a food as the entire meal ? I think not, and I beg here to recall the experiment of Magendie, in which a dog, exclusively fed with white wheaten bread, died after forty days ; while another dog, fed on black bread (brown bread, made of the flour with the bran) lived on without any disturbance of his health." (Millon, Comptes Rendus, xxviii. p. 40.) ADULTERATIONS OF BREAD. 459 husks, the corn is, by many millers, slightly moistened before grinding. If this moisture be not thoroughly removed from the flour by very careful drying by artificial heat, it causes the flour, when kept, to spoil ; it acquires a musty flavour, cakes together in lumps, and feels harsh like gypsum. The dough made of this flour becomes greasy, and yields a heavy dense bread, not porous as it ought to be. This spoiling depends on an action of the gluten on the starch, which action is promoted by the moisture, and by which acetic and lactic acids are formed in the flour. These acids render the gluten soluble in water, which, naturally, it is not. Many salts render the gluten again insoluble, apparently, by forming with it a chemical combination ; and the bakers of Belgium discovered, about twenty years ago, how to bake from damaged flour, by adding sulphate of copper (a poison) to the dough, a bread in appearance and external properties as beautiful as from the best flour. This mode of improving its physical properties, of course, deteriorates its chemical properties. Alum has the same effect as sulphate of copper. When added to the dough, it renders the bread very white, elastic, firm, and dry ; and the London bakers, in conse- quence of the demand for bread whiter than the English and American flour, usually so good, yields, appear to have been compelled to add alum to all flour in the baking. I saw in an alum manufactory, in Scotland, little mounds of finely ground alum, which was destined for the use of the London bakers. Since phosphoric acid forms with alumina a compound hardly decomposable by alkalies or acids, this may perhaps explain the indigestibility of the London bakers' bread, which strikes all foreigners. A small quantity of lime- water, added to the musty or damaged flour, has the same effect as the alum or sulphate of copper, without being fol- lowed by the same disadvantages. The careful mixture with the saliva during the mastica- tion of bread, is a condition essential to the rapid digestion of the starch. Hence the increase of digestibility obtained in bread by the porous form given to it. 460 LETTERS ON CHEMISTRY. This porosity and lightness are produced in the dough by a process of fermentation. Beer-yeast is added to the dough, which brings into fermentation the sugar formed by the action of the gluten on the starch ; and the open porous texture of the mass is the result of the carbonic acid thus formed in every part of it. In making rye-bread, sour dough is employed ; there is added to the fresh dough of rye-meal, a portion of old dough- in a state of fermentation, from a former baking, and by its action on the sugar there is always formed a certain amount of acetic and lactic acids, in consequence of which the bread has a slightly acid reaction. Many chemists are of opinion that the flour, by the fermentation in the dough, loses somewhat of its nutritious constituents, from a decomposition of the gluten ; and it has been proposed to render the dough porous without fermen- tation, by means of substances which, when brought into contact, yield carbonic acid. But on a closer investigation of the process, this view appears to have little foundation. When flour is made into dough with water, and allowed to stand in a gentle warmth, a change takes place in the gluten of the dough, similar to that which occurs after the steeping of barley, in the commencement of germination in the seeds, in the preparation of malt ; and in consequence of this change, the starch (the greater part of it in malting, in dough only a small per centage) is converted into sugar. A small portion of the gluten passes into the soluble state, in which it acquires the properties of albumen, but by this change it loses nothing whatever of its digestibility or of its nutritive value. We cannot bring flour and water together without the formation of sugar from the starch, and it is this sugar, and not the gluten, of which a part enters into fermentation, and is resolved into alcohol and carbonic acid. We know, that malt is not inferior in nutritive power to the barley from which it is derived, although the gluten contained in it has undergone a much more profound altera- tion than that of flour in the dough, and experience has BEST PROCESS FOR MAKING BREAD. 461 taught us, that in distilleries where spirits are made from potatoes, the plastic constituents both of the potatoes and of the malt which is added, after having gone through the entire course of the processes of the formation and the fer- mentation of the sugar, have lost little or nothing of their nutritive value. It is certain, therefore, that in the making of bread there is no loss of gluten. Only a small part of the starch of the flour is consumed in the production of sugar, and the fermentative process is not only the simplest and best, but also the cheapest of all the methods which have been recommended for rendering bread porous. Besides, chemical preparations ought never, as a general rule, to be recommended by chemists for culinary purposes ; since they hardly ever are found pure in ordinary commerce. For example, the commercial crude muriatic acid, which it is recommended to add to the dough along with bicarbonate of soda, is always most impure, and very often contains arsenic, so that the chemist never uses it, without a tedious process of purification for his purposes, which are of far less importance. The plans which have hitherto been proposed, with the view of replacing the flour in making bread, so as to render it cheaper in times of scarcity and famine, only prove how far we are still removed from a rational system of dietetics, founded on scientific principles. The price of food depends on the same causes, and is regulated by the same laws as that of fuel. If we take the trouble to compare the prices of the various kinds of coal, or of firewood, or of browncoal (woodcoal), and turf or peat together, we shall find that the number of pence paid for a given weight or measure of these forms of fuel, is, as nearly as possible, in direct propor- tion to their true value, that is, to the number of degrees of heat which they give out in burning. In a district where beech, oak, and fir-wood are burned, it is a matter of indifference, in regard to price and heating power, which wood is chosen. Here the preference is given according to the object in view. For large, wide, or long fire-places fir-wood is the best, because its flame extends farthest ; for 462 LETTERS ON CHEMISTRY. small narrow fire-places beech- wood is preferred on account of the charcoal it yields. In estimating such values, one person may err, but the daily experience of many thousands neutralises the mistakes of individuals. The average price of the various kinds of food in a large country is, as a general rule, the measure of their nutritive value ; the variations in price in different places arise from local causes (ease or difficulty of transport, good or bad roads, rivers, canals, &c.). For the purposes of nutrition rye is not cheaper than wheat ; rice and potatoes are not cheaper than grain. Wheat flour cannot be replaced advantageously, as far as this quality is concerned, by any other kind of flour. It is only in times of scarcity or famine, that these relations of value are somewhat modified. Potatoes and rice then reach a higher price than usual, because in addition to their true nutritive value, they possess another, namely, their value as respiratory matter, which in times of plenty is not reckoned. To make bread cheaper, it has been proposed to add to dough potato starch or dextrine, rice, the pressed pulp of turnips, pressed raw potatoes, or boiled potatoes ; but all these additions only diminish the nutritive value of bread. Potato starch, dextrine (starch-gum), or the pressed pulp of turnips and beet-root, when added to flour, yield a mixture, the nutritive value of which is equal to that of the entire potato or lower still ; but no one can consider the change of grain or flour into a food of equal value with potatoes or rice as an improvement. The true problem is to render potatoes or rice similar or equal to wheat in their effects, and not vice versd. It is better, under all circumstances, to boil the potatoes and eat them as such, than to add potatoes or potato starch to flour before it is made into bread ] which should be strictly prohibited by police regulations, on account of the cheating to which it would inevitably give rise. The addition of peas or bean meal, or of skim-milk cheese to rye flour, as is done in Bavaria (Dr. Vogel), answers the purpose much better, but nothing is thereby gained in price. NUTRITIVE VALUE OF GLUTEN OF WHEAT. 463 The only real saving and profit in this way is that made by using such articles of refuse as are not employed for food in the ordinary course of events. In England, for example, many thousand cwts. of the finest and best flour are used to yield starch for dressing cotton goods, and the gluten, which forms the refuse of this manufacture, amounting to from 12 to 20 per cent, of the dried flour, is, for the most part, lost as food for men. In the experiments of the French academicians dogs were fed for ninety days exclusively with the gluten of flour, which was devoured raw by the animals without any repugnance, and without interruption. No perceptible disturbance of their health occurred.* With the exception of the organic substances in the juice of flesh, there is no substance which approaches more nearly to the fibrine of flesh, in its properties and nutritive value, than the gluten of wheat. When boiled with a little salt and water, dried, and ground to a coarse meal, gluten is easily preserved, and with the addition of some extract of meat and kitchen vegetables, it yields the strongest, best- flavoured, and most nutritious soup. As a provision for ships and fortresses the dried gluten of wheat (along with extract of meat) would enable us to save a large quantity of meat. In the brewing of beer, as is well known, a separation takes place between the sanguigenous matters of the barley and the starch. Of the former, those portions which dissolve in the wort, and are separated as yeast during the fermenta- tion, are lost for the purpose of nutrition. Only that portion which remains undissolved with the husks is used as fodder for cattle, and much prized, especially for milch cows. In making the infusion, or worts, there is deposited above the husks a dough-like mass, consisting of the finest suspended * Gluten, from a starch manufactory, yielded 1 to 1| per cent, of ashes, which contained 7'87 per cent, of potash, 2*14 of soda, 17 '31 of lime, 12 '08 magnesia, 7' 13 peroxide of iron, together 4 7 "13 of bases, with 52'08 of phosphoric acid, 0'69 of sulphuric acid, and 0'09 of chlorine. (Kekute.) 464 LETTERS ON CHEMISTRY. particles of the ground malt, and which is well known to German brewers under the name of Oberteig (upper dough). This upper dough contains as much as 26 per cent, of plastic matter, and from 4 to 8 per cent, of starch, and, when added to an equal weight of flour, the large amount of water contained in it being taken into account, yields an unexcep- tionable bread. The breweries of Wiirtemburg yield annually 30,000 cwt. of this malt dough, which might furnish 17,000 cwt. of bread. (Schlossberger.) All these means of relieving the necessities of the poor in years of famine are only local, and amount to little in comparison with the consumption, for the inhabitants of a large country. There is only one permanent means of saving for the largest population, which is, that the wheat or rye, ground fine, should be used for baking bread, unbolted, that is, the flour along with the bran, and the whole of the nutriment existing in the grain thus rendered available for man. In 1658, an ordinance of Louis XIV. prohibited, under heavy pecuniary penalties, the grinding of the bran a second time ; which according to the then existing arrange- ments of flour-mills, must have caused a loss of 40 per cent. In the seventeenth century, Vauban estimated the annual consumption of a man at nearly 712 Ib. of wheat, a quantity which now suffices nearly for two men ; and by the improvements in mills there are now gained to the population immense masses of nutritious matter, of the annual value of many millions, which were formerly used for animals alone : whereas for the feeding of animals the bran may be far more easily replaced by other food, not in the least adapted for the use of man. The very high value of bran as food has been long ago pointed out, especially by Millon. Wheat does not- contain above 2 per cent, of indigestible woody fibre, and a perfect mill, in the most extended sense, should not yield more than that proportion of bran ; but, practically, the best mills always yield, even now, from 12 to 20 percent. (10 per cent, coarse bran, 7 fine bran, 3 bran flour) ; and the ordinary mills produce as NUTRITIVE QUALITY OF BRAN. 465 much as 25 per cent, of bran, containing 60 or 70 per cent. of the most nutritious constituents of the flour. It is evident, that by baking bread with unbolted flour the mass of bread may be increased from one-sixth to one- fifth, and the price of it lowered by the difference between the price of the bran as fodder for cattle and that of the flour gained by not bolting the flour.* As an addition to the flour, in times of scarcity, the bran has even a much higher value, and cannot be replaced by any other nutri- tious matter. The separation of the bran from the flour by bolting is a matter of luxury, and injurious rather than beneficial as re- gards the nutritive power of the bread. In ancient times, down to the period of the Emperors, no bolted flour was known. In many parts of Germany, especially in Westphalia, the entire meal, including the bran, is baked into the brown bread called Pumpernickel ; and there is no country where the digestive organs of the population are in a better condition. The boundaries between the Lower Rhine and Westphalia may be traced by the very remarkable size of the remains of preceding meals left by passengers behind the hedges : and possibly it is from observing these excellent evidences of the digestive capacity of the Westphalians that English physi- cians have been induced to recommend to the great in Eng- land brown bread made with unbolted flour, that is, with the entire flour ; which bread, in many rich families, adorns the breakfast table. Among all the arts known to man, there is none which enjoys a juster appreciation, and the products of which are * Composition of Wheat Bran. (Millon.) (Kekule.) Starch . . 52 "0 Gluten . Sugar Fat Woody Fibre Salts . Water 14-9 } 67-3 1-0 3-6 4-1 9-7 9-2 5-0 5-6 13-8 13-8 100-0 100-0 H H 466 LETTERS ON CHEMISTRY. more universally admired, than that which is concerned in the preparation of our food. Led by an instinct, almost approaching to intelligence, as the unerring guide, and by the sense of taste, which protects the health, the experienced cook, with respect to the choice, the admixture, and the pre- paration of food, has made acquisitions surpassing all that chemical and physiological science have done in regard to the doctrine or theory of nutrition. In soup and meat sauces, he imitates the gastric juice ; and by the cheese which closes the banquet, he assists the solvent action of the epithelium of the stomach. The table, supplied with dishes, appears to the observer like a machine, the parts of which are harmo- niously fitted together, and so arranged, that, when brought into action, a maximum of effect may be obtained by means of them. The able culinary artist accompanies the sanguige- nous matter with those which promote the process of solution and sanguification, in due proportion ; he avoids all kinds of unnecessary stimuli, such as do not act in restoring the equi- librium ; and he provides the due nourishment for the child and for the old man, as well as for both sexes. The intelligent and experienced mother, or nurse, chooses food for the child with the same attention to the laws of nature ; she gives him chiefly milk and farinaceous food, always adding fruits to the latter ; she prefers the flesh of adult animals which is rich in bone earth, to that of young animals, and always accompanies it with garden vegetables ; she gives the child especially bones to gnaw,* and excludes from its diet veal, fish, and potatoes ; to the excitable child of weak digestive powers, she gives, in its farinaceous food, infusion of malt, and uses milk-sugar, the respiratory matter prepared by nature herself for its respiratory process,t in preference to cane-sugar j and she allows him the unlimited use of salt. * In Upper Hesse, near Giessen, the peasantry use, as an exceljent domestic remedy in the teething of children, pure lime-water, which the little creatures eagerly take, a teaspoonful at a time. t In the cheese dairies of England thousands of cwts. of this valuable respiratory matter are annually lost in the wliey. EFFECTS OF VARIATIONS IN DIET. 467 The unequal effects of different kinds of food, with regard to the bodily and mental functions of men, and the depend- ence of these on chemical and physiological causes, are indis- putable ; but as yet the attempt has hardly been made to explain these differences according to the rules of scientific research. Many writers maintain that flesh and bread contain phos- phorus, that milk and eggs contain a phosphorised fat like brain, and that the origin, and, consequently, the activity of the matter of the brain is connected with this phosphorised fat. Hence no excess of phosphorus can be supposed, for example, to exist in thinkers (because they consume much phosphorus) ; and it is a certain truth that there is no thought without phosphorus ! (See " Lehre der Nahrungs- mittel fur das Volk. von Dr. Jac. Moleschott. Erlangen." 