Elements of Chemistry Part 6

Caloric retained by each lib. of water at the temperature of Zero (32), 12.32823.

_Of the Formation of Nitric Acid._

When we combine nitrous gas with oxygen gas, so as to form nitric or nitrous acid a degree of heat is produced, which is much less considerable than what is evolved during the other combinations of oxygen; whence it follows that oxygen, when it becomes fixed in nitric acid, retains a great part of the heat which it possessed in the state of gas. It is certainly possible to determine the quant.i.ty of caloric which is disengaged during the combination of these two ga.s.ses, and consequently to determine what quant.i.ty remains after the combination takes place. The first of these quant.i.ties might be ascertained, by making the combination of the two ga.s.ses in an apparatus surrounded by ice; but, as the quant.i.ty of caloric disengaged is very inconsiderable, it would be necessary to operate upon a large quant.i.ty of the two ga.s.ses in a very troublesome and complicated apparatus. By this consideration, Mr de la Place and I have hitherto been prevented from making the attempt. In the mean time, the place of such an experiment may be supplied by calculations, the results of which cannot be very far from truth.

Mr de la Place and I deflagrated a convenient quant.i.ty of nitre and charcoal in an ice apparatus, and found that twelve pounds of ice were melted by the deflagration of one pound of nitre. We shall see, in the sequel, that one pound of nitre is composed, as under, of

Potash 7 oz. 6 gros 51.84 grs. = 4515.84 grs.

Dry acid 8 1 21.16 = 4700.16.

The above quant.i.ty of dry acid is composed of

Oxygen 6 oz. 3 gros 66.34 grs. = 3738.34 grs.

Azote 1 5 25.82 = 961.82.

By this we find that, during the above deflagration, 2 gros 1-1/3 gr. of charcoal have suffered combustion, alongst with 3738.34 grs.

or 6 oz. 3 gros 66.34 grs. of oxygen. Hence, since 12 libs. of ice were melted during the combustion, it follows, that one pound of oxygen burnt in the same manner would have melted 29.58320 libs. of ice. To which the quant.i.ty of caloric, retained by a pound of oxygen after combining with charcoal to form carbonic acid gas, being added, which was already ascertained to be capable of melting 29.13844 libs.

of ice, we have for the total quant.i.ty of caloric remaining in a pound of oxygen, when combined with nitrous gas in the nitric acid 58.72164; which is the number of pounds of ice the caloric remaining in the oxygen in that state is capable of melting.

We have before seen that, in the state of oxygen gas, it contained at least 66.66667; wherefore it follows that, in combining with azote to form nitric acid, it only loses 7.94502. Farther experiments upon this subject are necessary to ascertain how far the results of this calculation may agree with direct fact. This enormous quant.i.ty of caloric retained by oxygen in its combination into nitric acid, explains the cause of the great disengagement of caloric during the deflagrations of nitre; or, more strictly speaking, upon all occasions of the decomposition of nitric acid.

_Of the Combustion of Wax._

Having examined several cases of simple combustion, I mean now to give a few examples of a more complex nature. One pound of wax-taper being allowed to burn slowly in an ice apparatus, melted 133 libs. 2 oz.

5-1/3 gros of ice. According to my experiments in the Memoirs of the Academy for 1784, p. 606, one pound of wax-taper consists of 13 oz. 1 gros 23 grs. of charcoal, and 2 oz. 6 gros 49 grs. of hydrogen.

By the foregoing experiments, the above quant.i.ty of charcoal ought to melt 79.39390 libs. of ice; and the hydrogen should melt 52.37605 --------- In all 131.76995 libs.

Thus, we see the quant.i.ty of caloric disengaged from a burning taper, is pretty exactly conformable to what was obtained by burning separately a quant.i.ty of charcoal and hydrogen equal to what enters into its composition. These experiments with the taper were several times repeated, so that I have reason to believe them accurate.

_Combustion of Olive Oil._

We included a burning lamp, containing a determinate quant.i.ty of olive-oil, in the ordinary apparatus, and, when the experiment was finished, we ascertained exactly the quant.i.ties of oil consumed, and of ice melted; the result was, that, during the combustion of one pound of olive-oil, 148 libs. 14 oz. 1 gros of ice were melted. By my experiments in the Memoirs of the Academy for 1784, and of which the following Chapter contains an abstract, it appears that one pound of olive-oil consists of 12 oz. 5 gros 5 grs. of charcoal, and 3 oz. 2 gros 67 grs. of hydrogen. By the foregoing experiments, that quant.i.ty of charcoal should melt 76.18723 libs. of ice, and the quant.i.ty of hydrogen in a pound of the oil should melt 62.15053 libs.

