Part 2

Before these experiments were attempted, I had analized nitrous gas and nitrous oxide, in a manner to be particularly described hereafter; so that a knowledge of the quantities of nitrous gas and oxygene entering into the composition of any acid, enabled me to determine the proportions of nitrogene and oxygene it contained. In consequence of which I attempted to combine together oxygene and nitrous gas, in such a manner as to absorb the nitrous acid formed by water, in an apparatus by which the quantities of the gases employed, and the increase of weight of the water, might be ascertained; but this process likewise failed. It was impossible to procure the gases perfectly free from nitrogene, and during their combination, this nitrogene made to pass into a pneumatic apparatus communicating with a vessel containing the water carried over with it, much nitrous acid vapor, of different composition from the acid absorbed.

After many unsuccessful trials, Dr. Priestley’s experiments on nitrous vapor[8] induced me to suppose that oxygene and nitrous gas, made to combine out of the contact of bodies having affinity for oxygene, would remain permanently aëriform, and on throwing them separately into an exhausted glass balloon, I found that this was actually the case; increase of temperature was produced, and orange colored nitrous acid gas formed, which after remaining for many days in the globe, at a temperature below 56°, did not in the slightest degree condense.

[8] Experiments and Observations, Vol. iii. last edition, page 105, &c.

This fact afforded me the means not only of forming a standard acid, but likewise of ascertaining the specific gravity of nitrous acid in its aëriform state.

III. Previous to the experiment, for the purpose of correcting incidental errors, I was induced to ascertain the specific gravity of the gases employed, particularly as I was unacquainted with any process by which the weight of nitrous gas had been accurately determined. Mr. Kirwan’s estimation, which is generally adopted, being founded upon the comparison of the loss of weight of a solution of copper in dilute nitrous acid, with the quantity of gas produced.[9]

The instruments that I made use of for containing and measuring my gases, were two mercurial airholders graduated to the cubic inch of Everard, and furnished with stop-cocks.[10]

[9] When copper is dissolved in dilute nitrous acid, certain quantities of nitrogene are generally produced, likewise the nitrous gas carries off in solution some nitrous acid.

[10] This airholder, considered as a pneumatic instrument, is of greater importance, and capable of a more extensive application than any other. It was invented by Mr. W. CLAYFIELD, and in its form is analogous to Mr. WATT’S hydraulic bellows, consisting of a glass bell playing under the pressure of the atmosphere, in a space between two cylinders filled with mercury. A particular account of it will be given in the appendix.

They were weighed in a glass globe, of the capacity of 108 cubic inches, which with the small glass stop-cock affixed to it, was equal, when filled with atmospheric air, to 1755 grains. The balance that I employed, when loaded with a pound, turned with less than one eighth of a grain.

Into a mercurial airholder, of the capacity of 200 cubic inches, 160 cubic inches of nitrous gas were thrown from a solution of mercury in nitrous acid.

70 measures of this were agitated for some minutes in a solution of sulphate of iron,[11] till the diminution was complete. The nitrogene remaining hardly filled a measure; and if we suppose with Humbolt[12] that a very small portion of it was absorbed with the nitrous gas, the whole quantity it contained may be estimated at 0,0142, or ¹/₇₀.

[11] This absorption will be hereafter particularly treated of.

[12] Annales de Chimie. Tome xviii. page 139.

75 cubic inches received from the airholder into an exhausted balloon, increased it in weight 25,5 grains; thermometer being 56°, and barometer 30,9. And allowing for the small quantity of nitrogene in the gas, 100 cubic inches of it will weigh 34.3 grains.

One hundred and thirty cubic inches of oxygene were procured from oxide of manganese and sulphuric acid, by heat, and received in another mercurial airholder.

10 measures of it, mingled with 26 of the nitrous gas, gave, after the residuum was exposed to solution of sulphate of iron, rather more than one measure. Hence we may conclude that it contained about 0,1 nitrogene.

60 cubic inches of it weighed 20,75 grains; and accounting for the nitrogene contained in these, 100 grains of pure oxygene will weigh 35,09 grains.

Atmospherical air was decomposed by nitrous gas in excess; and the residuum washed with solution of sulphate of iron till the Nitrogene remained pure; 87 cubic inches of it weighed 26,5 grains, thermometer being 48°, barometer 30,1; 100 will consequently weigh 30,45.