1850, p. 116.) But no evidence is known to science, tending to prove that the food of man and animals contains phos- phorus as such, in a form analogous to that in which sulphur occurs in it. It has long been proved that the cause of the amount of phosphoric acid obtained by the incineration of animal matters, or of food, being less than may be detected in the moist way, is merely due to the loss of a certain por- tion of the phosphoric acid, decomposed and volatilised by the combined action of heat and charcoal ; and that this loss may be entirely prevented by the addition of alkalies or alkaline earths, which combine with and retain the free phosphoric acid. No one has ever yet detected phosphorus in any fat of the body, of the brain, or of the food, in any other form than that of phosphoric acid. The notion that such other compounds of phosphorus exist in the body, and that their presence is connected with the production of thoughts in the human brain, proceeds generally from ama- teurs in science, and rests on superficial observations, without the slightest scientific foundation. It is certain that three men, one of whom has had a full meal of beef and bread, the second cheese or salt fish, and the third potatoes, regard a difficulty which presents itself from entirely different points of view. The effect of the H u 2 468 LETTERS ON CHEMISTRY. different articles of food on the brain and nervous system is different, according to certain constituents peculiar to each of these forms of food. A bear, kept in the anatomical department of the university of Giessen, exhibited a very gentle character as long as he was fed exclusively on bread. A few days of feeding with flesh rendered him savage, prone to bite, and even dangerous to his keeper. It is well known that the vis irascibilis of swine may be so exalted by feeding them with flesh, that they attack men. The carnivora are, in general, stronger, bolder, and more pugnacious than the herbivorous animals on which they prey ; in like manner, those nations which live on vegetable food differ in disposition from such as live chiefly on flesh. If the strength of individuals consist of the sum of the effects of force which they can exert, without injury to health, in order to overcome resistance, this obviously has a direct ratio to the plastic matters in their food. Those nations which feed on wheat and rye are, in this sense, stronger than those whose food is potatoes and rice ; and these again are stronger than the negroes, who feed on couscous, manioc, cassava, or taro. The relations of the respiratory matters in food are different. These are chiefly distinguished by the rapidity and the per- manence of their effects. Hours must elapse before all the starch of bread, in the stomach and intestines, has become soluble, so as to enter the blood and be employed in the respiratory process. Milk- sugar and grape-sugar require no preparation by the digestive organs, and thus enter the blood more rapidly. The effect of fat is the slowest in being produced, but it lasts much longer. Of all respiratory matters, alcohol acts most rapidly. Wine, and fermented vegetable juices in general, differ from spirits in containing alkalies, organic acids, and certain other substances, which it is the business of chemistry more espe- cially to ascertain. Beer is an imitation of wine. Brandy (whisky, rum) consists of water and one of the ingredients of wine. VALUE OF WINES. 469 In virtue of its characteristic ingredients, wine unites in its composition a number of conditions, by which, in the human body, the consequences on the nervous system of the action of alcohol which exalts the functions of the brain and spinal chord, are, after a certain time, more or less com- pletely neutralised. Bad effects, therefore, much less fre- quently follow the use of wine than of alcohol. The commercial value of wine is directly proportional to its immediate effects, and inversely proportional to its dis- agreeable after-effects (called in Germany, Katsenjammer). Other things being the same, its price is higher the more perfectly its effects are rendered harmless by a corresponding increase in the secretions of the lungs and of the kidneys. The alcohol is always considered in fixing the prices, but in the nobler wines, the price bears no ratio to the amount of alcohol, but is rather in proportion to that of the fixed ingredients.* The flavour or bouquet of wine has only in so far an influence on its price as it is an index to all its effects taken together. The nobler wines of the Rhine, and many of those of Bor- deaux, are distinguished above all others by producing a minimum of injurious after-effect. The quantity of wine consumed on the Rhine by persons of all ages, without per- ceptible injury to their mental and bodily health, is hardly credible. Gout and calculous diseases are nowhere more rare than in the district of the Rheingau, so highly favoured by nature. In no part of Germany do the apothecaries' establishments bring so low a price as in the rich cities on the Rhine ; for there wine is the universal medicine for the * Arranged according to price, the following Rhenish wines contain : Of Alcohol. Of solid residue. Steinberger 1846 . . 10-87 . . 10-55 Marco brunner Hatteuheimer Steinberger 1822 Riidesheiiner Marcobrunner Geisenheiiner 11-14 1071 10-87 12-61 11-6 126 5 18 > Fresenuis. 4-2 L 994 539, . 5-10 1 Gre 'S er ' 3-06 470 LETTERS ON CHEMISTRY. healthy as well as the sick, it is considered as milk for the aged (see Appendix). Alcohol stands only second to fat as a respiratory material. Its use is attended with a corresponding diminution in the starch and sugar of our food, and is irreconcileable with that of fat.* Alcohol and alcoholic drinks are from their price most costly materials of respiration. The same effect could be produced in the body by means of saccharine and farinaceous articles of food at one-fourth to one-fifth of the cost. As in the case of plants and animals, so in man, the food should be of an indifferent character ; it should exert neither a chemical nor peculiar action on the healthy frame, by which its normal functions are either excited or retarded. From this point of view, the use of wine is quite superfluous to man ; for even though it be not always injurious to health, yet it is constantly followed by the expenditure of power. These drinks promote the change of matter in the body, and are consequently attended by an inward loss of power, which ceases to be productive, because it is not em- ployed in overcoming outward difficulties, i.e., in working. * Persons accustomed to the use of wine, when they take cod-liver oil, soon lose the taste and inclination for wine. Since the establishment of Temperance or Abstinence Societies, it was thought fair, in many English families, to compensate in money those ser- vants who took the pledge and no longer drank beer, for the former daily allowance of beer ; but it was soon found that the monthly consumption of bread increased in a striking degree, so that the beer was twice paid for ; once in money, and a second time in its equivalent of bread. On the occasion of the meeting of the Peace Congress in Frankfort, the proprietor of the celebrated H6tel de Russie told me, with expressions of astonishment, that at his table at that time, a regular deficiency occurred in certain dishes, especially farinaceous dishes, puddings, &c. ; an unheard of occurrence in a house in which the amount and proportion of the dishes for a given number of persons has been for years fixed and known. This dining-hall was filled with friends -of peace, all of whom belonged to tem- perance unions, and drank no wine. Herr Sarg observed, that those who take no wine always eat more in proportion. In wine countries, therefore, the price of the wine is always included in that of the dinner, and it is considered just that in hotels people should pay for wine, even when' they drink none. " monstrous ! but one halfpennyworth of bread to this intolerable deal of sack ! " Shakspere. USE OF ARDENT SPIRITS. 471 In many places destitution and misery have been ascribed to the increasing use of spirits. This is an error. The use of spirits is not the cause, but an effect of poverty. It is an exception from the rule when a well-fed man becomes a spirit- drinker. On the other hand, when the labourer earns by his work less than is required to provide the amount of food which is indispensable in order to restore fully his working power, an unyielding, inexorable law or necessity compels him to have recourse to spirits. He must work ; but in consequence of insufficient food, a certain portion of his working power is daily wanting. Spirits, by their action on the nerves, enable him to make up the deficient power at the expense of his body, to consume to-day that quantity which ought naturally to have been employed a day later. He draws, so to speak, a bill on his health, which must be always renewed, because, for want of means, he cannot take it up ; he consumes his capital instead of his interest ; and the result is the inevitable bankruptcy of his body. Tea, coffee, and chocolate differ from wine in their action on the vital processes. If we consider that in Europe and America more than eighty million pounds of tea, and in the Customs' Union more than sixty million pounds of coffee are annually con- sumed ; that in England and America tea forms part of the daily arrangements of the poorest labourer, as well as of the richest landowner ; that in Germany the people in the country and in towns adhere the more tenaciously to coffee, the more the abundance and choice of food is limited by their poverty ; and that the lowest wages are always divided into a portion for coffee, and another for bread and potatoes : when we reflect on these facts it is impossible to admit the assertion, "that the use of coffee and tea is a matter of mere habit." (Knapp, Die Nahrungsmittel. Brunswick, 1847.) It is true that thousands have lived without a knowledge of tea or coffee, and daily experience teaches that under certain circumstances they may be dispensed with without disadvantage to the merely animal vital functions. But it is an error, certainly, to conclude from this that they may be 472 LETTERS ON CHEMISTRY. altogether dispensed with in reference to their effects ; and it is a question whether, if we had no tea and no coffee, the popular instinct- would not seek for and discover the means of replacing them. Science, which accuses us of so much in these respects, will have in the first place to ascertain whether it depend on sensual and sinful inclinations merely, that every people of the globe has appropriated some such means of acting on the nervous life ; from the shore of the Pacific, where the Indian retires from life for days in order to enjoy the bliss of intoxication with koka, to the Arctic regions, where Kamtschat dales and Koriakes prepare an intoxicating beverage from a poisonous mushroom. We think it, on the contrary, highly probable, not to say certain, that the instinct of man, feeling certain blanks, certain wants of the intensified life of our times, which can- not be satisfied or filled up by mere quantity, has discovered, in these products of vegetable life, the true means of giving to his food the desired and necessary quality. Every substance, in so far as it has a share in the vital processes, acts in a certain way on our nervous system, on the sensual appetites and the will of man. Macaulay, the distinguished inquirer in the province of history, has indeed, in his classical work, bestowed a well merited attention on the influence of coffee-houses on the political condition of England in the seventeenth century, but the share which the constituents of coffee then had in determining the direction of mental activity is a problem which has yet to be solved. What we know of the physiological effects of these drinks is not worth mentioning. These effects are usually ascribed to the presence of theine (identical with the caffeine in coffee, and found also in Mate or Paraguay tea), and this is probably correct. There are no drinks, which in their complexity and in the nature of certain constituents, have more resemblance with soup than tea and coffee, and it is very probable that the use of them as a part of food depends on the exciting and vivifying action which they have in common with soup. ACTION OF ORGANIC BASES ON THE SYSTEM. 473 When common tea leaves are placed on a watch-glass, loosely covered with paper and heated on a hot iron plate gradually to the point at which browning takes place, long white shining crystals appear on the paper and on the surface of the leaves. This is theine. By its properties theine belongs to the class of the organic bases, all of which, without exception, have an action on the nervous system. If arranged in a series, beginning with theine, the bodies at the end of the scale, strychnine and brucine, act as the most frightful poisons ; quinine, standing near the middle, is a highly prized remedy ; the constituents of opium have, in certain doses, medicinal effects, in larger doses they are poisonous. The medicinal and poisonous organic bases contain, for one equivalent of nitrogen, more than eight equivalents of carbon. Theine or caffeine, and the bodies resembling them, which may be taken without injury, all, on the other hand, contain, for the same amount of nitrogen, less carbon than the constituents of blood (8 equivalents). Theine is related, in composition, to no organic nitrogenous base more closely than to kreatinine, that remarkable com- pound, produced in the vital process, and occurring in the muscular system of animals ; and to glycocoll, which we may suppose to exist in gelatine coupled with another compound as may be seen by the following formulae : Theine C N H 0, Kreatinine .... Glycocoll (anhydrous) Kreatine ..... Theobromine (in Cacao) . . . . C 8 N 3 H 7 2 . C 8 N 2 H 8 6 . . . C 8 N 3 H U 6 . . . C 7 N 2 H 4 3 We see, by these formulae, that kreatinine contains the elements of theine and those of amide (NH 2 ), and that glycocoll and kreatine differ in this, that the latter contains 1 eq. of ammonia more than the former. Theine yields, in certain processes of decomposition, a series of most remarkable products, which have much analogy with those derived from uric acid in similar circumstances. (Rochleder.) The infusion of tea differs from that of coffee 474 LETTERS ON CHEMISTRY. by containing iron and manganese. If we evaporate to dry- ness a clear infusion of Pekoe or Souchong tea, and incinerate the residue perfectly, there is left an ash, which is often green from manganate of potash, and gives off chlorine when treated with hydrochloric acid in consequence of the presence of manganic acid. The presence of these metals in tea is the more remarkable, because the most delicate tests do not detect the iron in tea ; if a salt of iron be added, the tea becomes black, like ink, on account of the presence of tannic acid. Infusion of tea contains a compound of iron, on which tannine obviously has no action. We have, therefore, in tea (of many kinds) a beverage which contains the active constituents of the most powerful mineral springs, and however small the amount of iron may be, which we daily take in this form, it cannot be destitute of influence on the vital processes.* By the presence of empyreumatic substances, roasted coffee acquires the property of checking those processes of solution * An infusion of 70 grammes of Pekoe tea contained 0*104 grammes of peroxyde of iron, and 0-20 grammes of protoxide of manganese. (Fleit- mann.) Constituents of the Ashes of Infusion of tea. Decoction of Coffee. Cacao Beans. Souchong. . Java Coffee. Guayaquil Cacao. (Lehmann). (Lehmann.) (Zedeler.) Potash 47-45 51-45 37 '14 Lime Peroxide of iron . Phosphoric acid Sulphuric acid . Silicic acid . Carbonic acid . Oxide of manganese Chloride of sodium Soda . Charcoal and Sand 1-24 3-58 2-88 6-84 8-67 15-97 3-29 0-25 0-10 9-88 1002 39-65 8-72 4-01 1-53 2-31 0-73 0-17 10-09 20-50 0-71 3-62 KC1 1-98 Cl 1'66 5-03 ,, ,, 1-09 0-49 100-27 100-68 99-10 100 parts of the leaves (Souchong) extracted by boiling water give 15*536 parts of dried extract, which yield 3'06 of ashes (=19 '69 per cent, of the extract); 100 parts of roasted coffee yielded by decoction with water, 21 '52 parts of extract, which gave 3'4l of ashes ( lb' - 6 per cent, of the extract); the cacao beans were shelled, and gave 3'62 per cent, of ashes. COFFEE CHECKS DIGESTION". 