Oldalképek
PDF
ePub

Though the process of reasoning, which led to this analysis of sugar, is too hypothetical to be trusted implicitly, yet I am persuaded that it is to a certain degree correct, and that the result obtained does not deviate very far from the truth. If we compare Lavoisier's statement of the composition of sugar obtained in a different manner, though by a mode of reasoning not less hypothetical, we shall be surprised at its near coincidence with mine. His numbers are,

[blocks in formation]

It is true that two different hypotheses may lead to the same result, and yet be both wrong; but this becomes infinitely improbable in the present case, when we consider that the proportion of carbon, which I assign to sugar, must at all events be nearly correct.

We have no direct method of determining the weight of an integrant particle of sugar; but if the accuracy of the preceding analysis be admitted, it furnishes us with an indirect one, which cannot be rejected; for it is clear, that the atoms of oxygen, carbon, and hydrogen, will be to each other respectively, as the numbers *,

,; and these numbers reduced to their lowest terms become 5, 3, 4, nearly, which being primes with respect to each other, must represent the number of atoms, of which an integrant particle of sugar is composed. Sugar then is a compound of 12 atoms; namely, five of oxygen, three of carbon, and four of hydrogen; the weight of an integrant particle of it is 47.5, and its symbol is 53 c + 4h. It differs from oxalic acid

merely

merely in containing an additional atom of oxygen and two of hydrogen. If we had any method of removing these substances, without altering the proportion of the other constituents, we should obtain a much greater quantity of oxalic acid from sugar than we can at present; but nitric acid acts by removing one-half of the carbon in the form of carbonic acid; the sugar deprived of this, resolves itself into oxalic acid and water. Suppose two particles of sugar acted on at once, the symbol for them will be 10w + 6c+8 h. Let three atoms of the carbon be removed by the action of the nitric acid, there will remain 10w + 3 c +8 h. Now

[blocks in formation]

This will

which is just the quantity of oxalic acid left. give us some idea of the way in which the formation of oxalic acid by nitric acid is accomplished. And although the series of changes is probably more complicated, yet they are ultimately equivalent to the preceding statement. I allude to the formation of malic acid, which is said to precede the oxalic acid, and afterwards to be converted into it by the subsequent action of nitric acid; but on the composition and formation of this latter acid, I avoid making any observations at present, as I propose to make them the subject of a separate dissertation.

On

On Super-acid and Sub-acid Salts.

By WILLIAM HYDE WOLLASTON, M. D. Sec. R. S.

IN the paper which has just been read to the Society,

Dr. Thomson has remarked, that oxalic acid unites to strontian as well as to potash in two different proportions, and that the quantity of acid combined with each of these bases in their super-oxalates, is just double of that which is saturated by the same quantity of base in their neutral compounds.

[ocr errors]

As I had observed the same law to prevail in various other instances of super-acid and sub-acid salts, I thought it not unlikely that this law might obtain generally in such compounds, and it was my design to have pursued the subject with the hope of discovering the cause to which so regular a relation might be ascribed.

But since the publication of Mr. Dalton's theory of chemical combination, as explained and illustrated by Dr. Thomson*, the inquiry which I had designed appears to be superfluous, as all the facts that I had observed are but particular instances of the more general observation of Mr. Dalton, that in all cases the simple elements of bodies are disposed to unite atom to atom singly, or, if either is in excess, it exceeds by a ratio to be expressed by some simple multiple of the number of its atoms.

However, since those who are desirous of ascertaining the justness of this observation by experiment, may be deterred by the difficulties that we meet with in attempting to determine with precision the constitution of gaseous bodies, for the explanation of which Mr. Dalton's

* Thomson's Chemistry, third Edit. vol. III. p. 425. VOL. XHI-SECOND SERIES. Ggg

theory

theory was first conceived, and since some persons may imagine that the results of former experiments on such bodies do not accord sufficiently to authorize the adoption of a new hypothesis, it may be worth while to describe a few experiments, each of which may be performed with the utmost facility, and each of which affords the most direct proof of the proportional redundance or deficiency of acid in the several salts employed.

Sub-carbonate of Potash.

Exp. 1. Sub-carbonate of potash recently prepared, is one instance of an alkali having one-half the quantity of acid necessary for its saturation, as may thus be satisfactorily proved.

Let two grains of fully saturated and well crystallized carbonate of potash be wrapped in a piece of thin paper, and passed up into an inverted tube filled with mercury, and let the gas be extricated from it by a sufficient quantity of muriatic acid, so that the space it occupies may be marked upon the tube.

Next, let four grains of the same carbonate be exposed for a short time to a red heat; and it will be found to have parted with exactly half its gas; for the gas extricated from it in the same apparatus will be found to occupy exactly the same space, as the quantity before obtained from two grains of fully saturated carbonate.

[blocks in formation]

Exp. 2. A similar experiment may be made with a saturated carbonate of soda, and with the same result; for this also becomes a true semi-carbonate by being exposed for a short time to a red heat,

Super

Super-sulphate of Potash.

By an experiment equally simple, super-sulphate of potash may be shewn to contain exactly twice as much acid as is necessary for the mere saturation of the alkali present.

Exp. 3. Let twenty grains of carbonate of potash (which would be more than neutralized by ten grains of sulphuric acid) be mixed with about twenty-five grains of that acid in a covered crucible of platina, or in a. glass tube three quarters of an inch diameter, and five, or six inches long.

By heating this mixture till it ceases to boil, and begins to appear slightly red hot, a part of the redundant acid will be expelled, and there will remain a determinate quantity forming super-sulphate of potash, which when dissolved in water will be very nearly neutralized by an addition of twenty grains more of the same carbonate of potash; but it is generally found very slightly acid, in consequence of the small quantity of sulphuric acid which remains in the vessel in a gaseous

state at a red heat.

In the preceding experiments, the acids are made to assume a determinate proportion to their base, by heat which cannot destroy them. In those which follow, the proportion which a destructible acid shall assume cannot be regulated by the same means; but the constitution of its compounds previously formed, may nevertheless be proved with equal facility.

Super-oxalate of Potash.

Exp. 4. The common super-oxalate of potash is a salt that contains alkali sufficient to saturate exactly half of Ggg 2

the

« ElőzőTovább »