William Prout (1785-1850)

On the Relation between the Specific Gravities of Bodies in their Gaseous State and the Weights of their Atoms.

The author of the following essay submits it to the public with the greatest diffidence; for though he has taken the utmost pains to arrive at the truth, yet he has not that confidence in his abilities as an experimentalist as to induce him to dictate to others far superior that its importance will be seen, and that some one will undertake to examine it, and thus verify or refute its conclusions. If these should be proved erroneous, still new facts may be brought to light, or old ones better established, by the investigation; but if they should be verified, a new and interesting light will be thrown upon the whole science of chemistry.

It will perhaps be necessary to premise that the observations about to be offered are chiefly founded on the doctrine of volumes as first generalized by M. Gay-Lussac; and which, as far as the author is aware at least, is now universally admitted by chemists.

On the Specific Gravities of the Elementary Gases.

Hence, then, it must be considered in the light of a pure chemical compound; and indeed nothing but this supposition will account for its uniformity all over the world, as demonstrated by numerous experiments. From these data the specific gravities of oxygen and azote (atmospheric air being 1.000) will be found to be,[1]

Oxygen	1.1111
Azote	.9722

2. Hydrogen.-- The specific gravity of hydrogen, on account of its great levity, and the obstinacy with which it retains water, has always been considered as the most difficult to take of any other gas. These obstacles made me (to speak in the first person) despair of arriving at a more just conclusion than had been before obtained by the usual process of weighing; and it occurred to me that its specific gravity might be much more accurately obtained by calculation from the specific gravity of a denser compound into which it entered in a known proportion. Ammoniacal gas appeared to be the best suited to my purpose, as its specific gravity has been taken with great care by Sir H. Davy, and the chance of error had been much diminished from the slight difference between its sp. gr. and that of steam. Moreover, Biot and Arrago had obtained almost precisely the same result as Sir H. Davy. The sp. gr. of ammonia, according to sir H. Davy, is .590164, atmospheric air being 1.000. We shall consider it as .5902; and this we are authorized in doing, as Biot and Arrago state it somewhat higher than Sir H. Davy. Now ammonia consists of three volumes of hydrogen and one volume of azote condensed into two volumes. Hence the sp. gr. of hydrogen will be found to be .0694,[2] atmospheric air being 1.0000. It will be also observed that the sp. gr. of oxygen as obtained above is just 16 times that of hydrogen as now ascertained, and the sp. gr. of azote just 14 times.[3]

3. Chlorine. The specific gravity of muriatic acid, according to Sir H. Davy's experiments, which coincide exactly with those of Biot and Arrago, is 1.278. Now if we suppose this sp. gr. to be erroneous in the same proportion that we found the sp. gr. of oxygen and azote to be above, (which, though not rigidly accurate, may yet be fairly done, since the experiments were conducted in a similar manner), the sp. gr. of this gas will come out about 1.2845;[4] and since it is a compound of one volume chlorine and one volume hydrogen, the specific gravity of chlorine will be found by calculation to be 2.5.[5] Dr. Thomson states, that he has found 2.483 to be near the truth,[6] and Gay-Lussac almost coincides with him.[7] Hence there is every reason for concluding that the sp. gr. of chlorine does not differ much from 2.5. On this supposition, the sp. gr. of chlorine will be found exactly 36 times that of hydrogen.

On the Specific Gravities of Elementary Substances in a Gaseous State that do not at ordinary Temperatures exist in that State.

2. Carbon. I assume the weight of an atom of carbon at 7.5. Hence the sp. gr. of a volume of it in a state of gas will be found by calculation to be .4166, or exactly 12 times that of hydrogen.

3. Sulphur.-- The weight of an atom of sulphur is 20. Hence the specific gravity of its gas is the same as that of oxygen, or 1.1111, and consequently just 16 times that of hydrogen.

