No. 1105.

NOVEMBER 2, 1844.

LECTURESON

ORGANIC CHEMISTRY:DELIVERED DURING THE WINTER SESSION, 1844, IN THE

University of Giessen.

BY JUSTUS LIEBIG, M.D., PH. D., F.R.S., M.R.I.A.,Professor of Chemistry in the University of Giessen.

OXALIC ACID.

GENTLEMEN,-In the last lecture, I had occasion to mentionsome very curious and interesting facts relative to the formationof OXALIC ACID, in the process employed for the production ofpotassium, and from the solution of oxicarburet of potassium inwater. Now oxalic acid is very extensively diffused throughoutorganic nature, as a production of vegetable life. It is found toexist in plants, generally in the form of an acid salt with an alka-Tine base, or also-and this especially in the roots of plants-incombination with lime, to a very considerable amount. Oxalateof lime forms so large a proportion of certain lichens as frequentlyto amount to half their weight when in a dry state. Theflaments of the chick-pea, (cicer arietinum,) when subjected toexpression, yield clear drops of juice, which, according to theobservations of Klaproth, contain pure oxalic acid. The commonwood sorrel (oxalis acetosella) is particularly rich in binoxalateof potass. Oxalate of potass, for commercial purposes, was fora long time prepared from that plant, which grows in greatabundance in Switzerland; but after Scheele discovered thatoxalic acid could be artificially formed from many organic sub- Istances by means of nitric acid, the low price of the latter acidsoon induced chemists to adopt this method for the preparation ofoxalic acid upon a large scale. Potato -starch, or grain-starch,and sugar, are mixed with from eight to ten times their weight ofnitric acid, in stone-ware vessels, and heated in a water-bath:solution takes place readily with the evolution of nitrous acid;after concentration and refrigeration, crystallized oxalic acid isyielded, to the amount of one-sixth part of the weight of the3naterials employed.A further amount of oxalic acid may be obtained by adding

nitric acid to the remaining mother-liquor, and repeating thesame operation. This method of preparing oxalic acid is usuallypractised in sulphuric acid manufactories, when the nitrous acidevolved in the course of the process finds a special application forthe conversion of sulphurous acid into sulphuric acid. Wood-fibre, and a number of organic substances, may be acted on by-nitric acid in a similar manner as starch and sugar; if oxygen issupplied to them at a temperature not exceeding the boiling pointof water, the largest proportion of their carbon is obtained in the"form of oxalic acid; but at the boiling point of nitric acid, theoxalic acid absorbs a fresh quantity of oxygen, and is therebyconverted into carbonic acid. I have already mentioned thatthe carbon of organic substances is likewise obtained as oxalicacid, by keeping these substances in fusion, together withcaustic potass or soda, up to a certain point, indicated by theevolution of an inflammable gas, with frothing of the fusingmass. Gregory has observed that sugar in aqueous solution,when heated together with hypermanganate of potass, is con-verted into neutral oxalate of potass, with precipitation of peroxide- of manganese.The crystallized oxalic acid loses at 212° 14 per cent. of water,

(two atoms,) whilst its crystals crumble into a white powder.At a temperature above 212°, in open vessels, it fuses and vola-tilizes, forming white vapour. Distilled in a retort, it undergoesdecomposition, and is converted into carbonic acid, carbonicoxide, and formic acid.A principal means of detecting oxalic acid and the oxalates is

afforded by their deportment with concentrated sulphuric acid;crystallized oxalic acid, as well as its salts, dissolve in concen-trated sulphuric acid at an elevated temperature, and this solu-tion, upon continued application of heat, evolves, with all thephenomena usually attendant upon boiling, a gas which burnswith a blue flame, and produces in lime-water a precipitate ofcarbonate of lime: this gas consists of a mixture of equal volumesof carbonic oxide gas and carbonic acid gas. No charring ofthe oxalic acid, nor evolution of sulphurous acid, occurs in thisdecomposition. Other organic acids, such as citric acid, formicacid, &c. &c., evolve likewise carbonic oxide gas upon beingheated with sulphuric acid; but citric acid gets charred in theoperation, and the process, moreover, is attended with evolution of