475 and decomposition which are begun and kept up by ferments. We know that all empyreumatic bodies oppose fermentation and putrefaction ; and that, for example, smoked flesh is less digestible than that which is merely salted. Persons of weak or sensitive organs, will perceive, if they attend to it, that a cup of strong coffee after dinner instantly checks digestion. It is only when the absorption and removal of it has been effected, that relief is felt. For strong digestions, which are not sufficiently delicate reagents to detect such effects, coffee after eating serves, from the same cause, to moderate the activity of the stomach, exalted beyond a certain limit by wine and spices. Tea has not the same power of checking- digestion ; on the contrary, it increases the peristaltic motions of the intestines ; and this is sometimes shown in producing nausea, especially when strong tea is taken by a fasting person.* It has already been mentioned, that the daily consumption of respiratory matter amounts to five or six times the weight of the plastic matter, and in years of scarcity the want of the former is first and most sensibly felt by all classes of the people. While the prices of fat and butter rise with that of grain, and potatoes become even proportionally dearer than grain, the price of meat generally remains the same as in cheaper years. One reason of this is, that bread may be substituted for meat, but for the wants of man it cannot be so perfectly replaced by meat.t Another cause of the com- * According to the investigations of Doctor Julius Lehmann (Ann. der Chim. u. Ph. B. 88, s. 205), the use of coffee diminishes the excretion of urea, and consequently exercises an action in the change of matter, opposite to that of wine. t In describing his residence in the Pampas, Darwin says, in his admirable work, which contains a rich store of the finest observations: "We were able here (Tapalguen, 17th September) to buy some biscuit. I had for some days eaten only meat, and felt quite well on this diet ; but I observed that it was adapted only to a very active mode of life. I have heard that sick persons in England, put on animal diet alone, could not endure it, even with the hope of health before their eyes ; and yet the Gauchos in the Pampas, during many months, eat nothing but beef. But I must observe, that they eat a very large quantity of fat, and they despise dry, lean flesh, like that of the Agouti." (Darwin's Travels.) Homer omits no opportunity in describing the meals and feasts of his 476 LETTERS ON CHEMISTRY. paratively low price of meat depends on the circumstance, that in years of bad harvests, from an excess of moisture, should the ordinary nutritious plants fail, there is abundance of green fodder, of clover, grass, and turnips. Meat retains its lower price, because the demand for it does not increase like that for bread. In dry years the farmer has no fodder, he is forced to kill his cattle and sell them for what they will fetch, and the overstocking of the market renders meat even cheaper than in ordinary years. Man, when confined to animal food, requires for his sup- port and nourishment extensive sources of food, even more widely extended than the lion and tiger, because, when he has the opportunity, he kills without eating. A nation of hunters, on a limited space, is utterly incapable of increasing its number beyond a certain point, which is soon attained. The carbon necessary for respiration must be obtained from the animals, of which only a limited number can live on the space supposed. These animals collect from plants the constituents of their organs and of their blood, and yield them, in turn, to the savages who live by the chase alone. They, again, receive this food unaccompanied by those compounds, destitute of nitrogen, which, during the life of the animals, served to support the respiratory process. While the savage with one animal and an equal weight of starch could maintain life and health for a certain number of days, he would be compelled, if confined to flesh alone, in order to procure the carbon necessary for respiration, during the same time, to consume five such animals. His food con- tains an excess of plastic matter ; during the greater part of the year, that which is wanting is the respiratory material which ought to accompany the sanguigenous food. Hence the tendency to spirit drinking, always observed in men who live on flesh exclusively. The practical view of agriculture cannot be more clearly heroes, of singing the praise due to the "blooming" fat of the swine s back. BENEFITS OF SCIENCE. 477 or profoundly conceived than it was by the North American chief, whose speech on the subject is reported by Crkvecceur. The chief, in recommending agriculture to his tribe, the Mis- sissean Indians, said : " Do you not see that the whites live on corn, but we on flesh 1 that the flesh requires more than thirty moons to grow, and is often scarce ? that every one of the wonderful seeds, which they scatter on the soil, returns them more than a hundred-fold ? that the flesh has four legs to run away, and we only two to catch it ? that the seeds remain and grow, where the white man sows them ^ that winter, which for us is the season of laborious hunts, is to them a time of rest 1 It is for these reasons that they have so many children, and live longer than we do. I say, then, to every one who hears me, before the trees above our huts shall have died of age, before the maples of the valley cease to yield us sugar, the race of the sowers of corn will have extirpated the race of flesh-eaters, unless the hunters resolve also to sow." In his difficult and laborious life of the chase, the Indian consumes in his limbs a large sum of force ; but the effect produced is very trifling, and bears no proportion to the expense. Cultivation is the economy of force. Science teaches us the simplest means of obtaining the greatest effect with the smallest expenditure of organic power, and with given means to produce a maximum of force. The unprofitable exertion of power, the waste of force in agriculture, in other branches of industry, in science, or in social economy, is characteristic of the savage state, or of the want of true civilisation. Herein consists, in fact, the extraordinary superiority of power, which distinguishes our period from all earlier times ; in this, namely, that the development of the natural sciences and of mechanics, and the study of all the causes which produce mechanical motion and change of place, have led to the more accurate acquaintance with the laws which enable men to convert into willing and obedient servants those natural forces which formerly excited fear and terror. Like a Prometheus, man, with the aid of the divine spark 478 LETTERS ON CHEMISTRY. from above, which, when fed by religion and morality, is the foundation of all mental improvement, has infused life into the elements of the globe. The steam-engine receives food and drink, and breathes like an animal ; in its body there exists a source of heat and a source of power, by means of which internal and external effects of motion are produced ; the most perfectly trained horse does not more patiently obey man's will, than the locomotive of our railways, which goes fast or slow, stands still and obeys the lightest touch of his fingers. Science, which causes machinery to do the work formerly done by slaves, has established a more just proportion between the forces of external nature and the organic force.* The sum of the rays of light and heat which the earth receives from the sun, is a fixed value, but it is unequally distributed on the earth's surface, in consequence of causes which must be named providential. Hence, there is at one place an excess, which increases the production of the con- ditions essential to life ; at another there is a deficiency, which causes that production to fall off. If the channels exist, through which these forces may flow both ways, an equilibrium is spontaneously effected ; there is nowhere excess, and nowhere deficiency. In like manner riches, and its shadow, poverty, are distributed over the earth. At all times the relative pro- * The chaste queen of Ithaca, in the absence of her lord, Ulysses, re- quired, as Homer tells us, twelve female slaves, who laboured day and night, to grind the corn necessary for the support of her household. It was a simple family economy, and I exaggerate in assuming that Penelope had to feed, daily, three hundred people. In these circumstances, there- fore, where all labour was performed in the sweat of man's brow, one person was required to grind corn for twenty-five, perhaps for only half that number. In our days the grinding of corn employs far fewer hands. In the mill at St. Maur, near Paris, the grain for a hundred thousand soldiers can be ground every day by twenty workmen ; that is, one labourer for five thousand consumers. Penelope could only give, doubt- less, a very meagre pay to her twelve slaves, although overwhelmed with labour, because the produce of that labour was relatively so small. (Chevallier. Lettres sur 1' Organisation du Travail, Paris. Capelle, 1848, p. 29.) BALANCE OF NATURE. 479 portion of them has been the same and unchangeable. Any- permanent increase in wealth is opposed by circumstances, which set a limit to it. As the blood moves from the great arterial trunks towards the capillaries, so the largest income is consumed, and flows through an infinite number of smaller channels back to the original source. Where the light is strong the shadows appear darker but nature wills, that in all degrees of light, vigorous plants shall grow. Without trees there would be no underwood, no corn, and no crops, for trees attract the fertilising rain, and cause the springs perpetually to flow, which diffuse prosperity and comfort. The theories of modern socialism would have no shadow anywhere ; but if the last blade of grass which casts a shadow were destroyed, then there would indeed be light everywhere, but with it universal death, as in the desert of Sahara. By means of the forces produced in his frame, man opposes to the natural forces which strive incessantly to annihilate his existence, a resistance, which must be daily renewed, if his continuance for a season is to be secured. In every hour a portion of our body dies off, and even in the state of perfect health, the machine, after seventy or eighty years, becomes the prey of the inorganic powers ; all resistance ceases; the elements of the machine return to the atmosphere and to the soil. Life is a continual struggle with the forces of Nature, a constant alternate disturbance and restoration of a state of equilibrium. Man requires, in the form of food and drink, the means of producing force and heat ; he thus creates in his body the resistance which he must oppose to the action of the atmosphere, which daily takes up a part of his organism. In order to preserve his temperature, and to protect him against the weather, he requires a dwelling, clothing, and fire ; in order to preserve health, he must have the means of insuring personal cleanliness, and to restore it, he must have medicine. Food and drink can, to a certain extent, represent and replace clothing, fire, and medicine ; but they themselves are not replaceable by the supply of any of the 480 LETTERS ON CHEMISTRY. other wants of life they are absolute or indispensable necessaries. When there is a want of internal resistance, as in starva- tion, the same natural forces, which determine the vital phenomena, act like a sword, which gradually but irresistibly penetrates to the central point of life, and puts an end to its activity. Man requires, for the development, perfection, and pre- servation of the peculiar actions of his organs of sense, certain other conditions, the necessity for which leads him to pursue the agreeable and the profitable. Besides these, man has still a number of other wants, arising from his intellectual nature, which are not satisfied by means of natural forces. Such are the manifold conditions of the intellectual functions, on the development, perfection, and preservation of which depend the due and judicious application of his bodily powers, as well as the bending and employment of the natural forces to satisfy all his wants, whether those which are essential to life, or those which are profitable and agreeable only. As in the body of an individual, so also in the sum of all individuals, which constitutes the state, there goes on a change of matter, which is a consumption of all the conditions of individual and social life. Silver and gold have to perform in the organism of the state the same function as the blood corpuscles in the human organism. As these round discs, without themselves taking an immediate share in the nutritive process, are the medium, the essential condition of the change of matter, of the production of' the heat and of the force by which the temperature of the body is kept up, and the motions of the blood and all the juices are determined, so has gold become the medium of all activity in the life of the state. During the Middle Ages, the tax-payer paid his imposts in corn, wine, eggs, and fowls, and in feudal services and labour ; all the necessaries of life he produced for himself. Colonial wares were unknown to him, and, with half a pound of copper coin, he procured the tools he required. The THE STATE ANALOGOUS TO THE BODY. 431 municipal communities had their common breweries, and in many places the authorities bought wine, and retailed it to the citizens. Gold and silver were, for the great majority, goods which they wore ostentatiously on their clothes or furniture. But since gold has assumed, in the organism of the state, a function corresponding to the conveyance of oxygen in the body, the rich use, in place of the massive vessels of silver and gold formerly so common, copper or white brass, plated with silver and gold. The change of matter, in the state, as in the body, is the source of all its powers ; its continued existence depends on the restoration of the wasted materials, on the renovation or restoration of all the conditions of individual or social life. As in the animal body the change of matter may be measured by the number of blood corpuscles, which in a given time pass from the heart to the capillaries and from those back to the heart, so may the change of matter in the state be measured by the rapidity with which money passes from hand to hand. All causes which impede this motion, or which act on the change of matter, on waste and supply, as the natural forces do in the body, disturb the equilibrium, and pro- duce peculiar conditions analogous to the diseases of the individual. Compared with the effects produced by the rapidity of the circulation of money, its absolute quantity is almost nothing. The body of the state, in perfect health, is like the human body, through the heart and capillaries of which, in twenty- four hours, from 31,000 to 38,000 Ibs. of blood pass, while the absolute amount of the blood is a thousand times smaller. The sum of all the resistances, opposed by Nature to the continuance of life and to the acquisition of the conditions of life (which, with regard to the peculiar function of money, is equivalent to the acquisition of money), is precisely so great, that the active power producible in man can come into equilibrium with it. Man, according to the laws of Nature, cannot, without endangering his continued existence, consume any part of his force in overcoming resistances, if- i i 482 LETTERS ON CHEMISTRY. he does not obtain by their removal the means of restoring his wasted powers. A relation perfectly analogous exists in the organism of the state. Every waste of power, which does not serve for the reproduction of a condition essential to the life of the state, or the non-employment of power, which exists and may be employed to produce a condition of vitality, disturbs the health of the political body. Just as every muscular fibre, every nerve, every part of a tissue in the animal body, has a share in the change of matter going on in it, and contributes its part to the pre- servation and continuance of the general processes of digestion, sanguification, motion of the juices, and secretion, as well as of all the actions of the limbs, the senses, and the brain, so must every individual in the state, according to the measure of the available force in his limbs, senses, or mind, contribute his share to the preservation and restoration of the vital phenomena in the general body. The effect of these forces is what we call labour. Every part of the organism has a right to the freest use of its power of labour; and all have a right to labour, unimpeded and unchecked by others. The maximum of effect from the powers of labour, is inversely proportional to the sum of the resistance to be overcome ; the greater the resistance, the less is the effect. The duty of a Christian state is to diminish, not to increase, the resistance or the obstacles which exist ; but the doctrines of the greatest statesman of our time * of that wise and large hearted man, whose loss the nation to whom he belonged and the world will mourn for a century to come appear, up to this time, to have found a congenial and fertile soil neither in the understanding nor in the hearts of men. It is ignorance of the conditions which determine the health, the prosperity, and the power of the State, which has caused the mispro- portions which in many states are the