4. Phosphorus.-- I have made many experiments in order to ascertain the weight of an atom of this substance; but, after all, have not been able to satisfy myself, and want of leisure will not permit me to pursue the subject further at present. The results I have obtained approached nearly to those given by Dr. Wollaston, which I am therefore satisfied are correct, or nearly so, and which fix phosphorus at about 17.5, and phosphoric acid at 37.5,[10] and these numbers at present I adopt.

5. Calcium.-- Dr. Marcet found carbonate of lime composed of 43.9 carbonic acid and 56.1 lime.[11] Hence as 43.9:56.1::27.5:35.1, or 35 very nearly; and 35 - 10 = 25, for the atom of calcium. The sp. gr. of a volume of its gas will therefore be 1.3888, or exactly 20 times that of hydrogen.

6. Sodium.-- 100 grains of dilute muriatic acid dissolved 18.6 grs. of carbonate of lime, and the same quantity of the same dilute acid dissolved only 8.2 grs. of carbonate of lime, after there had been previously added 30 grs. of a very pure crystallized subcarbonate of soda. Hence 30 grs. of crystallized subcarbonate of soda are equivalent to 10.4 grs. of carbonate of lime, and as 10.4:30::62.5:180. Now 100 grs. of crystallized subcarbonate of soda were found by application of heat to lose 62.5 of water. Hence 180 grs. of the same salt contain 112.5 of water, equal to 10 atoms, and 67.5 dry subcarbonate of soda, and 67.5 - 27.5 = 40 for the atom of soda, and 40 - 10 = 30 for the atom of sodium. Hence a volume of it in a gaseous state will weigh 1.6666, or exactly 24 times that of hydrogen.

7. Iron.-- 100 grs. of dilute muriatic acid dissolved as before 18.6 grs. of carbonate of lime, and the same quantity of the same acid dissolved 10.45 of iron. Hence as 18.6:10.45::62.5:35.1, or for the sake of analogy, 35, the weight of an atom of iron. The sp. gr. of a volume of this metal in a gaseous state will be 1.9444, or exactly 28 times that of hydrogen.

8. Zinc.-- 100 grs. of the same dilute acid dissolved, as before, 18.6 of carbonate of lime and 11.85 of zinc. Hence as 18.6:11.85::62.5:39.82, the weight of the atom of zinc, considered from analogy to be 40. Hence the sp. gr. of a volume of it in a gaseous state will be 2.222, or exactly 32 times that of hydrogen.

9. Potassium.-- 100 grs. of the same dilute acid dissolved, as before, 18.6 carbonate of lime; but after the addition of 20 grs. of super-carbonate of potash, only 8.7 carbonate of lime. Hence 20 grs. of super-carbonate of potash are equivalent to 9.9 carbonate of lime; and as 9.9:20::62.5:126.26, the weight of the atom of super-carbonate of potash. Now 126.26 - (55 + 11.25) = 60, the weight of the atom of potash, and 60 - 10 = 50, the weight of the atom of potassium. Hence a volume of it in a state of gas will weigh 2.7777, or exactly 40 times as much as hydrogen.

10. Barytium.-- 100 grs. of the same dilute acid dissolved exactly as much again of carbonate of barytes as of carbonate of lime. Hence the weight of the atom of carbonate of barytes is 125; and 125 - 27.5 = 97.5, the weight of the atom of barytium. The sp. gr. therefore, of a volume of its gas will be 4.8611, or exactly 70 times that of hydrogen.

With respect to the above experiments, I may add, that they were made with the greatest possible attention to accuracy, and most of them were many times repeated with almost precisely the same results.

The following tables exhibit a general view of the above results, and at the same time the proportions, both in volume and weight, in which they unite with oxygen and hydrogen: also the weights of other substances, which have not been rigidly examined, are here stated from analogy.

TABLE I.-- Elementary Substances.

TABLE II.-- Combinations with Oxygen.

TABLE III.-- Compounds with Hydrogen.

TABLE IV.-- Substances stated from Analogy, but of which we are yet uncertain.

Observations.