sulphurous acid; whilst the carbonic oxide gas evolved fromformic acid-wbich undergoes no charring in this operation-is pure from any admixture of carbonic acid gas. This methodof decomposition (heating with concentrated sulphuric acid)affords us, therefore, a simple and certain means of detectingoxalic acid, and of distinguishing it from all other organic acids.Oxalic acid possesses a very acid taste ; it acts upon the livingorganism as a strong poison; in cases where half an ounceof oxalic acid has been administered by mistake, instead of £Epsom salts-to which it bears a strong resemblance in its exter-nal appearance-death has ensued. Alkalies, magnesia, and car-bonate of lime, are the most sure and effective antidotes in casesof poisoning with oxalic acid.Dry oxalic acid-i. e., oxalic acid from which the two atoms

of constitutional water have been expelled by heat, thurs leavingonly the one atom of basic water-is constituted according to theformula C2 04 H, or C2 03 + H 0. From this formula it will beseen at once that it contains the elements of carbonic acid, plusone equivalent of hydrogen. If the hydrogen is removed, or if oneatom of oxygen is made to combine with the so-called anhydrousacid, two atoms of carbonic acid are formed out of one atom ofoxalic acid. This will readily explain the mode of formation ofoxalic acid in plants : it is formed out of carbonic acid, whichis absorbed by the leaves, and, water being present, is de-

composed through the co-operation of light. The elements oftwo atoms of carbonic acid are combined with the elements ofone atom of water, the oxygen of which is exhaled as gas by theleaves.

From this formula it will be seen that these salts contain oneequivalent of metal and the elements of two atoms of carbonicacid. This composition explains their deportment when exposedto the action of fire. The oxalates of nickel, of copper, of lead, ofsilver, and in general those with easily reducible metals, leavethese metals, upon the application of a red heat, in their puremetallic state. Thus, for instance, by exposing oxalate of nickelin a crucible to a red heat in a porcelain stove, a fine regulus ofnickel is obtained, particularly free from carbon. All the carbonof the oxalic acid is evolved as carbonic acid. The oxalates withalkaline bases, with potass, lime, &c. &c., yield, upon beingexposed to a red heat, inflammable carbonic oxide gas, and areconverted into carbonates, either without changing their colour,or transitorily assuming a charred appearance, which very rapidlyvanishes.

C O3, K = carbonate of potassOxalate of potass, C, 0,, {C O = carbonate oxide gas.This deportment under the influence of a red heat, distinguishesthis class of salts from the salts of other organic acids: most saltswith organic acids get charred at a red heat: several of theacetates are exceptions to this rule, since they behave themselveslike the oxalates.The salt of sorrel formerly occurring in commerce, was

binoxalate of potass. This salt contains two atoms of anhydrousoxalic acid, one atom of potass, and three atoms of water. If youdivide a certain amount of binoxalate of potass into two equalportions, by means of the balance, destroy the one portion by theapplication of a red heat, and then add the residue to the solutionof the other portion, you will obtain an exactly neutral fluid. It

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is by means of this process that you may determine whether youhave really binoxalate of potass or not.The salt which is met with principally in commerce at the pre-

sent time, contains four atoms of oxalic acid, one atom of potass,and seven atoms of water, and thus only half as much potass andone atom of water more than the true binoxalate. In order torender this salt neutral, it is necessary to divide the crystallizedsalt into four equal parts, by means of the balance, to exposethree parts to the action of a red heat, and to add the residue tothe solution of the fourth part.