source of so many evils. Instead of a harmonious whole, we have an abortion, * Sir Robert Peel. CERTAINTY OF NATURAL LAWS. 433 a huge head on a dwarfish body; enormous arms, and thin, feeble legs ; a large stomach, and small lungs. When accident and caprice, instead of foresight and reflection, or old customs, at war with the laws of nature, are allowed to regulate the motions and the expenditure of power in the organism of the State, the natural results are feebleness and defects, and, in their train, poverty and misery. Thus a barbarous state, by means of unjust and unequally dis- tributed imposts, urges whole masses of the population, during their entire life, towards famine ; compelling them to expend too great a sum of their own force, merely to prolong their existence, and for other objects, by which the powers of all the individual parts are not perfectly restored. Thus states with great standing armies have only the appearance of strength, because a perpetual phlebotomy abstracts the best part of their blood, and their noblest juices. Their strength is like that which the savage finds in the intoxication of alcohol : when the intoxication has passed away, the power has fled with it. " All those things which appear to be left to the free-will, the passions, or the degree of intelligence of men, are regulated by laws as fixed, immutable, and eternal as those which govern the phenomena of the natural world. No one knows the day or the hour of his own death ; and nothing appears more entirely accidental than the birth of a boy or of a girl in any given case. But how many, out of a million of men living together in one country, shall have died in ten, twenty, forty, or sixty years, how many boys and girls shall be born in a million of births, all this is as certain, nay, much more certain, than any human truth. " The statistics of courts of justice have disclosed to us the regular repetition of the same crimes, and have esta- blished the fact, incomprehensible to our understandings, because we do not know the connecting links, that in every large country, the number of offences, and of each kind of oifence, may be predicted for every coming year with the same certainty as the number of the births and of the natural deaths. Of every 100 persons, accused before the i i 2 484 LETTERS ON CHEMISTRY. supreme tribunal in France, 61 are condemned ; in England, 71. The variations, on an average, amount hardly to the -P^ part of the whole. We can predict, with confidence, for fifteen years to come, the number of suicides generally. that of the cases of suicide by fire-arms, and that of the cases of suicide by hanging. " Every large number of phenomena of the same kind which rise and fall periodically, leads to a fixed proportion. This is the law of large numbers, to which all things and all events, without exception are subject. These laws have nothing to do with the essence of vice and virtue in the moral world, but with the external causes, and the effects they produce in human society. No one denies the influence of education, and of habits of order and labour on the conduct of men, but no one thinks of regarding this moral conduct as a mere result of those habits. Good education, and improved cultivation, diminish the number of offences, as well as that of the annual deaths in our tables of mortality." * It is plain, that a knowledge of the true means of bringing human society nearer to a better condition, and of giving a permanent foundation to the happiness of nations, can only be attained by studying the influence of all other arrangements, customs, habits, and institutions, on the morality of mankind, according to the numerical method. This constitutes true natural science. * Quetelet "On Man and the Development of his Powers." German translation by Riecke. Stuttgard, 1838. ORGANIC LIFE IN THE OCEAN. 485 LETTER XXXIII. Organic Life in the Ocean The water yields Sea-plants all their elements Function of the Soil in Vegetation ; to furnish the Mineral elements to Plants The Soil is exhausted if the Minerals removed by Crops are not restored by Animal mamires, bone earth, &c. Causes of the luxu- riant growth of Tropical Plants Perennial Plants and Trees require less Mineral food than Annuals Explanation of the effects of Drought on the lower leaves of Plants. EVERY one knows that in the immense, yet limited expanse of the ocean, whole worlds of plants and animals succeed each other ; that one generation of these animals receive all their elements from plants, which, after their death, are again given up in their original form, to serve as nourishment to a new generation of plants. The oxygen which marine animals withdraw in their respir- ation from the air, dissolved in sea water, is returned to the water by the vital processes of sea plants ; that air is richer in oxygen than atmospheric air, containing 32 to 33 per cent., while the latter contains only 21 per cent. This oxygen now combines with the products of the putrefaction of dead animal bodies, changes their carbon into carbonic acid, their hydrogen into water, while their nitrogen assumes again the form of ammonia. Thus we observe that in the ocean a circulation takes place without the addition or subtraction of any element, unlimited in duration, although limited in extent, inasmuch as in a confined space the nourishment of plants exists in a limited quantity. We well know that marine plants cannot derive a supply of humus for their nourishment through their roots. Look at the great sea-tang, the Fucus giganteus : this plant, according to Cook, reaches a height of 360 feet, and a single 486 LETTERS ON CHEMISTRY. specimen, with its immense ramifications, nourishes thousands of marine animals, yet its root is a small body, no larger than the fist. What nourishment can this draw from a naked rock, upon the surface of which there is no perceptible change 1 It is quite obvious that these plants require only a hold, a fastening to prevent a change of place, as a counterpoise to their specific gravity, which is less than that of the medium in which they float. That medium provides the necessary nourishment, and presents it to the surface of every part of the plant. Sea- water contains not only carbonic acid and ammonia, but the alkaline and earthy phosphates and carbonates required by those plants for their growth, and which we always find as constant constituents of their ashes. All experience demonstrates that the conditions of the existence of marine plants are the same which are essential to terrestrial plants. But the latter do not live like sea- plants, in a medium which contains all their elements, and surrounds with appropriate nourishment every part of their organs ; on the contrary, they require two media, of which one, namely, the soil, contains those essential elements which are absent from the medium surrounding them, i. e. the atmosphere. Is it possible that we could ever be in doubt respecting the office which the soil and its component parts subserve in the existence and growth of vegetables? that there should have been a time when the mineral elements of plants were not regarded as absolutely essential to their vitality 1 Has not the same circulation been observed on the surface of the earth which we have just contemplated in the ocean, the same incessant change, disturbance, and restoration of equilibrium ? Experience in agriculture shows that the production of vegetables on a given surface increases with the supply of certain matters, originally part of the soil which had been taken up from it by plants the excrements of man and animals. These are nothing more than matters derived from vegetable food, which in the vital processes of animals, PRINCIPLES OF A RATIONAL AGRICULTURE. 487 or after their death, assume again the form under which they originally existed, as parts of the soil. Now, we know that the atmosphere contains none of these substances, and therefore can replace none ; and we know that their removal from a soil destroys its fertility, which may be restored and increased by a new supply. Is it possible, after so many decisive investigations into the origin of the elements of animals and vegetables, the use of the alkalies, of lime and the phosphates, that any doubt can exist as to the principles upon which a rational agriculture depends 2 Can the art of agriculture be based upon anything but the restitution of a disturbed equilibrium ; Can it be imagined that any country, however rich and fertile, with a flourishing -commerce, which for centuries exports its produce in the shape of grain and cattle, will maintain its fertility, if the same commerce does not restore, in some form of manure, those elements which have been removed from the soil, and which cannot be replaced by the atmosphere 1 Must not the same fate await every such country which has actually befallen the once prolific soil of Virginia, now in many parts no longer able to grow its former staple productions wheat and tobacco 1 In the large towns of England the produce both of English and foreign agriculture is largely consumed; ele- ments of the soil indispensable to plants do not return to the fields, contrivances resulting from the manners and customs of English people, and peculiar to them, render it difficult, perhaps impossible, to collect the enormous quan- tity of the phosphates which are daily, as solid and liquid excrements, carried into the rivers. These phosphates, although present in the soil in the smallest quantity, are its most important mineral constituents. It was observed that many English fields exhausted in that manner imme- diately doubled their produce, as if by a miracle, when dressed with bone earth imported from the Continent. But if the export of bones from Germany is continued to the extent it has now reached, our soil must be gradually exhausted, and the extent of our loss may be estimated, by 483 LETTERS ON" CHEMISTRY. considering that one pound of bones contains as much phos- phoric acid as a hundred-weight of grain. The imperfect knowledge of Nature and of the properties and relations of matter possessed by the alchemists gave rise, in their time, to an opinion that metals as well as plants could be produced from a seed. The regular forms and ramifications seen in crystals, they imagined to be the leaves and branches of metallic plants ; and as they saw the seed of plants grow, producing root, stem and leaves, and again blossoms, fruit and seeds, apparently without receiving any supply of appropriate material, they deemed it worthy of zealous inquiry to discover the seed of gold, and the earth necessary for its development. If the seeds of metals were once obtained, might they not entertain hopes of their growth ? Such ideas could only be entertained when nothing was known of the atmosphere, and its participation with the earth, in administering to the vital processes of plants and animals. Modern chemistry indeed produces the elements of water, and, combining them, forms water anew ; but it does not create those elements it derives them from water ; the new formed artificial water has been water before. Many of our farmers are like the alchemists of old, they are searching for the miraculous seed, which, without any further supply of nourishment to a soil scarcely rich enough to support the natural sprinkling of indigenous plants, shall produce crops of grain a hundred-fold. The experience of centuries, nay, of thousands of years, is insufficient to guard men against these fallacies ; our only security from these and similar absurdities must be derived from a correct knowledge of scientific principles. In the first period of natural philosophy, organic life was supposed to be derived from water only ; afterwards, it was admitted that certain elements derived from the air must be superadded to the water; but we now know that other elements must be supplied by the earth, if plants are to thrive and multiply. The amount of materials contained in the atmosphere, FOOD OF PLANTS IN THE AIR AND SOIL. 489 suited to the nourishment of plants, is limited ; but it must be abundantly sufficient to cover the whole surface of the earth with a rich vegetation. Under the tropics, and in those parts of our globe where the most general conditions of fertility exist, a suitable soil, a moist atmosphere, and a high temperature, vegetation is scarcely limited by space ; and, where the soil is wanting, the decaying trees, their bark and branches, become themselves the seat of vegetation and a soil for other plants. It is obvious there is no deficiency of atmospheric nourishment for plants in those regions, nor are these wanted in our own cultivated fields. The incessant motions of the atmosphere convey to all plants a like quantity of the atmospheric food neces- sary for their growth. The air between the tropics contains no more than that of the arctic zones ; and yet how different appears the amount of produce of an equal surface of land in the two situations. This is easily explicable. All the plants of tropical climates, the oil and wax palms, the sugar-cane, &c., contain only a small quantity of the sanguigenous bodies necessary to the nutrition of animals, as compared with our cultivated plants. The tubers of the potato in Chili, its native country, where the plant resembles a shrub, if collected from an acre of land, would scarcely suffice to maintain an Irish family for a single day (Darwin). The result of cultivation in those plants which serve as food, is to produce in them those constituents of the blood. In the absence of the elements essential to these in the soil, starch, sugar, and woody fibre, are perhaps formed ; but no vegetable fibrine, albumen, or caseine. If we intend to produce on a given surface of soil more of these latter matters than the plants in their uncultivated and normal state can obtain from the atmosphere or receive from the soil of the same surface, we must create an artificial atmos- phere, we must add the required elements to the soil. The nourishment which must be supplied in a given time to different plants, in order to admit a free and unimpeded growth, is very unequal. 490 LETTERS ON CHEMISTRY. On dry sand, on pure calcareous soil, on naked rocks, only a few genera of plants prosper, and these are, for the most part, perennial plants. They require, for their slow growth, only such minute quantities of mineral substances as the soil can furnish, which may be totally barren for other species. Annual, and especially summer plants, grow and attain their perfection in a comparatively short time ; they, therefore, do not prosper on a soil which is poor in those mineral substances necessary to their development. To attain a maximum in height in the short period of their existence, the nourishment contained in the atmosphere is not sufficient. If the end of cultivation is to be attained, we must create in the soil an artificial atmosphere of carbonic acid and ammonia; and this surplus of nourish- ment, which the leaves cannot appropriate from the air, must be taken up by the corresponding organs, i. e. the roots from the soil. But the ammonia, together with the carbonic acid, are alone insufficient to become part of a plant destined to the nourishment of animals. Without the alkalies, no albumen, without the alkaline and earthy phosphates, no vegetable fibrine, no vegetable caseine, can be formed. The phosphoric acid of the phosphate of lime indispensable to the cerealia and other vegetables in the formation of their seeds, is separated as an excre- ment, in great quantities, by the rind and barks of ligneous plants. How different are the evergreen plants, the cacti, the mosses, the ferns, and the pines, from our annual grasses, the cerealia and leguminous vegetables ! The former, at every time of the day during winter and summer, obtain carbon through their leaves by absorbing carbonic acid which is not furnished by the barren soil on which they grow ; water is also absorbed and" retained by their coriaceous or fleshy leaves with great force. They lose very little by evaporation, compared with other plants. On the other hand, how very small is the quantity of mineral substances which they withdraw from the soil during their almost con- stant growth in one year, in comparison with the quantity DECAY OF LEAVES IN DRY YEARS. 