Table II.-- This table exhibits many striking instances of the near coincidence of theory and experiment. It will be seen that Gay-Lussac's views are adopted, or rather indeed anticipated, as a good deal of this table was drawn up before I had an opportunity of seeing the latter part of that chemist's memoir on iodine. That table also exhibits one or two striking examples of the errors that have arisen from not clearly understanding the relation between the doctrine of volumes and of atoms. Thus ammonia has been stated to be composed of one atom of azote and only 1.5 of hydrogen, which are condensed into two volumes, equal therefore to one atom; and this is the reason why this substance, like some others, apparently combine in double proportions.[12]

Table III.-- This table likewise exhibits some striking examples of the coincidences above noticed. Indeed, I had often observed the near approach to round numbers of many of the weights of the atoms, before I was led to investigate the subject. Dr. Thomson appears also to have made the same remark. It is also worthy of observation, that the three magnetic metals, as noticed by Dr. Thomson, have the same weight, which is exactly double that of azote. Substances in general of the same weight appear to combine readily, and somewhat resemble one another in their nature.

On a general review of the tables, we may notice,
1. That all the elementary numbers, hydrogen being considered as 1, are divisible by 4, except carbon, azote, and barytium, and these are divisible by 2, appearing therefore to indicate that they are modified by a higher number than that of unity or hydrogen. Is the other number 16, or oxygen? And are all substances compounded of these two elements?
2. That oxygen does not appear to enter into a compound in the ratio of two volumes or four atoms.
3. That all the gases, after having been dried as much as possible, still contain water, the quantity of which, supposing the present views are correct, may be ascertained with the greatest accuracy.

Others might doubtless be mentioned; but I submit the matter for the present to the consideration of the chemical world.

[Notes: --CJG]

[2]Let x = sp. gr. of hydrogen.
Then (3x+.9722)/2 = .5902.
Hence x = (1.1804-.9722)/3 = .0694.

[3]1.11111 / .0694 = 16. And .9722 / .0694 = 14.

[4]As 1.104:1.11111::1.278:1.286.
And as .969:.9722::1.278:1.283. The mean of these is 1.2845.

[5]Let x = sp. gr. of chlorine.
Then (x+.0694)/2 = 1.2845.
And x = 2.569-.0694 = 2.5 very nearly.

[6]Annals of Philosophy, vol. iv. p. 13.

[7]Ditto, vol. vi. p. 126.

[8]As 25.8:100::40:155. According to experiment 8th, stated below, the weight of an atom of zinc is 40. Dr. Thomson makes it 40.9, which differs very little. See Annals of Philosophy, vol. iv. p. 94.

[9]One volume of hydrogen combines with only half a volume of oxygen, but with a whole volume of gaseous iodine, according to M. Gay-Lussac. The ratio in volume, therefore, between oxygen and iodine is as 1/2 to 1, and the ratio in weight is as 1 to 15.5. Now .5555, the density of half a volume of oxygen, multiplied by 15.5, gives 8.61111, and 8.61111 / .06944 = 124. Or generally, to find the sp. gr. of any substance in a state of gas, we have only to multiply half the sp. gr. of oxygen by the weight of the atom of the substances with respect to oxygen. See Annals of Philosophy, vol. v. p. 105.

[10]Some of my experiments approached nearer to 20 phosphorus and 40 phosphoric acid.

[11]I quote on the authority of Dr. Thomson, Annals of Philosophy, vol. iii, p. 376. Dr. Wollaston makes it somewhat different, or that carbonate of lime consists of 43.7 acid and 56.3 lime. Phil. Trans. vol. civ. p. 8.

[12]See Gay-Lussac's memoir on iodine, Annals of Philosophy, vi. 189.

