Elements of Chemistry Part 5

Having adjusted every thing properly, as above directed, the tube H h is adapted to an air-pump, and the baloon A is exhausted of its air. We next admit the oxygen gas so as to fill the baloon, and then, by means of pressure, as is before mentioned, force a small stream of hydrogen gas through its tube D d', which we immediately set on fire by an electric spark. By means of the above described apparatus, we can continue the mutual combustion of these two ga.s.ses for a long time, as we have the power of supplying them to the baloon from their reservoirs, in proportion as they are consumed. I have in another place[20] given a description of the apparatus used in this experiment, and have explained the manner of ascertaining the quant.i.ties of the ga.s.ses consumed with the most scrupulous exact.i.tude.

In proportion to the advancement of the combustion, there is a deposition of water upon the inner surface of the baloon or matra.s.s A: The water gradually increases in quant.i.ty, and, gathering into large drops, runs down to the bottom of the vessel. It is easy to ascertain the quant.i.ty of water collected, by weighing the baloon both before and after the experiment. Thus we have a twofold verification of our experiment, by ascertaining both the quant.i.ties of the ga.s.ses employed, and of the water formed by their combustion: These two quant.i.ties must be equal to each other. By an operation of this kind, Mr Meusnier and I ascertained that it required 85 parts, by weight, of oxygen, united to 15 parts of hydrogen, to compose 100 parts of water. This experiment, which has not hitherto been published, was made in presence of a numerous committee from the Royal Academy. We exerted the most scrupulous attention to its accuracy; and have reason to believe that the above propositions cannot vary a two hundredth part from absolute truth.

From these experiments, both a.n.a.lytical and synthetic, we may now affirm that we have ascertained, with as much certainty as is possible in physical or chemical subjects, that water is not a simple elementary substance, but is composed of two elements, oxygen and hydrogen; which elements, when existing separately, have so strong affinity for caloric, as only to subsist under the form of gas in the common temperature and pressure of our atmosphere.

This decomposition and recomposition of water is perpetually operating before our eyes, in the temperature of the atmosphere, by means of compound elective attraction. We shall presently see that the phenomena attendant upon vinous fermentation, putrefaction, and even vegetation, are produced, at least in a certain degree, by decomposition of water.

It is very extraordinary that this fact should have hitherto been overlooked by natural philosophers and chemists: Indeed, it strongly proves, that, in chemistry, as in moral philosophy, it is extremely difficult to overcome prejudices imbibed in early education, and to search for truth in any other road than the one we have been accustomed to follow.

I shall finish this chapter by an experiment much less demonstrative than those already related, but which has appeared to make more impression than any other upon the minds of many people. When 16 ounces of alkohol are burnt in an apparatus[21] properly adapted for collecting all the water disengaged during the combustion, we obtain from 17 to 18 ounces of water. As no substance can furnish a product larger than its original bulk, it follows, that something else has united with the alkohol during its combustion; and I have already shown that this must be oxygen, or the base of air. Thus alkohol contains hydrogen, which is one of the elements of water; and the atmospheric air contains oxygen, which is the other element necessary to the composition of water. This experiment is a new proof that water is a compound substance.

FOOTNOTES:

[16] In the latter part of this work will be found a particular account of the processes necessary for separating the different kinds of ga.s.ses, and for determining their quant.i.ties.--A.

[17] This expression Hydrogen has been very severely criticised by some, who pretend that it signifies engendered by water, and not that which engenders water. The experiments related in this chapter prove, that, when water is decomposed, hydrogen is produced, and that, when hydrogen is combined with oxygen, water is produced: So that we may say, with equal truth, that water is produced from hydrogen, or hydrogen is produced from water.--A.

[18] See the nature of these salts in the second part of this book.--A.

[19] By potash is here meant, pure or caustic alkali, deprived of carbonic acid by means of quick-lime: In general, we may observe here, that all the alkalies and earths must invariably be considered as in their pure or caustic state, unless otherwise expressed.--E. The method of obtaining this pure alkali of potash will be given in the sequel.--A.

[20] See the third part of this work.--A.

[21] See an account of this apparatus in the third part of this work.--A.

CHAP. IX.

_Of the quant.i.ties of Caloric disengaged from different species of Combustion._

We have already mentioned, that, when any body is burnt in the center of a hollow sphere of ice and supplied with air at the temperature of zero (32), the quant.i.ty of ice melted from the inside of the sphere becomes a measure of the relative quant.i.ties of caloric disengaged. Mr de la Place and I gave a description of the apparatus employed for this kind of experiment in the Memoirs of the Academy for 1780, p. 355; and a description and plate of the same apparatus will be found in the third part of this work. With this apparatus, phosphorus, charcoal, and hydrogen gas, gave the following results:

One pound of phosphorus melted 100 libs. of ice.

One pound of charcoal melted 96 libs. 8 oz.

One pound of hydrogen gas melted 295 libs. 9 oz. 3-1/2 gros.

As a concrete acid is formed by the combustion of phosphorus, it is probable that very little caloric remains in the acid, and, consequently, that the above experiment gives us very nearly the whole quant.i.ty of caloric contained in the oxygen gas. Even if we suppose the phosphoric acid to contain a good deal of caloric, yet, as the phosphorus must have contained nearly an equal quant.i.ty before combustion, the error must be very small, as it will only consist of the difference between what was contained in the phosphorus before, and in the phosphoric acid after combustion.