491 which one crop of wheat of an equal weight receives in three months ! It is by means of moisture that plants receive the neces- sary alkalies and salts from the soil. In dry summers a phenomenon is observed, which, when the importance of mineral elements to the life of a plant was unknown, could not be explained. The leaves of plants first developed and perfected, and therefore nearer the surface of the soil, shrivel up and become yellow, lose their vitality, and fall off while the plant is in an active state of growth, without any visible cause. This phenomenon is not seen in moist years, nor in evergreen plants, and but rarely in plants which have long and deep roots, nor is it seen in perennials, save in autumn and winter. The cause of this decay is now obvious. The perfectly- developed leaves absorb continually carbonic acid and am- monia from the atmosphere, which are converted into ele- ments of new leaves, buds, and shoots ; but this metamor- phosis cannot be effected without the aid of the alkalies, and other mineral substances. If the soil is moist, the latter are continually supplied to an adequate amount, and the plant retains its lively green colour ; but if this supply ceases, from a want of moistnre, to dissolve the mineral elements, a separation takes place in the plant itself. The mineral con- stituents of the juice are withdrawn from the leaves already formed, and are used for the formation of the young shoots ; and as soon as the seeds are developed, the vitality of the leaves completely ceases. These withered leaves contain only minute traces of soluble salts, while the buds and shoots are very rich in them. On the other hand, it has been observed that, where a soil is too highly impregnated with soluble saline materials, these are separated upon the surface of the leaves. This happens to culinary vegetables especially, whose leaves become covered with a white crust. In consequence of these exudations the plant sickens, its organic activity decreases, its growth is disturbed ; and if this state continues long, the plant dies. This is most frequently seen in foliaceous 492 LETTERS ON CHEMISTRY. plants, the'" large surfaces of which evaporate considerable quantities of water. Carrots, pumpkins, peas, &c., are fre- quently thus diseased, when, after dry weather, the plant being near its full growth, the soil is moistened by short showers, followed again by dry weather. The rapid evapo- ration carries off the water absorbed by the root, and this leaves the salts in the plant in a far greater quantity than it can assimilate. These salts effloresce upon the surface of the leaves, and if they are herbaceous and juicy, produce an effect upon them as if they had been watered with a solution containing a greater quantity of salts than their organism can bear. Of two plants of the same species, this disease befals that which is nearest its perfection ; if one should have been planted later, or be more backward in its development, the same external cause which destroys the one will contribute to the growth of the other. AGRICULTURE BOTH A SCIENCE AND AN ART. 493 LETTER XXXIY. Agriculture is both a Science and an Art Its objects Effects of fallowing, and of the Mechanical Operations of Agriculture. HAVING, in several of the foregoing letters, attempted to lay before you my views concerning the different kinds of food, and the purposes which they have to fulfil in the animal organism, let me now direct your attention to a scarcely less interesting and equally important subject the means of obtaining, from a given surface of the earth, the largest amount of produce adapted to the food of man and animals. Agriculture is both a science and an art. The knowledge of all the conditions of the life of vegetables, the origin of their elements, and the sources of their nourishment, forms its scientific basis. From this knowledge we derive certain rules for the exer- cise of the ART, the principles upon which the mechanical operations of farming depend, the usefulness or necessity of these for preparing the soil to support the growth of plants, and for removing every obnoxious influence. No experience, drawn from the exercise of the art, can be opposed to true scientific principles, because the latter are mere abstract expressions for the whole mass of observations from which they are deduced. Theory must correspond with experience, because it is nothing more than the reduction of a series of phenomena to their ultimate causes. A field in which we cultivate the same plant for several successive years becomes barren for that plant in a period varying with the nature of the soil : in one field it will be in three, in another in seven, in a third in twenty, in a fourth in a hundred years. One field bears wheat, and no peas ; another beans or turnips, but no tobacco ; a third gives a plentiful crop of turnips, but will not bear clover. What is 494 LETTERS ON CHEMISTRY. the reason that a field loses its fertility for one plant, the same which at first flourished there 1 What is the reason one kind of plant succeeds in a field where another fails 1 These questions belong to Science. What means are necessary to preserve to a field its fertility for one and the same plant 1 what to render one field fertile for two, for three, for all plants 1 These last questions are put by Art, but they cannot be an- swered by Art. If a farmer, without the guidance of just scientific principles, is trying experiments to render a field fertile for a plant which it otherwise will not bear, his prospect of success is very small. Thousands of farmers try such experiments in various direc- tions, the result of which is a mass of practical experience forming a method of cultivation which accomplishes the desired end for certain places ; but the same method fre- quently does not succeed, it indeed ceases to be applicable to a second or third place in the immediate neighbourhood. How large a capital, and how much power, are wasted in these experiments ! Very different, and far more secure, is the path indicated by SCIENCE ; it exposes us to no danger of failing, but on the contrary, it furnishes us with every guarantee of success. If the cause of failure of barrenness in the soil for one or two plants has been discovered, means to remedy it may readily be found. The most exact observations prove that the method of cultivation must vary with the geognostical condition of the subsoil. In basalt, graywacke, porphyry, sandstone, lime- stone, &c., are certain elements indispensable to the growth of plants, and the presence of which renders the soil fertile. This fully explains the difference in the necessary methods of culture for different places ; since it is obvious that the essen- tial elements of the soil must vary with the varieties of com- position of the rocks, from the disintegration of which they originated. Wheat, clover, turnips, for example, each require certain elements from the soil ; they will not flourish where the appropriate elements are absent. Science teaches us what EFFECTS OF FALLOW. 495 elements are essential to every species of plants by an ana- lysis of their ashes. If therefore a soil is found wanting in any of those elements, we discover at once the cause of its barrenness, but we find out at the same time how it may be removed. The empiric attributes all his success to the mechanical operations of agriculture ; he experiences and recognises their value, without inquiring what are the causes of their utility ; their mode of action ; and yet this scientific knowledge is of the highest importance for regulating the application of power and the expenditure of capital, for ensuring its economical expenditure and the prevention of waste. Can it be ima- gined that the mere passing of the ploughshare or the harrow through the soil the mere contact of the iron can impart fertility as by a charm? Nobody, perhaps, seriously entertains such an opinion. Nevertheless, the modus operandi of these mechanical operations is by no means generally understood. The fact is quite certain, that careful ploughing exerts the most favourable influence ; the surface is thus mechanically divided, changed, increased, and renovated j but the ploughing is only auxiliary to the end sought. Among the effects of time, in what in Agriculture are technically called fallows the repose of the fields are in- cluded by science certain chemical actions, which are con- tinually exercised by the elements of the atmosphere upon the whole surface of our globe. By the action of its oxygen and its carbonic acid, aided by water, rain, changes of tempe- rature, > -*i i - .v, I it L L APPENDIX. No. 1. HISTORY OF THE BOY WITH THE GOLDEN TOOTH. (Sprengel, vol. iii., 403-406. Sixteenth year.) Page 65. " A boy, ten years old, in the neighbourhood of Schweidnitz, was the miraculous child, in \vhom had grown this golden tooth. Jacob Horst, formerly physician in Schweidnitz, heard in Helmstadt, where he was at that time (15^5) professor, of this affair, and wrote a very strange book about it ; in which, without for a moment doubting the authenticity of the story, he at once regards the production of this tooth as a supernatural event, depending on the constellation under which the boy was born. On the day of his birth (22nd December, 1586), says Horst, the sun had been in the sign of Aries. By this supernatural cause, the nutritive force, in consequence of the increased heat, had been miraculously augmented, and thus, instead of bone, gold had been secreted." No. 2. Extracts from the LETTER OF GALILEO TO MAPAMA CRISTINA, GRANDDUCHESSA MADRE. Page 68. ' ' We bring forward that which is new, not to confuse nature nor the minds of men, but to enlighten them ; not to destroy science, but to give it a true foundation. But our opponents call false and heretical, that which they cannot refute, making for themselves a shield of simulated zeal for religion, and degrading the Holy Scriptures into the instrument of private opinions. But a writer ought not to be condemned unheard, when he treats not of ecclesiastical, but of natural things, and does so with the aid of reasons derived from astronomy and geometry. He who would hold in all cases to the naked grammatical sense, must needs accuse the Bible of contradictions, nay, of blasphemies, when it speaks of God's eye, his hand, or his anger. And if this take place in the apprehension of the people, how nrach the more ought we to regard it in matters which, like the natural sciences, are remote from the observation of the many, and do not affect our salvation. In these, therefore, we must not begin with the authority of the Bible, but with the observations of our senses, and the necessary proofs, because nature and the Bible alike owe their existence to God." No. 3. CRUM'S SOLUBLE ALUMINA. NOTE TO LETTER XV. Page 182. One of the most remarkable examples of metamorphosis in the pro- perties of a compound inorganic body has been discovered by Walter Crum, in Glasgow. He found that by continuous ebullition of acetate of alumina, the salt was completely decomposed, and the acetic acid volatilised. Alumina in its ordinary state is insoluble in water, very soluble in acids and alkalies, and absorbs colouring matters from solutions. But the modi- L L 2 516 APPENDIX. fi cation of alumina discovered by W. Crum is soluble in water, is entirely precipitated from a watery solution by dilute acids and alkalies, and does not form lakes with decoctions of dye-woods, but is thrown down by them in a gelatinous translucent form. Further, by concentrated acids and alkalies, the soluble alumina is again transformed into the insoluble. No. 4. CAUSE OF PUERPERAL FEVER IN THE LYING-IN-HOSPITAL, VIENNA. Page 250. "In the Lying-in Hospital here (Vienna), since there has been a division for the instruction of physicians, and a division for midwives, the number of deaths on the physicians' side was constantly greater, in 1846 even four times greater, than on that of the midwives. "It is easy to understand that so enormous a difference in the mortality in two parts of the same hospital (in 1846, for an equal number of puer- peral cases, the excess of deaths on the physicians' side was 400) attracted universal attention, and that attempts were made to detect its cause. . . . After Dr. Semmelweis, assistant on the physicians' division, had for several months considered all the circumstances, he recognised in the fact, that both he and the students occupied themselves frequently with post-mortem examinations ; that the cadaverous smell on their hands, in spite of repeated washing, does not disappear till after a considerable time, and that the pupils not unfrequently proceed to the examination of women in labour immediately after dissecting a dead body, the only possible mode by , which a putrescent animal substance could be conveyed to the genitals of the puerperal patients (which had been ascertained to be one of the prox- imate causes of the disease, of the formation of purulent matter in the blood, and in the present instance had been kept in view by Dr. S.). This was also the only one of the probable causes of puerperal disease, which either did not occur at all, or occurred only in a very limited degree, in the midwives' division. "Dr. Semmelweis now adopted the rule, that every one, before examin- ing a patient, should wash their hands with chlorine water. "When this rule was adopted, the patients on the physicians' side were not more frequently attacked by puerperal disease than those of the midwives. "In 1848, of 3780 cases delivered on the physicians' side 45 died, or 1'19 per cent. ; while on that of the midwives, of 3219 cases, 43 died, or 1*33 per cent. During the three years that washing with chlorine water has been used, the deaths on the two sides have been equal." (From a lecture by Professor Skoda, at the meeting of the Imperial Academy at Vienna, on the 18th of October, 1849, from which moreover it appears how small is the recognition which this great and practically important discovery has met with beyond the Academy. No doubt several causes of puerperal fever might be named, but no impartial person can doubt that this cause, discovered .in the Lying-in Hospital at Vienna, by Dr. Semmelweis, with all the acuteness of an unprejudiced philosopher, is one of them.) No. 5. THE FLESH OP ANIMALS TORTURED TO DEATH DANGEROUS AS FOOD. Page 251. "In order to procure a roast for Easter," says Dr. Reiser, "C iu R desired his family to set a snare for a roebuck. Accordingly, one of APPENDIX. 517 these poor animals was caught in the snare, which, as its head and breast had passed through, held it by the hinder part of the body, the abdomen and pelvis being inclosed in the cord, so that it must have succumbed after a most agonising struggle. It was found next day dead. ' ' The master and mistress of the family eat, on Easter day, the best part of this dainty ; the servants had little ; the remainder was laid in vinegar, but not eaten. "On the same day all in the family who had eaten of the venison observed a striking dryness of the mouth, oppression at the stomach, and nausea ; the features in all became anxious and pale ; all complained of oppression of the head, giddiness, and great weariness of the limbs. The master lost his sight for several days, and in short there now began a series of remarkable symptoms, requiring in many ways the assistance of Dr. Roser. The husband was only restored to health in July, but the wife never recovered ; she lingered more than two years, and at last died after severe sufferings. The daughter, the man-servant, and the maid, who had eaten little of the tortured animal, were soon cured. The symptoms in many respects recalled those of the effects of the bite of rabid animals (and of the sausage poison of Wirtemberg ?) " Dr. Roser concludes his communication in these words : "Many an animal (for example in hunt- ing) is tortured to death in the most barbarous manner, like the roe-deer in the snare. Ought not then the medical police to be led, by cases like this, to adopt the strictest regulations to prevent the use, as food, of animals which have been in any way tortured to death, and to insure that the animals intended for food are not tortured before being slaughtered?" (Dr. C. Gr. Carus. From the periodical "Der Menschenfreund in seinen beziehungen zur belebten Welt." A popular paper, published by the Dresden Society for the protection of Animals.) No. 6. LOCAL CAUSES OF INTERMITTENT FEVER. " The construction of the railway from Strasburg to Basle, rendered it necessary, at many points, to excavate the fields bordering the line to the depth of 1 to 2 metres (3| to 6g feet), to obtain earth for the mounds of dykes supporting the railway. This caused hollows extending to 13 or 14 hectares (32 to 35 acres) in size, and to a length of 3 kilometres (1| miles),, in the neighbourhood of the communes of Bollweiler and Feldkirch. In spring and autumn these hollows fill with water, which in summer par- tially dries up, and leaves a mud, very injurious to health. They have thus become true morasses, in which Herr A. Baumann found those plants which are peculiar to stagnant water, as Polygonum hydropiper, Arundo phragmites, Alisma plantago, &c., &c. " Under the influence of these dangerous swamps the commune of Boll- weiler, which has 1446 inhabitants, has been, for the last three years, most cruelly visited by intermittent fever. The following statement, confirmed by the Burgomaster, Herr Durwell, proves that the evil, instead of dimi- nishing, has become yearly greater. The following table gives the number of persons attacked with intermittents during the four years. "In the year 1843 36 ,, 1844 166 ,, 1845 743 , 1846 1166 518 APPENDIX. " The mortality has increased in the same proportion. The average mor- tality of ten years (1836 to 1845, including therefore some of the worst years of the intermittent fever,) is 36. In 1836 the deaths amounted to 54. In the same period, the days lost to the people in consequence of their inability to work, the fees of physicians, and the expense of medicines, amounted to 116,515 francs. "The little commune of Feldkirch, with only 480 inhabitants, suffered no less severely. The following is the account confirmed by the Burgomaster of the cases of intermittent fever in the four preceding years . " In the year 1843 2 1844 20 ,, ,, 1845 135 1846 376 ' ' The annual mortality rose from 1 1 to 1 8. The loss of work and the cost of illness amounted to 42,219 francs. To these facts Drs. Weber, Sanger, and West, the authors of a very decisive report to the Prefect of the Upper Rhine, add others, which are not less conclusive. The apothecary of Larger, in Soultz, the chief town of the three cantons affected by this plague, sold the following quantities of the sulphate of quinine : " In the year 1843 120 grammes. 