The sum of these two gives 138.33776 libs. of ice, which the two const.i.tuent elements of the oil would have melted, had they separately suffered combustion, whereas the oil really melted 148.88330 libs.

which gives an excess of 10.54554 in the result of the experiment above the calculated result, from data furnished by former experiments.

This difference, which is by no means very considerable, may arise from errors which are unavoidable in experiments of this nature, or it may be owing to the composition of oil not being as yet exactly ascertained. It proves, however, that there is a great agreement between the results of our experiments, respecting the combination of caloric, and those which regard its disengagement.

The following desiderata still remain to be determined, viz. What quant.i.ty of caloric is retained by oxygen, after combining with metals, so as to convert them into oxyds; What quant.i.ty is contained by hydrogen, in its different states of existence; and to ascertain, with more precision than is. .h.i.therto attained, how much caloric is disengaged during the formation of water, as there still remain considerable doubts with respect to our present determination of this point, which can only be removed by farther experiments. We are at present occupied with this inquiry; and, when once these several points are well ascertained, which we hope they will soon be, we shall probably be under the necessity of making considerable corrections upon most of the results of the experiments and calculations in this Chapter. I did not, however, consider this as a sufficient reason for withholding so much as is already known from such as may be inclined to labour upon the same subject. It is difficult, in our endeavours to discover the principles of a new science, to avoid beginning by guess-work; and it is rarely possible to arrive at perfection from the first setting out.

CHAP. X.

_Of the Combination of Combustible Substances with each other._

As combustible substances in general have a great affinity for oxygen, they ought likewise to attract, or tend to combine with each other; _quae sunt eadem uni tertio, sunt eadem inter se_; and the axiom is found to be true. Almost all the metals, for instance, are capable of uniting with each other, and forming what are called _alloys_[22], in common language. Most of these, like all combinations, are susceptible of several degrees of saturation; the greater number of these alloys are more brittle than the pure metals of which they are composed, especially when the metals alloyed together are considerably different in their degrees of fusibility. To this difference in fusibility, part of the phenomena attendant upon _alloyage_ are owing, particularly the property of iron, called by workmen _hotshort_. This kind of iron must be considered as an alloy, or mixture of pure iron, which is almost infusible, with a small portion of some other metal which fuses in a much lower degree of heat. So long as this alloy remains cold, and both metals are in the solid state, the mixture is malleable; but, if heated to a sufficient degree to liquify the more fusible metal, the particles of the liquid metal, which are interposed between the particles of the metal remaining solid, must destroy their continuity, and occasion the alloy to become brittle. The alloys of mercury, with the other metals, have usually been called _amalgams_, and we see no inconvenience from continuing the use of that term.

Sulphur, phosphorus, and charcoal, readily unite with metals.

Combinations of sulphur with metals are usually named _pyrites_. Their combinations with phosphorus and charcoal are either not yet named, or have received new names only of late; so that we have not scrupled to change them according to our principles. The combinations of metal and sulphur we call _sulphurets_, those with phosphorus _phosphurets_, and those formed with charcoal _carburets_. These denominations are extended to all the combinations into which the above three substances enter, without being previously oxygenated. Thus, the combination of sulphur with potash, or fixed vegetable alkali, is called _sulphuret of potash_; that which it forms with ammoniac, or volatile alkali, is termed _sulphuret of ammoniac_.

Hydrogen is likewise capable of combining with many combustible substances. In the state of gas, it dissolves charcoal, sulphur, phosphorus, and several metals; we distinguish these combinations by the terms, _carbonated hydrogen gas_, _sulphurated hydrogen gas_, and _phosphorated hydrogen gas_. The sulphurated hydrogen gas was called _hepatic air_ by former chemists, or _foetid air from sulphur_, by Mr Scheele. The virtues of several mineral waters, and the foetid smell of animal excrements, chiefly arise from the presence of this gas. The phosphorated hydrogen gas is remarkable for the property, discovered by Mr Gengembre, of taking fire spontaneously upon getting into contact with atmospheric air, or, what is better, with oxygen gas. This gas has a strong flavour, resembling that of putrid fish; and it is very probable that the phosph.o.r.escent quality of fish, in the state of putrefaction, arises from the escape of this species of gas. When hydrogen and charcoal are combined together, without the intervention of caloric, to bring the hydrogen into the state of gas, they form oil, which is either fixed or volatile, according to the proportions of hydrogen and charcoal in its composition. The chief difference between fixed or fat oils drawn from vegetables by expression, and volatile or essential oils, is, that the former contains an excess of charcoal, which is separated when the oils are heated above the degree of boiling water; whereas the volatile oils, containing a just proportion of these two const.i.tuent ingredients, are not liable to be decomposed by that heat, but, uniting with caloric into the ga.s.seous state, pa.s.s over in distillation unchanged.