Oxalate of lime is one of the least soluble of the limeSalts, and it is on this account that the soluble oxalates, and

especially oxalate of ammonia, are used as a means of precipi-tating lime from fluids; the precipitate of oxalate of lime isthrown down in the shape of fine flakes; it is dried, and heated toredness; there remains a white residue of carbonate of lime, fromwhich the proportion of lime may be inferred. Considering,however, that carbonate of lime in a state of red heat readilyloses carbonic acid, it is advisable to transform the residue ofcarbonate of lime into sulphate of lime, by moistening it withsulphuric acid, and then to deduce the proportion of lime fromthis gypsum after it has been heated to redness. In fluids con-taining lime and at the same time free nitric acid, or free hydro-chloric acid, no precipitate is obtained by means of oxalic acid orof oxalates, since the oxalate of lime which forms upon the addi-tion of this acid or of these salts to the calcareous fluid, dissolvesreadily in these acids ; however, upon neutralizing the latter,especially with application of heat, the oxalate of lime is com-pletely precipitated. Acetic acid does not dissolve oxalate oflime. Oxalic acid forms a very remarkable double salt withoxide of chromium and potass; the oxalate of chromium andpotass was discovered by Dr. Gregory. The crystals of this saltare of such a deep colour as to appear black, (by reflected light,)but they appear of a splendid blue by transmitted light, (whensufficiently thin to be transparent;) their solution appears green byreflected light, and red by transmitted light.

It is to Professor Graham that we are chiefly indebted for ourknowledge of the composition of these salts.

I have already mentioned that oxalic acid, whether free or inits salts, is converted into carbonic acid by the addition of

oxygen. In order to obtain the carbon of oxalic acid, as car-

bonic acid, you require one equivalent of oxygen to one equiva-lent of oxalic acid; - the result is, the formation of two atoms ofcarbonic acid. The knowledge of these proportions is of import-ance, since a method has been based thereon to determine theamount of oxygen contained in certain oxides, by inferring itfrom the amount of carbonic acid formed of oxalic acid by theabsorption of oxygen from the oxide under investigation. Indeed,if you once know the amount of carbonic acid evolved from amixture of oxalic acid with a metallic oxide, you can readily de-termine the amount of oxygen which the oxide has yielded. If,for instance, you take finely pounded peroxide of manganese, andheat it together with a solution of oxalic-acid, there ensues a vivideffervescence, owing to the evolution of carbonic acid; the

peroxide of manganese changes from black to a yellowish-whitehue, being converted into oxalate of the protoxide of manganese.The evolution of carbonic acid, and reduction of the peroxideinto the protoxide of manganese, are easily explained. The peroxideof manganese to be converted into protoxide must yield upoxygen, and this oxygen combines with the element of oxalicacid; for every equivalent of oxygen yielded by the peroxide ofmanganese, you obtain two equivalents of carbonic acid. Now if

you know the amount of carbonic acid thus produced, you knowalso the amount of oxygen which the peroxide of manganese hasyielded in its reduction to protoxide. Peroxide of manganesecontains to one atom of manganese two atoms of oxygen, andone of these two atoms separates upon its reduction into prot-4oxide.The weight of one equivalent of peroxide of manganese is

== 44, (one atom of manganese = 28; two atoms of oxygen z 16.)Upon heating peroxide of manganese together with oxalic acid,there are formed 44 of carbonic acid, (two equivalents of C == 12;four equivalents of oxygen === 32.) A mixture of 100 grains ofpure peroxide of manganese with oxalic acid ought therefore,upon heating, to suffer a loss of weight of 100; it is obvious thata lesser amount of carbonic acid is obtained from the common

manganese ores, because they contain extraneous minerals,peroxide of iron, alumina, &c., in admixture; but the proportionof weight of the carbonic acid evolved from a mixture of 100parts of manganese ore with oxalic acid, indicates invariably, andwith positive certainty, the amount of peroxide contained in themanganese ore, and thus we ascertain its commercial value. Ifyou, for example, obtain from 100 parts of manganese ore, 90parts of carbonic acid, the ore contains only 90 parts of peroxide.