1844 150 ,, 1845 970 "The state can no longer remain unconcerned and inactive in face of so gn.at an evil. Three years, full of suffering, have entirely prostrated the unfortunate inhabitants of Bollweiler and Feldkirch, and the writer of this letter, Dr. Dollfus-Ausset, turns to the Academy, that their knowledge may instruct the administration concerning the best means of checking the plague which has decimated two villages, and threatens others." (Comptes rendus de 1' Academic des Sciences a Paris, Seance du 5 Mar. 1847, p. 779. In the sitting of the 24th May, M. Sainte-Preuve proposed, as undoubtedly the best means of putting an end to this source of disease, to connect the hollows with running water, and thus cause the stagnant water to circulate. ) No. 7. REPORTED CASE OF SPONTANEOUS COMBUSTION. LETTER XXIV. Page 296. In order to judge of the degree of credit to be attached to historical facts, in the departments of medicine and the natural sciences, taken from newspaper articles, I will give the following example. In the Journal des Tnbunaux, and later in the Journal des Debatsof 24th February, 1850, the following article appeared : ' ' A most extraordinary circumstance has occurred in a tavern of the Barriere de 1' Etoile at Paris. Xavier Gr., a journeyman painter, whose habits of intemperance had acquired for him the nickname of Pochard, wagered, whilst drinking with his companions, that he would eat a lighted candle. He was challenged to do so, but had scarcely introduced the lighted candle into his mouth, when he gave a feeble cry and sank down, to the utter astonishment of the bystanders. A bluish flame was seen to play about his lips. In endeavouring to assist him, his companions wished to raise him, but were seized with terror on observing that the unfortunate man was burning internally. Scarcely half an hour elapsed before his head and the upper part of his chest were carbonised. Two medical men were APPENDIX. 519 called in, and recognised that Xavier had fallen a victim to spontaneous combustion, a positive phenomenon, but which science has not as yet been able to explain. This combustion of the human body is frightful in its intensity and rapidity. The bones, skin, muscles, are devoured, consumed, and reduced to ashes. A small quantity of dust on the spot where the victim has fallen is ail that remains of the body. "Although rare, these frightful accidents nevertheless occur, and the press has already had occasion to register cases of spontaneous combustion. We will only mention one instance, which occurred a few years ago, in a woman who was addicted to the immoderate use of ardent spirits. All the phenomena which characterise combustion were produced with energy ; the greatest por- tion of the body was entirely reduced to the state of a cinder, without the apartment in which this intense combustion had taken place exhibiting the slightest traces of fire. The woman had been first seized by the flames in front of the chimney, and in all probability at the moment she was attempt- ing to kindle some sticks by blowing on them. No mark of burning was seen on any of the furniture which surrounded her, nor on a chair against which she must have fallen. ' ' The fact of spontaneous combustion was known in the middle ages and in the following centuries, but being classified with miraculous facts, it had given rise to no positive or scientific observation ; so that in 1705 it was, in France, the cause of a man's being accused of the capital offence of having murdered his wife and attempted to burn her. " The accusation was not stopped by the physical impossibility of destroy- ing by fire a human body, without leaving any traces of burning in the chamber. Generally death by apoplexy immediately follows the attack of spontaneous combustion. Sometimes, however, the victim dies by slow combustion. In the Annales de la Medecine the case of a man is given, who died after burning for four days." In its form this article completely resembles those details, which make up the chief part of the Chapter on Spontaneous Combustion in the hand- books of forensic medicine, and of the articles on the same subject in medical dictionaries. As a fact of the most recent date, the article of the Debats must appear so much the more deserving of credit, as living witnesses are mentioned, and among them two physicians ; and further, no Parisian journal had contradicted the statement. I was, therefore, induced to investigate the source of the occurrence, and have obtained the most exact information from Mons. Regnault (Member of the Academy of Sciences, and one of the most distinguished natural philosophers of Europe) ; from Mons. Pelouze (Director of the Mint, and a celebrated chemist) ; and finally from Mons. Carlier, Prefect of Police. From the following letters it will be seen that this case of spontaneous combustion was simply a falsehood. "To Baron J. Liebig, Professor of Chemistry in Giessen, Corresponding Member of the Institute of France. I. "Paris, 12th March, 1850. "Mr DEAR LIEBIG, "On receipt of your letter I lost no time in seeking information about the famous cases of spontaneous combustion so much spoken about, but of which no one, not even among medical men, whom the subject more directly interests, has ever seen a single instance. Unfortunately I have had but little time at my disposal, as I am at this moment juryman at the Court of Assizes, and must consequently pass the whole day in the Court. 520 APPENDIX. "I need scarcely tell you, that I do not in the slightest degree believe in this extraordinary phenomenon. To admit the physical impossibility of the fact it is sufficient to reflect an instant on the difficulty of the combus- tion of the matters which form the human body ; on the immense quantity of water which must be evaporated before the calcination and the combus- tion of these substances can commence ; on the absence of oxygen in the cavities of the interior, the small quantity of this gas found in them being very soon consumed, and the combustion of the alcohol or of the other volatile combustible matters being arrested by that circumstance itself. " On this point I have consulted those among our medical men who have been for many years the most distinguished, and particularly Mons. Ma- gendie, but not one is acquainted with a circumstance of this nature. This is not due to the want of announcement of facts of this kind in the public journals ; but whenever trouble has been taken by competent persons to go to the source of the report, the marvellous has always disappeared with the fact itself of the combustion. "As to the story of the Barriere de 1' Etoile, I have no doubt that it is a puff, if it has not been invented with a criminal intention. If I had had time, I would have made inquiries at the Commissioner of Police of the quarter, and at the Prefecture of Police. But I have heard that Mons. Pelouze has already obtained all the information, which he will immediately transmit to you. "V. REGNAULT." II. " Paris, March 9th, 1850. "My DEAR FRIEND, The result of all the information which I have been able to collect from different sources as to the facts related in the Journal des Debats of 24th February, 1850, is that it is a pure fabrication. Among the exam- ples of spontaneous combustion, it would certainly have stood as the most extraordinary, not to say the most incredible. Knowing very well the article in which this ridiculous story was related, I never looked upon it in a serious light. However, as you attached some importance to the state- ment, I made inquiries, and have satisfied myself that it is a total false- hood. " I am not aware that a single medical man believed in the story for a moment, &c. "PELOUZE." III. PREFECTURE OF POLICE, FRENCH REPUBLIC, 1. Division, Liberty, Equality, Fraternity. 1. Bureau. 2. Sect. PARIS, 7th March, 1850. " SIR, " I am in receipt of the letter which you did me the honour to write on the 4th of this month, in which (in consequence of a criminal process pending before the Assizes of Darmstadt) you make inquiries about a case of spontaneous combustion, which, according to an article of the Journal des Debats, occurred lately in Paris. "The fact is entirely imaginary. If the statement of the journal had been correct, the accidental death of the pretended Xavier Gr. would have led to legal investigations, the knowledge of which must necessarily have come under my administration ; but the most careful researches on this point in my bureau have been without any results. "Wishing, nevertheless, to remount to the source of the fact related in APPENDIX. 521 the Journal des Debats, I have learned that the article inserted in this journal was borrowed from the Gazette des Tribunaux. On making inquiries at the office of this journal, it was not difficult to gather from the manner in which the questions were received, that the story was a fable invented for amusement. " The Prefect of Police, "P. CARLIER." No. 8. RECENT ESTIMATION BY BISOHOFF OF THE QUANTITY OF BLOOD IN THE HUMAN BODY. NOTE TO LETTER XXVI. Page 339. In a memoir recently published in the " Zeitschr. f. wissensch Zoologie," Bd. ix., Bischoff confirms his former estimate (made by Welker's colour method) of the quantity of blood in the human body. The criminal on whom he operated was a perfectly healthy man, 26 years of age, whose body he had an opportunity of weighing before execution. He also sub- mitted Welker's method to a series of trials to test its accuracy. Grammes. Ibs. avoir. The blood collected after decapitation . .3510 772 Blood remaining in the body after decapitation and extracted by water . . . . 1348 2 '96 Total weight of blood in the body ' i . 4858 10 '68 Weight of the naked body before execution 68010 grammes=:149 > 6 Ibs. avoird. Eng. The quantity of blood is therefore ^ of the weight of the body, which corresponds nearly to his former estimate of J. In a third case, in which he unfortunately could not procure a specimen of the blood, in order to estimate the total amount in the body, he ascertained that by decapitation, the same quantity was lost as in the previous instance. He concludes from his experiments that by decapitation, a man weighing from 135 to 145 Ibs. Eng. loses 7^ to 8 Ibs. of blood, and about 2| Ibs. remain in the body. He has not had an opportunity of estimating by this method, the quantity of blood in a female. Wrisberg states that he col- lected 26 Ibs. from a beheaded woman. J. B. No. 9. FOOD CONSUMED BY WORKING MINERS AT THE ELEVATED MINES OF GASTEIN AND KAURIS. LETTER XXVI. Page 338. I regard as sufficiently important to be added, in form of a supplement to this letter, a number of determinations of the food of working-men, made willingly at my request, and with great care, by Mine Director Reis- sacher in Bockstein. These determinations refer to the consumption of dif- ferent kinds of food by the gold miners in Rauris, Bockstein, and Kristof. Bockstein lies at the end of the valley of Gastein (47 4' N. Lat. and 13 4' E. Long.). The work of the miners consists chiefly in boring and blasting the auriferous rocks of quartz, schistoze and quartzose gneiss. In the high Goldberg in Rauris, the miners work at an elevation of 75 UO Vienna feet * above the surface of the sea ; at the Rathhaus mine, near Bockstein, the mining house of Hieronymus is situated at an elevation of 6064 feet ; and that of Kristof at 6700 feet. Rauris. The observations extended over a * Vienna foot = 12'445 inches English. 522 APPENDIX. period of four weeks ; from 27th Oct. to 28th Nov. 1857. In each week the miners worked four days ; and their sojourn at the mine extended from Monday evening at 6 o'clock, to Friday at 1 ; in all 91 hours. During this time 6 men received 12 meals. They were strong full-grown men, from 35 to 45 years of age, and their chief work consisted in boring the rock. The whole period of sojourn of the six men at the mine amounted to 2184 hours ; of which 1200 were devoted to work, and 984 to eating, rest and sleep. The miners required eight hours to ascend the mountain from their place of residence to the mine ; each man carried his own supply of fat and flour for two weeks, and the other necessaries for one week. The 6 men consumed in the given period of 2184 hours of their sojourn on the high Goldberg, the following quantities : Beef suet 40 Ibs.* Wheaten flour 144 Salted goat and sheep's flesh .... 64 Rye bread . . . . . . . . 52J Beans 2 Barley 20 White cheese (made of sour milk) . . . 4^ Fat cheese 1 Common salt .3 Beer 64 Ardent spirits . . . . . 2maas. * Water 397 Ibs. There were in all 2804 inches of boring made and exploded by the 6 men. The bore was 15 Vienna lines* in diameter; the hammer weighed 3 Ibs., and each blow communicated to the borer a velocity of 21 feet per second.. In a second, the men made 40 blows, and bored on an average in pure quartz 1 inch, in quartzose gneiss 1 '3 inch, in schistose gneiss 1 '1 inch, per hour. (a) Bockstein. By Hieronymus. Duration of the experiment, 3 weeks,from 31st August to 18th September inclusive, 1857. Number of workmen, 27. Period of labour, 4131 hours: cooking, rest, and sleep, 2808. Total number of hours spent at the mine, 6939. There were consumed Beef suet 83 Ibs. Wheaten flour 234 Rye bread 233 ,, Salted goats' flesh 55| ,, White cheese . . .*' '-*- . . . . 6 ,, 61 2 J Ibs. Goats' milk t . . . . ' . . 1012 '5 Ibs. Eggs (number of) 6 (b) By Kristoff. Duration of the observations, 4 weeks, from the 5th * The Austrian pound = 1-235 Ib. English. The Maas = 0-3114 imperial gallon. The Vienna line = 0'0864 inch. English, t Goat's milk contains Water = S7'l Composition of the solid matters. / Butter = 5 '10 Solid matters = 12 9= ) Caseine = 3 "60 ) Milk sugar =2 -951 lOO'O I Salts =1-249 12-900 APPENDIX. 523 to the 30th of July inclusive. Number of workmen, 15. Hours at work, 3378; cooking, rest, and sleep, 2442 : together 5820 hours. There were consumed Beef suet 66 Ibs. Wheaten flour 206 ,, Rye bread 190^ ,, Common salt 2 ,, 464 1 Ibs. Goats' milk, 1515 Ibs. (905 Vienna maas = 281 '8 Imp. gal. Eng.) Comparison. Each man consumed when working hard at a height of 6000 to 7000 feet above the level of the sea Bockstein. Kauris. Kristof. Hieronymus. Goldberg. Beef suet .... 0'273 0'287 0'439 Wheaten flour .... 0'849 0'810 1'582 Rye bread . . . . 0'785 0'806 0'577 Flesh 0-192 0703 Beans 0'263 Barley 0-219 White soft cheese . . . 0'210 0'049 Cheese O'Oll Common salt .... O'OOS 0'033 Pounds of solid food . . 1-915 2'305 3-876 Goats' milk* (Ibs.) . . . 6'246 3-501 Beer (maas) 0'252 Ardent spirits (maas) . . 0'024 Water (Ibs.) . . . . 4'812 It would be out of place here to enter upon all the inferences which might be drawn from these numbers. One fact is, however, brought pro- minently out ; viz., that the consumption of carbon by a hard-working adult at a height of 6000 to 7000 feet above the level of the sea, is not smaller, but rather greater, than in the case of a soldier in Darmstadt. On Goldberg by Rauris, a man consumed daily 2170 grammes (4'81b. Eng.) of solid food, of which 243 grammes (8oz. Eng.) were fat. If the per- centage of carbon in the solid food be reckoned at 40, then it will contain 868 grammes (30? oz. Eng.) of carbon, which is rather below than above the mark. The carbon of the beer and ardent spirits is not taken into the calculation. In the above experiments, the complete replacement of flesh by milk is remarkable. The miners at Kristof, during the time of labour, partake neither of flesh nor ardent spirits, and perhaps many would see a certain connection between these two as with tobacco. It is certain that the work performed by the flesh and beer consuming miners in Rauris is not greater than that of the Bockstein miners, who used milk and farinaceous diet ; and we may conclude without risk of error, that no necessary relation exists between hard labour and the consumption of ardent spirits and flesh. * Containing Butter = 0-318 Milk sugar = 0'183 Caseine = G-2'24 Salts =0078 Solid matters = 0'803 524 APPENDIX. In the above proportions, milk and bread produced in the human body the same amount of working power. At the conclusion of his report, Herr Mine Director Eeissacher makes some remarks, which might, perhaps, interest many. I give them in his own words : ' ' Although, on an average, there is but little difference in both mining districts in the work and the amount of strength for the purpose required in people of the same age, yet, from the severity of its climate, the sojourn is much more trying for the miners at Kauris, in the midst of the glacier regions, than at Eathhausberg, where there are no glaciers. In Kauris, on the high Goldberg, the glacier extends 1| mile downwards from the mining house, and communicates to the neighbourhood all the peculiarities of the glacier regions. Apart from the greater distance of their dwellings, the journey to the mine in Eauris is, on account of the glacier and its storms, much more laborious to the miners, than it is to Gastein ; and fatal accidents from cold occur not unfrequently in Eauris, but never in Gastein. "The expenditure of strength in the ascent of the mountain is in Gastein, as well as in Eauris, greater than is required for the work of the mine, and in proportion to the inhospitality of the climate in Eauris, so is the ability to labour in the Eauris miner of shorter duration than in Eathhausberg. In Eauris, none but a thoroughly healthy and powerful man can bear the ascent of the mountain ; hence it happens that, including the young, each fourth man belongs to the military grade, or has served as a soldier. In spite, however, of this bodily vigour, it is observed as a rule, that at the age of 40, and after a service of 20 years, the Eauris miner can no longer bear the mountain ascent, though he may still be capable of working at Gastein. " On the other hand, it is found at Gastein, that at the age of 50, and after a service of 30 years, the miner is unfit for further work, and chiefly because he is no longer able to climb the mountain. ' ' Difficulty of breathing, and loss of power in the legs, compel them to quit the Alpine regions. ' ' This difficulty of breathing, with premature old age, is not caused by the damp air of the mines, nor by the smoke of the powder, nor the dusty air of the crushing rooms. These may assist ; but the chief causes lie in the ascent of the mountains by the miners with their burdens, and by their sojourn in the Alpine and glacier regions. The proof of this state- ment is found in the fact, that inspectors and day-labourers, who are not subjected to the first sources of danger, become, in like manner, unfit for service. "Eepeated experiments have proved that dogs, and cats especially, cannot live on the Goldberg at Eauris ; the latter dying, even when in pairs, after 4 to 6 weeks. Just as with man, but in a much shorter time and in a more striking degree, there occurred in the case of these animals difficulty of breathing, and loss of power in the extremities, with dimi- nished appetite. "Even with men, all these effects take place in a shorter time, if the residence on the mountain has been continuous, and hence we can easily understand why the miner feels the necessity of the weekly descent from the mountain, in spite of the length of the joxirney to and fro and of the stormy weather ; because he thereby preserves his health, appetite, and strength, notwithstanding the difficulties of the road. "K. EEISSACHER. , llth August, 1858." APPENDIX. 