In the Memoirs of the Academy for 1784, p. 593. I gave an account of my experiments upon the composition of oil and alkohol, by the union of hydrogen with charcoal, and of their combination with oxygen. By these experiments, it appears that fixed oils combine with oxygen during combustion, and are thereby converted into water and carbonic acid. By means of calculation applied to the products of these experiments, we find that fixed oil is composed of 21 parts, by weight, of hydrogen combined with 79 parts of charcoal. Perhaps the solid substances of an oily nature, such as wax, contain a proportion of oxygen, to which they owe their state of solidity. I am at present engaged in a series of experiments, which I hope will throw great light upon this subject.

It is worthy of being examined, whether hydrogen in its concrete state, uncombined with caloric, be susceptible of combination with sulphur, phosphorus, and the metals. There is nothing that we know of, which, _a priori_, should render these combinations impossible; for combustible bodies being in general susceptible of combination with each other, there is no evident reason for hydrogen being an exception to the rule: However, no direct experiment as yet establishes either the possibility or impossibility of this union. Iron and zinc are the most likely, of all the metals, for entering into combination with hydrogen; but, as these have the property of decomposing water, and as it is very difficult to get entirely free from moisture in chemical experiments, it is hardly possible to determine whether the small portions of hydrogen gas, obtained in certain experiments with these metals, were previously combined with the metal in the state of solid hydrogen, or if they were produced by the decomposition of a minute quant.i.ty of water. The more care we take to prevent the presence of water in these experiments, the less is the quant.i.ty of hydrogen gas procured; and, when very accurate precautions are employed, even that quant.i.ty becomes hardly sensible.

However this inquiry may turn out respecting the power of combustible bodies, as sulphur, phosphorus, and metals, to absorb hydrogen, we are certain that they only absorb a very small portion; and that this combination, instead of being essential to their const.i.tution, can only be considered as a foreign substance, which contaminates their purity.

It is the province of the advocates[23] for this system to prove, by decisive experiments, the real existence of this combined hydrogen, which they have hitherto only done by conjectures founded upon suppositions.

FOOTNOTES:

[22] This term _alloy_, which we have from the language of the arts, serves exceedingly well for distinguishing all the combinations or intimate unions of metals with each other, and is adopted in our new nomenclature for that purpose.--A.

[23] By these are meant the supporters of the phlogistic theory, who at present consider hydrogen, or the base of inflammable air, as the phlogiston of the celebrated Stahl.--E.

CHAP. XI.

_Observations upon Oxyds and Acids with several Bases--and upon the Composition of Animal and Vegetable Substances._

We have, in Chap. V. and VIII. examined the products resulting from the combustion of the four simple combustible substances, sulphur, phosphorus, charcoal, and hydrogen: We have shown, in Chap. X that the simple combustible substances are capable of combining with each other into compound combustible substances, and have observed that oils in general, and particularly the fixed vegetable oils, belong to this cla.s.s, being composed of hydrogen and charcoal. It remains, in this chapter, to treat of the oxygenation of these compound combustible substances, and to show that there exist acids and oxyds having double and triple bases. Nature furnishes us with numerous examples of this kind of combinations, by means of which, chiefly, she is enabled to produce a vast variety of compounds from a very limited number of elements, or simple substances.

It was long ago well known, that, when muriatic and nitric acids were mixed together, a compound acid was formed, having properties quite distinct from those of either of the acids taken separately. This acid was called _aqua regia_, from its most celebrated property of dissolving gold, called _king of metals_ by the alchymists. Mr Berthollet has distinctly proved that the peculiar properties of this acid arise from the combined action of its two acidifiable bases; and for this reason we have judged it necessary to distinguish it by an appropriate name: That of _nitro-muriatic_ acid appears extremely applicable, from its expressing the nature of the two substances which enter into its composition.