FOREIGN DEPARTMENT.

PHYSIOLOGICAL & PATHOLOGICAL RESEARCHESON TUBERCULOSIS.

By H. LEBERT, M.D.(Muller’s Archives, Nos. 2 and 3. 1844.)

THE following is the summary appended to this very valuablepaper :-

1. The pathological peculiarities of tubercle are exhibited inits microscopical structure.

2. The constant elements of tubercle are, molecular granules,an adhesive hyaline mass, and peculiar tubercle cells, from 0.05to 0.01 of a millimetre in diameter-of irregular form, containingno nucleus but molecular granules. Water, sether, and weak acid,scarcely change them. Concentrated alkalies, liq. ammoniee,dissolve them completely.

3. The dimensions of tubercle cells undergo many variations,which depend rather upon the different organs than upon differ-ences of age. They are most easily recognised in crude yellowtubercle.

4. Tubercle corpuscles consist of cells having a very low powerof development.

5. The opinion that tubercular substance is a modification ofpus is contradicted in the most positive manner by the micro-scope.

6. Tubercle corpuscles are distinguished from undeveloped pusglobules, by the spherical form and greater diameter of the latter.Cancer cells are clearly distinguished by their being two to fourtimes as large, and consisting of a cell wall, and a large clear nu-cleus, often containing nucleoli.

7. When tubercle softens, the adhesive matter becomes fluid,and the corpuscles rounded; their opposition to each other isdestroyed, they become distended, and hence appear larger.This, however, is not the result of growth, but the beginning ofdecay.

8. The pus which surrounds softened tubercle never origi-nates in the tubercle itself, but is formed directly in the surrounding parts.

9. The microscope can determine whether we have to do withsoftened tubercle, with purulent matter, or whether there be amixture of both.

10. Pus appears to destroy quickly tubercle corpuscles, andthus to make their individuality undistinguishable.

11. When the irregular outline and close apposition of tuberclecells, in their first stage of development, present the second stageof separation from each other, distention and roundness, then thethird stage of disintegration commences. The corpuscles arebroken up into a granular, half-fluid mass, and lose their in-dividuality.

12. Tubercle becoming hard and calcareous (etat cretacé) is anatural process of cure. The peculiar elements of tubercle dis-appear, and become in part absorbed. In their place, smallmineral granules, and sometimes crystals of cholesterine, are de-posited. The deposition of lime is generally accompanied by anincrease of pigment. According to the chemical analysis ofM. T. Boudet, there exist, as principal elements, chlorate of sodium,and sulphate of soda; salts of lime only in small quantity.

13. Among the occasional elements of tubercle may be men-tioned melanosis, which is the most frequent; further, fat, fila-ments, dark olive-coloured globules, and crystals. Sometimes wefind mixed with tubercle, but in no way belonging to its sub-stance, the products of inflammation, serum, pus, and the elementsof epithelium in various forms.

14. The seat of tubercle in the lungs is generally the elasticcellular tissue. Yet it is also found in the air vesicles, and in thebronchial capillaries.

15. The tissue of the lung surrounding tubercle may be sound,but is mostly in a state of congestion or inflammation. The lastis either globular, or spread over a large portion of a lobe.

16. The pus found surrounding tubercle is often not the resultof grey hepatization, but comes from the mucous membrane of the

small, partly destroyed and open bronchi, in the substance of thelung.

.

17. The pneumonia surrounding tubercles has nothing spe-cific ; there is found in it the same elements of the exudation as.in ordinary pneumonia-viz., aggregate globules, fat vesicles, puscorpuscles, &c. Tubercle corpuscles are not generally foundamong the products of exudation.

18. Sometimes there is found surrounding tubercle a peculiarform of chronic inflammation, with yellowish hepatization, andincreased consistence of the tissue. The vesicles of the lung,