525 No. 10. A NEW SOUP FOR INVALIDS LETTER XXXII. Page 433. Take half a pound of newly killed beef or fowl, chop it fine, add 1 Ib. of distilled water, with four drops of pure muriatic acid, and 34 to 67 grains of common salt, and stir well together. After an hour the whole is to be thrown on a conical hair sieve and the fluid allowed to flow through with- out any pressure. The first thick portions which pass through are to be returned to the sieve, until the fluid runs off quite clear. Half a pound of distilled water is to be poured in small portions at a time on the flesh residue in the sieve. There will be obtained in this way about a pound of fluid (cold extract of flesh), of a red colour, and having a pleasant taste of soup. The invalid is allowed to take it cold, a cupful at a time at plea- sure. It must not be heated, as it becomes muddy by heat, and deposits a thick coagulum of albumen and colouring matter of blood. The illness in my house of a young girl, 18 years old, of typhus, was the occasion of this preparation being first made ; and my attention was directed to it by the remark of my family physician (Dr. Pfeufer), that, in a certain stage of this disease, the greatest difficulty that the medical man had to contend with, lay in the defective powers of digestion, consequent on the state of the bowels, and likewise in the want of such food as would be capable of undergoing digestion and forming blood. In soup prepared in the usual way by boiling, all those constituents of flesh are wanting which are necessary for the formation of blood albumen ; and the yolk of egg which is added, is poor in those substances, for it contains in all 82^ per cent, of water and fat, and only 17^ per cent, of a substance the same or very similar to albumen of egg. But whether it is equal in its powers of nutri- tion to the albumen of flesh, is at least doubtful from the experiments of Mageudie. Besides the albumen of flesh, the new soup contains a certain quantity of colouring matter of blood, and with it a much larger quantity of the necessary iron for the formation of the blood corpuscles, and finally the muriatic acid to assist digestion. A great obstacle to the use of this soup in summer is its liability to change in warm weather. It enters into fermentation, like sugar with yeast, but without acquiring a bad odour. What may be the substance which gives rise to this fermentation, is a question well worthy of being investigated. The extraction of the flesh must consequently be made with very cold water, and in a cool place. Iced water, and external cooling with ice, completely remove this difficulty. But the most important point to be attended to, is to employ meat quite recently killed, and not several days old. This soup is made use of in the city hospital of Munich, and has already passed into the private practice of several of the most distinguished physicians of the city (Munich), such as Dr. V. Grietl and Dr. Pfeufer. I would perhaps have hesitated in giving more publicity than it deserved to so simple a circumstance, had I not been fully convinced of the great power of nutrition of this soup from a recent and particularly important case in my family. The wish naturally arose that its benefit should be extended to a larger circle of sufferers. A young married lady, who was not able to take any solid food in consequence of an inflammation of the ovary, was supported for two months, until her health was completely restored, by the sole use of this soup. During this time she visibly improved in flesh and strength. As a rule, patients take this soup without opposition, only so long as they are ill ; but they have a distaste for it as soon as they are able 526 APPENDIX. to eat other food. This may perhaps be due to the colour and faint smell of flesh which it possesses. On this account it may therefore be of use to some to colour the soup, with burnt sugar, and to add to it a glass of the best claret. No. 11. A METHOD FOR IMPROVING THE QUALITY OP BREAD. It is well known that the gluten of cereals undergoes a change when moist. When fresh it is soft, elastic, and insoluble with water, but it loses these properties by long contact with water. If kept under water for some days its volume gradually diminishes, and it is finally converted into a slimy muddy fluid, which will no longer form dough with starch. The property of flour to form dough is essentially dependent on the power of the gluten to unite with water and to transform it into the state, in which, for example, it exists in animal membranes, in flesh, and in coagulated white of egg. Dry substances are not moistened by the water present in these. By keeping flour in store, the gluten of the cereals undergoes a change similar to that occurring in the wet state, in consequence of this highly hygroscopic substance attracting moisture from the air. The flour gradually loses its property of forming dough, and the quality of the bread also deteriorates. It is only by artificial drying and exclusion of the air that this deterioration can be prevented. With rye flour this change takes place as rapidly, and perhaps still more so, than with wheaten flour. About 24 years ago (see Kuhlmann, Pogg. Ann. der Phys. u. Chem. bd. xxi. s. 447) the Belgian bakers employed means for communicating the quality of the freshest and best flour to damaged flour, which by itself would only have furnished a heavy and moist bread. These means con- sisted in the addition of sulphate of copper or alum to the flour. The action of both substances in the preparation of bread depended on their forming by heat a chemical compound with the altered and soluble gluten, by which the latter recovered all its lost properties of insolubility, and its power to unite with water. The many properties possessed by the gluten of the cereals in common with caseine, induced me to make some experiments with the object of replacing these two deleterious compounds by some other harmless substance with similar action. This substance is pure, cold saturated lime-water. If the portion of flour destined for the dough be made up with lime-water, and the leaven then added, and the whole left for some time, fermentation takes place just as if no lime-water had been used. On adding, at the proper time, the rest of the flour, to the fermented dough, forming the loaf and baking as usual, there is obtained a beautiful, solid, elastic, highly porous bread, free from acidity and moisture, of most excellent flavour, and which is preferred to all others by those who have eaten it for some time. The proportion of flour to lime-water is 19 to 5, that is, 100 Ibs. of flour require 26 to 27 Ibs. of lime-water. This quantity of lime-water is sufficient for the formation of the dough, common water must therefore be afterwai-ds added in the proper proportions. As the acidity of the bread disappears, the quantity of salt must be increased, to render it palatable. With regard to the quantity of lime in the bread, we know that 1 lb.' of lime is sufficient for the preparation of more than 600 Ibs. of lime- water ; if, therefore, the bread be made with the above proportions, the amount of lime will be nearly the same as in an equal weight of the leguminous seeds. APPENDIX. 527 It may be regarded as a physiological truth, ascertained by experience and experiment, that the full power of nutrition is not possessed by the flour of the cereals. From all that we know on the subject, it appears that the reason of it lies in the deficiency of the lime indispensable to the formation of bone. The seeds of the cereals contain sufficient phosphoric acid, but much less lime is present in them than in the leguminous plants. This circumstance may, perhaps, explain many diseases which are observed among children in the country, or in prisons, where the food consists chiefly of bread, and, on this account, this employment of lime-water merits the attention of physicians. The quantity of bread yielded by the flour is probably increased, in consequence of the greater attraction for water. From 19 Ibs. of flour without lime-water there were seldom obtained in my house more than 24^ Ibs. of bread ; but the same quantity of flour, with 5 Ibs. of lime- water gave 26 Ibs. 6 oz. to 26 Ibs. 10 oz. of good, well-baked bread. Now, as Heeren estimates the quantity of bread from the same amount of flour at 25 Ibs. 1 P 6 oz., it appears to me that the increase is undoubtedly due to the use of the lime-water. No. 12. To BAKE BREAD FROM THE FLOUR OP SPROUTED GRAIN. An important problem has been lately solved by Dr. Julius Lehmann, Chemist to the Experimental Agricultural Institution of Weiblitz by Bautzen, viz., the preparation of bread from the flour of sprouted rye. The Ministry of the Interior of Saxony commissioned Dr. Lehmann to investigate, chemically, several points connected with the most important articles of food, and his attention was particularly directed to the above problem. The experiments instituted by him on this point established, that the changes produced in the grain of the cereals by germination consist chiefly in the partial solubility of the gluten, and the consequent loss of its elasticity and ductility (the properties necessary for the formation of dough). It was further ascertained, that the partially soluble starch is transformed, by means of the small quantity of diastase from the gluten, into dextrine and sugar. Further experiments led to the fact, that common salt possesses the property of rendering insoluble the dissolved gluten, and of again communicating to it its quality for forming dough. Continuous rain during the rye harvest having caused the sprouting of a large quantity of grain, experiments based on the above observations were first made in the bakery of Herr Ochernal at Techritz, and as favourable results were obtained, they were followed up by Dr. Lehmann, with permission of the Ministry of the Interior, in the military baking establishment at Dresden, under the superintendence of Military Com- missioner Blume. For these experiments rye was selected completely sprouted ; it was ground with all the sprouts. One scheffel, * weighing 160 Ibs.* gave the following quantities : Good flour 102 Ibs. Seconds . 17 Thirds 15 Bran 18 Loss '"' 9 Forty pounds of the good flour were mixed in the usual way w th 31 Ibs. of water, and the necessary quantity of leaven, and the experimental * In Saxony the Scheffel = 2 "86 English bushels : the pound = 103 Ibs. English. 528 APPENDIX. loaves weighed from this mass. It was found that the bread baked without the addition of anything, spread out into a flat cake-like shape, its crust separated, bluish dough- spots formed on it, and it was unfit for food. By the addition of 300 grains of salt to 3 Ib. of flour, the bread was materially improved. It retained its form, the crust still separated, and a slight bluish dough still showed itself on the under side. The bread was, however, eatable. The addition of 1 oz. of salt to 3 Ibs. of flour produced the full effect. The bread was in every respect good ; it was porous, dry, well -flavoured, and without the bluish dough-spots.* The manipulation is very simple. The salt, dissolved in water, is added before kneading ; in other respects the procedure is the same as usual. Experiments made with flour from sprouted wheat have as yet led to no favourable results. They are to be continued. Besides the property which, we have seen from the above, is possessed by salt, of enabling us to use sprouted with as much advantage as unsprouted corn in the preparation of bread, it has still others which are highly deserving of notice in bread-making. Independently of the necessity of salt to promote the complete digestion of the proteine substances in bread, its presence is valuable for the prevention of mould. The experiments of Dr. Lehmann have proved, that no mould formed, even after months, on bread baked with salt, whereas when it was not added, the mould made its appearance even after a few days. Finally, the addition of salt produces a much whiter bread. This fact has been proved not only by the experiments of Dr. Lehmann, made two years ago, but Mege-Mouries has also lately directed attention publicly to the circumstance. Apart from the peculiar importance of the addition of salt to flour from sprouted rye, for the purpose of baking, it would be highly desirable, in the event of our public attaching itself to the custom, already generally introduced into the south of Germany, of eating salted bread, that the butter used with it should not be salted, unless it is intended to be kept in store for a length of time. For, besides the general good dietetic effects of such a custom, we should not, in years in which the grain is much sprouted, have to overcome the peculiar difficulty of accustoming the con- sumers to the use of salted bread. The secondary effect of the reforming of abuses connected with the sale of salted butter would also not be unimportant. These propositions should be well considered by all those who are interested in the important question of the supply of food. But the question in the first place is, to provide for the rapid and general introduction of the baking of flour from sprouted rye by the addi- tion of common salt. No. 13. LEGENDS OF THE EHINEGAU. Page 470. " The voice of the people has embodied in a merry tale the genial dis- position of the jovial Rhinelauder. Nowhere," so runs the story, "do men so rarely lay violent hands on themselves as on the banks of the * I have myself seen this bread, and found it to possess excellent qualities. J. L. APPENDIX. 