This phenomenon of a double base in one acid, which had formerly been observed only in the nitro-muriatic acid, occurs continually in the vegetable kingdom, in which a simple acid, or one possessed of a single acidifiable base, is very rarely found. Almost all the acids procurable from this kingdom have bases composed of charcoal and hydrogen, or of charcoal, hydrogen, and phosphorus, combined with more or less oxygen.

All these bases, whether double or triple, are likewise formed into oxyds, having less oxygen than is necessary to give them the properties of acids. The acids and oxyds from the animal kingdom are still more compound, as their bases generally consist of a combination of charcoal, phosphorus, hydrogen, and azote.

As it is but of late that I have acquired any clear and distinct notions of these substances, I shall not, in this place, enlarge much upon the subject, which I mean to treat of very fully in some memoirs I am preparing to lay before the Academy. Most of my experiments are already performed; but, to be able to give exact reports of the resulting quant.i.ties, it is necessary that they be carefully repeated, and increased in number: Wherefore, I shall only give a short enumeration of the vegetable and animal acids and oxyds, and terminate this article by a few reflections upon the composition of vegetable and animal bodies.

Sugar, mucus, under which term we include the different kinds of gums, and starch, are vegetable oxyds, having hydrogen and charcoal combined, in different proportions, as their radicals or bases, and united with oxygen, so as to bring them to the state of oxyds. From the state of oxyds they are capable of being changed into acids by the addition of a fresh quant.i.ty of oxygen; and, according to the degrees of oxygenation, and the proportion of hydrogen and charcoal in their bases, they form the several kinds of vegetable acids.

It would be easy to apply the principles of our nomenclature to give names to these vegetable acids and oxyds, by using the names of the two substances which compose their bases: They would thus become hydro-carbonous acids and oxyds: In this method we might indicate which of their elements existed in excess, without circ.u.mlocution, after the manner used by Mr Rouelle for naming vegetable extracts: He calls these extracto-resinous when the extractive matter prevails in their composition, and resino-extractive when they contain a larger proportion of resinous matter. Upon that plan, and by varying the terminations according to the formerly established rules of our nomenclature, we have the following denominations: Hydro-carbonous, hydro-carbonic; carbono-hydrous, and carbono-hydric oxyds. And for the acids: Hydro-carbonous, hydro carbonic, oxygenated hydro-carbonic; carbono-hydrous, carbono-hydric, and oxygenated carbono-hydric. It is probable that the above terms would suffice for indicating all the varieties in nature, and that, in proportion as the vegetable acids become well understood, they will naturally arrange themselves under these denominations. But, though we know the elements of which these are composed, we are as yet ignorant of the proportions of these ingredients, and are still far from being able to cla.s.s them in the above methodical manner; wherefore, we have determined to retain the ancient names provisionally. I am somewhat farther advanced in this inquiry than at the time of publishing our conjunct essay upon chemical nomenclature; yet it would be improper to draw decided consequences from experiments not yet sufficiently precise: Though I acknowledge that this part of chemistry still remains in some degree obscure, I must express my expectations of its being very soon elucidated.

I am still more forcibly necessitated to follow the same plan in naming the acids, which have three or four elements combined in their bases; of these we have a considerable number from the animal kingdom, and some even from vegetable substances. Azote, for instance, joined to hydrogen and charcoal, form the base or radical of the Prussic acid; we have reason to believe that the same happens with the base of the Gallic acid; and almost all the animal acids have their bases composed of azote, phosphorus, hydrogen, and charcoal. Were we to endeavour to express at once all these four component parts of the bases, our nomenclature would undoubtedly be methodical; it would have the property of being clear and determinate; but this a.s.semblage of Greek and Latin substantives and adjectives, which are not yet universally admitted by chemists, would have the appearance of a barbarous language, difficult both to p.r.o.nounce and to be remembered. Besides, this part of chemistry being still far from that accuracy it must arrive to, the perfection of the science ought certainly to precede that of its language; and we must still, for some time, retain the old names for the animal oxyds and acids. We have only ventured to make a few slight modifications of these names, by changing the termination into _ous_, when we have reason to suppose the base to be in excess, and into _ic_, when we suspect the oxygen predominates.

The following are all the vegetable acids. .h.i.therto known:

1. Acetous acid.

2. Acetic acid.

3. Oxalic acid.