Correction of a Mistake in the Essay on the Relation between the Specific Gravities of Bodies in their Gaseous State and the Weights of their Atoms

The author of the essay On the Relation between the Specific Gravities of Bodies in their Gaseous State and the Weights of their Atoms is anxious to correct an oversight which influences some of the numbers in the third table given in that essay (vol. vi. p. 328). This oversight will be found in the head or title of the third column in each table, and consists in the statement of the atom of hydrogen being composed of two volumes instead of one, upon which latter supposition the tables are actually constructed, except in the instances corrected in the third table as follows, and in a sentence in the first paragraph on p. 330, beginning "This table also exhibits," &c. which is to be expunged.

Name.	Sp. gr. hydro. being 1	Wt. of atom, hydrogen being 1.	Wt. of atom, oxygen being 10.	Wt. of atom, oxygen being 10, from experiment.	Sp. gr. atmospheric air being 1.	Sp. gr. atmospheric air being 1, from experiment.	Wt. of 100 cub. inch. Bar. 30. Ther. 60.	Wt. of 100 cub. inch. from exper.	Elements by volume.	No. of vol. after condensation.	Elements by weight.	Observations.
Carburetted hydrogen	8	4	5	5.09	.5555	.5555(1)	16.999	16.999	1 hyd + .5 car	.5	1 hyd + .5 car	(1)Dr. Thomson.
Olefiant gas	14	7	8.75	8.86	.9722	.9740(1)	29.652	29.72	1 hyd + 1 car	.5	1 hyd + 1 car
Sulphureted hydrogen	17	17	21.25	21.32	1.1805	1.177	36.006	35.89	1 hyd + 1 sul	1	1 hyd + 1 sul
Muriatic acid	18.5	37	46.25	45.42	1.284	1.278	39.183	38.979	1 hyd + 1 chl	2	1 hyd + 1 chl
Hydriodic acid	62.5	125	156.25	157.53	4.3402	4.3463(2)	132.375	--	1 hyd + 1 iod	2	1 hyd + 1 iod	(2)Gay-Lussac.
Ammonia	8.5	17	21.25	21.5(3)	.5902(4)	.5900	18.003	18.000	3 hyd + 1 az	2	3 hyd + 1 az	(3)Dr. Wollaston. (4)Sir H. Davy.
Cyanogen	26	26	32.5	32.52	1.8055	1.8064(5)	55.068	--	2 car + 1 az	1	2 car + 1 az	(5)Gay-Lussac. Ann. de Chim. Aug. 1815.
Hydro-cyanic acid	13.5	27	33.75	33.846	.9374	.9360(5)	28.593	--	1 cya + 1 hy	2	1 cya + 1 az
Chloro-cyanic acid	31	62	77.5	--	2.1527	2.1111(5)	65.659	--	1 cya + 1 chl	2	1 cya + 1 chl

In this table it will be also observed that the new determinations of Gay-Lussac respecting the prussic acid, &c. are inserted, to show that they correspond with, and further corroborate, the views which have been brought forward in the essay above referred to.

There is an advantage in considering the volume of hydrogen equal to the atom, as in this case the specific gravities of most, or perhaps all, elementary substances (hydrogen being 1) will either exactly coincide with, or be some multiple of, the weights of their atoms; whereas if we make the volume of oxygen unity, the weights of the atoms of most elementary substances, except oxygen, will be double that of the specific gravities of bodies in their gaseous state (either with respect to hydrogen or atmospheric air), by means of Dr. Wollaston's logometric scale.

If the view we have ventured to advance be correct, we may almost consider the πρωτη υλη of the ancients to be realised in hydrogen; an opinion, by the by, not altogether new. If we actually consider this to be the case, and further consider the specific gravities of bodies in their gaseous state to represent the number of volumes condensed into one; or, in other words, the number of the absolute weight of a single volume of the first matter (πρωτη υλη) which they contain, which is extremely probable, multiples in weight must always indicate multiples in volume, and vice versa; and the specific gravities, or absolute weights of all bodies in a gaseous state, must be multiples of the specific gravity or absolute weight of the first matter (πρωτη υλη), because all bodies in a gaseous state which unite with one another unite with reference to their volume.