529 Rhine. It is especially an unheard-of event in the chi'onicles of that valley, that a man, tired of life, ever selected the mode of suicide by hanging, which is characteristic of the gloomiest melancholy. There was only one man in the Rhine valley who ever wished to hang himself. All his goods and gear were gone, he had pledged the last of his furniture for debt, and his creditors had left nothing but half a cask of wine in the cellar. Then the man went to the garret, took a new rope, rubbed it with oil, that it might run smoothly, twisted a most artistical noose, and placed himself under a cross-beam. But, as he was on the point of taking the eventful journey, the half cask of wine in the cellar came into his mind. Only one draught to help him on the road ! He considered long ; but he stole down, took the spigot, and inserted it at the bung-hole, where the best liquor, the noblest heart's blood of the cask, is always found, and drew a single pint. And when he had drained that, he found that the wine was good, and took a second. At the third measm-e he thought how foolish it would be to leave so large a legacy of the good wine to his laugh- ing heirs ; so he turned down a fourth. But when he had reached the seventh pint he gently raised the bung, took the new, oiled rope, threw it into the cask, and cried, ' Drown thyself, cursed rope ! I will first drain the cask to the dregs, and then we shall see what is to be made of thee.' But when the man, some time after, had drxink out the cask, he found that the rope was no longer fit for use. That was the only man of the Rhine who ever wished to hang himself. "For the last thousand years the life of the Rhinelander is, as it were, steeped in wine ; he has become, like good old wine casks, tinted with the vinous green. This gives him his originality. For there are many wine countries in Germany, but none where, as in the Rhinegau, wine is every- thing. Wine is the creed of the Rhinelander in everything. As in Eng- land, in the days of Cromwell, the royalists were known by their meat pasties, the papists by their raisin soup, the atheists by their roast beef, so is the man of the Rhinegau known, time immemorial, by his wine-flask. "In the Rhinegau they tell of mothers who gave their new-born children, as their first" nourishment, a spoonful of good old wine, as if to impress on them in the cradle the stamp of their native home. A valiant 'Brenner' (burner), as on the Rhine they call the thorough jolly com- panion, drinks every day his seven bottles of wine, and with it grows as old as Methuselah, is seldom drunk, and has at most the Bardolph mark of a red nose. The characteristic heads of the seasoned winebibbers, of the hair-splitting connoisseurs in wine, who, however, are one and all unable, with bandaged eyes, to tell red from white by taste alone ; of the prophets, of the sample- hunters, the men who travel from one sale of wine to another, and drink their fill, gratis, of the samples ; are nowhere to be seen in an originality so fresh as in the Rhinegau. All these physiognomies, in their infinite varieties, when collected as a wine-tasting group, appear like the sailors' taverns among the old Dutch, likely to become a standing theme for our modern painters of character. "The chronology of the natives of the Rhinegau is not calculated on calendar years, but on wine years. Unfortunately their usual reckoning, from one distinguished vintage to another, agrees pretty nearly with the Greek system of Olympiads. The whole speech of the Rhinelander is embroidered with original expressions, which point to the culture of the vine. They would fill a lexicon. Several of the customary words of praise applied to wine, are a poem from the people's lips, condensed into one word. Thus it is prettily said of a right noble liquor 530 APPENDIX. of the last year, 'There is music in that wine.' A good old wine is a 'Chrysam,' a consecrated oil. The 'flower' (Blume) and 'bouquet' of wine have already become, from local expression, terms universally employed. The Rhinelander is as rich in such splendid poetical names for his wine as the Arab is in poetical epithets for his noble steed. In the middle ages the inferior, sour wine, ' the quart whereof was scarce three farthings worth,' was called on the Rhine 'Councillor;' but hardly for the innocent reason given by a late chancellor, when he says, ' for, how- ever much of it one might drink, it left a man his full understanding, as all councillors should be men of understanding.' Poetically figurative is the modern name of ' Dreimannerverein ' (association of three men), given in the Rhinegau to a wine which can only be drunk thus : two men hold the drinker fast, while the third pours the noble liquor down his throat. As expressive, musically, sounds the grumbling word 'Rambass,' for a rough, coarse, tasteless, blunderer among wines. The ' Groschenburger," (penny wine) of the Rhinegau, corresponds to the 'Batzenwein' (also penny wine) of Upper Germany. " The Rhinegau has even its own 'wine saints.' First, St. Goar, whose cask, a gift from the Emperor Charlemagne, always filled itself, and who loaded with gifts his guests, provided they had previously undergone baptism with water, and desired also from him the baptism of wine. The legend of St. Theonest, the patron saint of Caub, who went through the trials of martyrdom by floating down the river through the whole Rhinegau in a leaky wine-barrel, and at length landed alive at Caub, where he planted the first vines, also contains one of the plainest and most intelligible symbolisations of all the sufferings or tortures which the grape has to undergo before, rising from the bands of death in the fer- menting- tub, it is glorified or transfigured into the golden wine. "When the North German porter groans under a heavy burden, and is compelled, in order to advance at all, to set it down at short intervals, he strengthens himself for each new effort by a hearty curse, which never fails to help him. But when the Rhenish coopers have to carry up out of the cellar a heavy cask, which they must take up again after every pause, they strengthen themselves for each new attempt by a hearty draught of wine, and this, too, never fails. Not less inexhaustible than the poetry of the vineyard, but as yet little studied, is the poetry of the wine-vault or cellar. Not alone have the castle of Johannisberg and the convent of Eberbach their wines stored in splendid vaults, where the double gleam of the broken daylight and the glimmer of lamps is so majestically reflected from the vaulted roof, while heavy buttresses cast their gigantic shadows between ; the same is seen, on a smaller scale, in hundreds of old private cellars, magnificent subterraneous buildings of their kind. When in early winter the cellars are filled with the stupefy- ing vapours of the fermenting new wine, then, when it is necessary to descend, firebrands are pushed down from one flight of the cellar stairs to another, and while through the dark depths the hai*sh lights flash, men can go down gradually to the casks under the protection of the purifying flame. When in spring the Rhine flood unexpectedly rises into the well- stored cellars, the coopers often sail about them in wine tubs, like St. Theonest, to fix the casks to the ground, in order that they may not' be carried away. But they cannot always keep above water so skilfully as the saint, and this causes the most laughable adventures." (Supplement to the Augsburg A llgemeine Zeitung : 18th November, 1850.) INDEX. ACIDS Acidification checked Adhesion . . Affinit PAGE 99 . 240 .134 87 Agriculture, an art and a science 493 mechanical opera- tions of . . 497 - rational principles of. . . . 487 Air, composition of expired . 357 vitiated by respiration . 363 Albumen, its importance . . 370 of blood, its compo- sition . . . 454 relations of, to fibrine, caseine, &c. . .457 Alchemists . . . .50 elements of . . 75 Alchemy, its true nature . 54 Alcohol ..... 213 as a respiratory mate- rial . . . .470 Alcoholic fermentation . . 257 Alkalies, effect of, on the blood 419 Allotropic state . . . 182 Alum, effect of, on bread. . . 459 Alumina soluble . . .515 Amorphous forms . . .179 Amygdaline, fermentation of . 221 Analysis ..... 8 Animal heat . . . . 345 Animalcules .... 259 Annual plants, their food . 490 Anti-phlogistic theory . . 59 Applied Chemistry . . 11 Arabians, their learning . . 41 Archseus of Paracelsus . . 83 Ardent spirits, effects of . . 471 Aristotelian philosophy . .69 Ashes of food and blood . . 406 PAGE Ashes of food, soluble and inso- luble 415 Atomic motion, communicable 231 theory . . . 104 volumes . . . 123 weights . . .108 Atoms, physical and chemical . 105 compound . . . 107 forms of .. . . Ill Attraction, direction of . 198 B. . 125 . 99 . 78 . 243 . 158 . 274 BALANCE, the Bases Basil Valentine . Bavarian beer . Beet-root sugar . Bile Bischoff's views . . . . 28g estimation of quan- tity of blood in man . . . 521 Bitter almonds, oil of, as an ozoniser . 187 hydrocyanic acid from . . 220 Bleaching . . . .235 powder . . . 145 Blood, absorption of oxygen by 358 action of alkalies in the 419 alkaline state of . .407 carbonates and phosphates in 413 composition of. . .369 altered by food 413, 422 effect of organic acids on 421 constituents in vege- tables . . .375 iron of . . 449 INDEX. PAGE Blood, of man and carnivora . 422 quantity of, in man 339, 521 salts of . . . 405, 425 Body, changes in . 505 forces in operation in . 277 Boiling points .... 324 Boutigny's experiments . .132 Bran, nutritive value of . . 464 of wheat, composition of 465 Bread, adulterations of . . 459 making, theory of 223, 4(50 means of im- proving . 526 from flour of sprouted grain 527 c. CANE SUGAR . . . .382 Carbon, daily consumption of 340 of plants, its origin . 202 Carbonic acid, solid and liquid 130 its danger 133 amount of, in respiration . 341 not formed at the lungs . .361 the cause of dis- ease . . . 365 Carlier, letter of, on spontane- ous combustion . . . 520 Carnivora, nutrition of . . 373 Caseine . . . . .372 composition of . . .454 Cavendish .... 53 Cheese, preparation of . . 226 ashes of ... 450 Chemical affinity ... 87 analysis ... 8 attraction modified . 196 combination . . 86 compound . . 87 decomposition . .87 equivalents . 93 formulae . . .335 implements . . 124 theory . . .11 transformations. . 333 and vital force . . 19 Chemistry a language . . 9 origin of 5, 37 _ utility of . 21, 31 Chimpanzee, similarity to man 288 PAGE Chocolate, action of . .471 Choleic acid . . . 454 Cholicacid . . . .452 Chondrine . . . . 452 composition of .455 Circulation of the blood . . 354 Clay, effects of burning on . 501 Cod salted, ashes of . . .451 effect of lime water on 451 Coffee, action of . . 471, 475 Cohesion, influence of . .91 Cohesive attraction . . . 91 Columbus . . . .65 Combining proportions . ' . 97 Composition and boiling points 325 Conservatoire des Arts, Mu- seum of, repaired . . 170 Contagion, propagation of .251 Copernicus . . . . . 66 Cork 124 Coupled*compounds . . . 205 Crum's soluble alumina . . 515 Crystalline form . . . 179 D. DARK AGES, teaching of . .63 Decay 233 Definite proportions . . 95 cause of .103 Development theory . . 287 Diastase 229 Diet, effect of . . . .467 Dietetics 14 Digestion . . . .228 checked by coffee . . 475 Dissection wounds . . . 250 Dough, how formed . . . 224 Drought, effect of . . .491 E. ELECTRICITY as moving power, 154, 171 and steam compared 155 Electro-magnetism . . . 157 Elements of alchemists . . 75 Engravings copied by chemistry "280 Equivalents . . . . ! and atoms . Ereinacausis transferred. 109 233 237 INDEX. 533 PAGE Excrements of animals . .506 composition of 509 vary with food 509 F. FALLOW . effects of Fat, formation of use of . i Fermentation . 499 495 399 397 201 (influence of heat on . . 213, 246 theories of . 230, 253 Ferments . . .. 215, 218 Fibrine 371 composition of . . . 454 Flesh, composition of . . 435 juice of . . . 437 infusion of . . .435 Flour changed in bread-making 223 substitutes for . . . 462 unbolted . . . .465 Food and labour . . . 391 fermentescible . . . 249 mineral constituents of . 405 same as in blood . 406 plastic and respiratory matter of . . 385 and respiration . . . 341 salts of, in urine and faeces 414 Forces, Mayer's views of . .167 Fuchs' water-glass . . . 147 Fungi, action of ... 263 in fermentation . . 257 Fusel oil 217 G. GALEN'S system of medicine . 72 overthrow of . 81 Galileo . . . . 68 Gas, from wood . . .163 condensation of . . .135 liquifaction and solidifica- tion of . . . . 130 Geber's writings . . . . 43 Gelatine not nutritious . .443 Gelatinous tissue, composition of 455 PAGE German agriculture . . . 393 Germination, effect of . . 224 Giessen, experiment with mineral manure . . .510 Glass, composition of . .146 soluble . . . 147 Gluten, nutritious value of . 463 action on starch of .224 ashes of . . .463 Glycocoll 452 Gold, growth of . . . 48, 74 Golden tooth, boy with . .515 Graminivora, nutrition of . . 373 Guttenberg . . . .67 H. HEAT, influence of . . .89 modifying effects of . .196 produced in combustion. 367 Houses, moisture in new, re- moved by carbonic acid . 365 Hydrochloric acid, action of, on food . ... 427 I. INDUCTIVE PHILOSOPHY . . 23 Infusoria, action of. . 261, 263 Innocents, cemetery of . . 236 Inosinic acid . . . . 439 Inosite 439 Iron, importance of, in blood . 450 Isomerism 176 Isomorphism . . . .116 K. KKEATINE Kreatinine LAVOISIER Leaves, decay of Leblanc . Leidenfrost's experiment Life . 437 . 437 37 491 142 132 299 Lime, effects of, in agriculture 491 534 INDEX. PAGE Lime, chloride of . . . 145 water, in bread-making. 459 Luther ..... 67 M. MACHINES create no power . .165 Manures ..... 504 Mariotte,law of . . .129 Materialists, views of . . 293 Mathematics, uses of . . . 7 Matter, states of . . . . 129 Mayer's views of forces . .167 Meat, proper mode of boiling . 437 roasting . 438 ashes of fresh . . .446 exhausted . .446 exhausted by boiling \ ^^. not nutritious . J extract of, valuable . 441 preservation of . . 247 salted, loss of nutritive value in . . . 447 Medical theories . . .83 Medicine, the universal . . 78 Metals ..... 87 transmutation of . . 43 Metalloids .... 87 Milk, elements of. . . . 372 sugar . . . .381 Mineral food for annuals . . 490 perennials . 490 manure, experiment with 510 Mitscherlich . . . 116 Moisture removed by carbonic acid ..... 365 Motion converted into heat . 169 Multiple proportions . . . 96 Muriatic acid, its use . .145 Muscardine ..... 265 Mustard, oil of ... 223 NATURAL laws, importance of . 35 certainty of .483 Nature, balance of . . . 479 mode of investigating . 27 Nitrification . ... 239 Nitrogen compounds . . 395 Nutrition, plastic elements of . 378 in carnivora . . . 373 in gramiuivora . 373 PAGB 0. OBERTEIG, or upper dough . 464 Observation, art of . 28 Ocean, organic life in . .486 Organic atoms . . . . 201 how formed . 203 bases, nature of . . 473 bodies, decay of . . 206 compounds, formation of . . . .453 forces dependent on food . . . . 389 Organised bodies. . . . 193 Organs, mutual relation of . 353 Oxygen, consumed in respira- tion 341 Ozone produced by chemical action . . . . 189 Ozonised oxygen . . . Ib3 detection of .184 preparation of. 184 P. PELOUZE, letter of, on sponta- neous combustion . . 520 Perennial plants . . . . 490 Pettenkofer's wood-gas . .163 Phosphorus, an ozoniser . .184 Physical forces, action of . . 195 nature of . . 278 Physiological and chemical terms 273 Plants, food of, in air and soil. 489 Platinum, its value . . .125 spongy, action of .135 Precipitates . . 91 Pulmonary circulation . . 356 Putrefaction . . . . 208 R. RAYMOND LULLY . 74 Regnault, letter of, on sponta neous combustion . . 519 Rennet .... 22*5 Respiration and animal heat 342 food 341 Respiratory food . . 380, 396 carbon of . 401 INDEX. 535 PAGE Respiratory and plastic food daily consumed 475 Richter . 102 S. SALICINE 219 Saligenine . . . . . 219 Salt 99 endosmosis of its solution 431 good effects of, on animals 428 importance of, to the vital processes . . . . 425 physical properties of, im- portant . . . .477 Scabies 265 Schonbein .... 183 Science founded on experience 3 its three periods . . 60 Sciences, benefit of . . 477 connection of . . 270 Silicates, decomposed by lime 499 Soda, manufacture of . . . 141 Soil, function of . . .486 Soldier, daily ration of bread to 388 Soluble glass . . . .147 Solvents, use of, in analysis . 92 Sound and specific heat . . 329 Soup, ashes of ... 446 value of . . . . 440 for invalids . . . 525 - reason of its nutritive value . . . . 445 Specific gravity . . .118 heat . . . . 327 volumes . . . 123 Spheroidal state . . . . 132 Spontaneous combustion . .296 cases of . . 299 without proof . 301 theories of . 308 case from Debats 518 Stahl 57 Starch 382 action of gluten on . . 224 equivalent, how calcu- lated . . . .384 Starvation, phenomena of . . 349 Sugar, beet-root . . .158 cane .... 160 conversion into fat . 398 Sulphuric acid, manufacture of 143 PAQE Sulphuric acid, applications of 149 Sulphur-trade . . . . 152 Symbols, chemical . . . 9S Synthesis, chemical . . . 127 T. TABLE of chief constituents of the body . .454 nutritive value of food . . .452 - plastic and respira- tory food . . 384 relations of animal constituents . 454 respiratory food .402 Tea, action of . . . 471, 474 infusion, ashes of . . 474 contains iron . 474 Temperance societies, effects of 470 Theine 473 Theory and practice contrasted 30 Tortured animals, flesh of, bad 5 1 6 Tropical plants . . .490 Turpentine, oil of, ozonising action of . . . .187 U. ULTRAMARINE . . . .127 Universal medicine . 78 Universe, immensity of . .33 Universities, foundation of . 67 Upper dough of breweries nu- tritious . . . .464 Urine, composition of salts in animal's 423 in man . 418 salts found in . . .417 V. VEAL, salts of . . . . 449 Vegetable acids in blood . 421 albumen . . . 374 caseine . . . 375 fibrine . . . 374 Vital force . . 21,193,294 by whom denied . 286 536 INDEX. PAGE Vital force, phenomena not ex- plained by chemistry . . 272 Vitriol, oil of . . . . 143 W. WATER-GLASS . . . .147 Watt 58 Wine-making, improvements in 244 Wines, bouquet of . . .217 commercial value of .469 Wines, composition of Rhine . 469 manufacture of .241 value of Rhine . .469 Wood-gas for illumination . 163 Working miners, estimation of food of . . 521 Y. YOLK of Eggs, nutritious value of . . 447 ERRATUM. Page 236, line 11, for " and even " read " except. THE END. KVANS, PRINTERS, ..^ai- llfJEL RETURN CIRCULATION DEPARTMENT Main Library 198 Main Stacks LOAN PERIOD 1 HOME USE 2 3 4 5 6 ALL BOOKS MAY BE RECALLED AFTER 7 DAYS. Renewls and Recharges may be made 4 days prior to the due date. Books may be Renewed by calling 642-3405. DUE AS STAMPED BELOW FFB I 5 2001 due, 1 /j^la / / OCT 19 2003 APR 1 1 zo JB~ > UNIVERSITY OF CALIFORNIA, BERKELEY FORM NO. DD6 BERKELEY CA 94720-6000 . U.C.BERKELEY LIBRARIES - - ---n ,*?&* &