I have already shown in Chap. V. that one pound of phosphorus absorbs one pound eight ounces of oxygen during combustion; and since, by the same operation, 100 lib. of ice are melted, it follows, that the quant.i.ty of caloric contained in one pound of oxygen gas is capable of melting 66 libs. 10 oz. 5 gros 24 grs. of ice.

One pound of charcoal during combustion melts only 96 libs. 8 oz. of ice, whilst it absorbs 2 libs. 9 oz. 1 gros 10 grs. of oxygen.

By the experiment with phosphorus, this quant.i.ty of oxygen gas ought to disengage a quant.i.ty of caloric sufficient to melt 171 libs. 6 oz. 5 gros of ice; consequently, during this experiment, a quant.i.ty of caloric, sufficient to melt 74 libs. 14 oz. 5 gros of ice disappears. Carbonic acid is not, like phosphoric acid, in a concrete state after combustion but in the state of gas, and requires to be united with caloric to enable it to subsist in that state; the quant.i.ty of caloric missing in the last experiment is evidently employed for that purpose. When we divide that quant.i.ty by the weight of carbonic acid, formed by the combustion of one pound of charcoal, we find that the quant.i.ty of caloric necessary for changing one pound of carbonic acid from the concrete to the ga.s.seous state, would be capable of melting 20 libs. 15 oz. 5 gros of ice.

We may make a similar calculation with the combustion of hydrogen gas and the consequent formation of water. During the combustion of one pound of hydrogen gas, 5 libs. 10 oz. 5 gros 24 grs. of oxygen gas are absorbed, and 295 libs. 9 oz. 3-1/2 gros of ice are melted. But 5 libs. 10 oz. 5 gros 24 grs. of oxygen gas, in changing from the aeriform to the solid state, loses, according to the experiment with phosphorus, enough of caloric to have melted 377 libs.

12 oz. 3 gros of ice. There is only disengaged, from the same quant.i.ty of oxygen, during its combustion with hydrogen gas, as much caloric as melts 295 libs. 2 oz. 3-1/2 gros; wherefore there remains in the water at Zero (32), formed, during this experiment, as much caloric as would melt 82 libs. 9 oz. 7-1/2 gros of ice.

Hence, as 6 libs. 10 oz. 5 gros 24 grs. of water are formed from the combustion of one pound of hydrogen gas with 5 libs. 10 oz. 5 gros 24 grs. of oxygen, it follows that, in each pound of water, at the temperature of Zero, (32), there exists as much caloric as would melt 12 libs. 5 oz. 2 gros 48 grs. of ice, without taking into account the quant.i.ty originally contained in the hydrogen gas, which we have been obliged to omit, for want of data to calculate its quant.i.ty.

From this it appears that water, even in the state of ice, contains a considerable quant.i.ty of caloric, and that oxygen, in entering into that combination, retains likewise a good proportion.

From these experiments, we may a.s.sume the following results as sufficiently established.

_Combustion of Phosphorus._

From the combustion of phosphorus, as related in the foregoing experiments, it appears, that one pound of phosphorus requires 1 lib.

8 oz. of oxygen gas for its combustion, and that 2 libs. 8 oz. of concrete phosphoric acid are produced.

The quant.i.ty of caloric disengaged by the combustion of one pound of phosphorus, expressed by the number of pounds of ice melted during that operation, is 100.00000.

The quant.i.ty disengaged from each pound of oxygen, during the combustion of phosphorus, expressed in the same manner, is 66.66667.

The quant.i.ty disengaged during the formation of one pound of phosphoric acid, 40.00000.

The quant.i.ty remaining in each pound of phosphoric acid, 0.00000(A).

[Note A: We here suppose the phosphoric acid not to contain any caloric, which is not strictly true; but, as I have before observed, the quant.i.ty it really contains is probably very small, and we have not given it a value, for want of a sufficient data to go upon.--A.]

_Combustion of Charcoal._

In the combustion of one pound of charcoal, 2 libs. 9 oz. 1 gros 10 grs. of oxygen gas are absorbed, and 3 libs. 9 oz. 1 gros 10 grs. of carbonic acid gas are formed.

Caloric, disengaged daring the combustion of one pound of charcoal, 96.50000(A).

Caloric disengaged during the combustion of charcoal, from each pound of oxygen gas absorbed, 37.52823.

Caloric disengaged during the formation of one pound of carbonic acid gas, 27.02024.

Caloric retained by each pound of oxygen after the combustion, 29.13844.

Caloric necessary for supporting one pound of carbonic acid in the state of gas, 20.97960.

[Note A: All these relative quant.i.ties of caloric are expressed by the number of pounds of ice, and decimal parts, melted during the several operations.--E.]

_Combustion of Hydrogen Gas._

In the combustion of one pound of hydrogen gas, 5 libs. 10 oz. 5 gros 24 grs. of oxygen gas are absorbed, and 6 libs. 10 oz. 5 gros 24 grs. of water are formed.

Caloric from each lib. of hydrogen gas, 295.58950.

Caloric from each lib. of oxygen gas, 52.16280.

Caloric disengaged during the formation of each pound of water, 44.33840.

Caloric retained by each lib. of oxygen after combustion with hydrogen, 14.50386.