90 cubic inches of the air of the laboratory not deprived of its carbonic acid, weighed 28,75 grains; thermometer 53, barometer 30: 100 cubic inches will consequently weigh 31,9.[13] 16 measures of this air, with 16 nitrous gas, of known composition, diminished to 19. Hence it contained about,26 oxygene.[14]

In comparing my results with those of Lavoisier and Kirwan, the estimation of the weights of nitrogene and oxygene is very little different, the corrections for temperature and pressure being made, from that of those celebrated philosophers. The first makes oxygene to weigh[15] 34,21, and nitrogene 30,064 per cent; and the last, oxygene 34,[16] and nitrogene 30,5.

[13] A table of the specific gravities of these gases, and other gases, hereafter to be mentioned, reduced to a barometrical and thermometrical standard, will be given in the appendix.

[14] 40 measures, exposed to solution of potash, gave an absorption of not quite a quarter of a measure: hence it contained an inconsiderable quantity of carbonic acid.

[15] Traité Elementaire.

[16] Essai sur le phlogistique, page 30.

The specific gravity of nitrous gas, according to Kirwan, is to that of common air as 1194 to 1000. Hence it should weigh about 37 grains per cent. This difference from my estimation is not nearly so great as I expected to have found it.[17]

IV.[18] The thermometer in the laboratory standing at 55°, and the barometer at 30,1, I now proceeded to my experiment. The oxygene that I employed was of the same composition as that which I had previously weighed. The nitrous gas contained,0166 nitrogene.

For the purpose of combining the gases, a glass balloon was procured, of the capacity of 148 cubic inches, with a glass stop-cock adapted to it, having its upper orifice tubulated and graduated for the purpose of containing and measuring a fluid. The whole weight of this globe and its appendages, when filled with common air, was 2066,5 grains.

[17] The diminution of the specific gravity of the gas from the quantity of nitrogene evolved in his experiment, probably destroyed, in some measure, the source of error from the nitrous acid carried over.

[18] Experiment I.

It was partially exhausted by the air-pump, and lost in weight just 32 grains. From whence we may conclude that about 15 grains of air remained in it.

In this state of exhaustion it was immediately cemented to the stop-cock of the mercurial airholder, and the communication being made with great caution, 82 cubic inches of nitrous gas rushed into the globe, on the outside of which a slight increase of temperature was perceived, while the gases on the inside appeared of a deep orange.

Before the common temperature was restored, the communication was stopped, and the globe removed. The increase of weight was 29,25 grains; whence it appeared that 1,14 grains of common air, part of which had been contained in the stop-cocks, had entered with the nitrous gas.

Whilst it was cooling, from the accidental loosening of the stopper of the cock, 3 grains more of common air entered.[19]

[19] That no greater contraction took place depended on the solution of the nitrous acid formed in the nitrous gas; a phænomenon to be explained hereafter.

The communication was now made between the globe and the mercurial airholder containing oxygene. 64 cubic inches were slowly pressed in, when the outside of the globe became warmer, and the color on the inside changed to a very dark orange. As it cooled, 6 cubic inches more slowly entered; but no new increase of temperature, or change of color took place.

The globe being now completely cold, was stopped, removed, and weighed; it had gained 24,5 grains, from whence it appears that 0,4 grains of common air contained in the stop-cocks, had entered with the oxygene.[20]

[20] I judged it expedient always to ascertain the quantity of air in the stop-cocks by weight, as it was impossible to join them so as to have always an equal capacity. The upper tubes of the two stop-cocks not joined, contained nearly an inch and half.

To absorb the nitrous acid gas, 41 grains of water were introduced by the tube of the stop-cock, which though closed as rapidly as possible, must have suffered nearly,5 grains of air to enter at the same time, as the increase of weight was 41,5 grains. The dark orange of the globe diminished rapidly; it became warm at the bottom, and moist on the sides. After a few minutes the color had almost wholly disappeared.

To ascertain the quantity of aëriform fluid absorbed, the globe was again attached to the mercurial air apparatus, containing 140 cubic inches of common air. When the communication was made, 51 cubic inches rushed in, and it gained in weight 16,5 grains.

A quantity of fluid equal to 54 grains was now taken out of the globe. On examination it proved to be slightly tinged with green, and occupied a space equal to that filled by 41,5 grains of water. Its specific gravity was consequently 1,301.

To ascertain if any unabsorbed aëriform nitrous acid remained in the globe, 13 grains of solution of ammonia were introduced in the same manner as the water, and after some minutes, when the white vapor had condensed, the communication was again made with the mercurial airholder containing common air. A minute quantity entered, which could not be estimated at more than three fourths of an inch, and the globe was increased in weight about 13,25 grains.[21]

Common air was now thrown into the globe till the residual gases of the experiment were judged to be displaced; it weighed 2106,5 grains, that is, 40 grains more than it had weighed when filled with common air before the experiment.[22]

[21] That is, by the solution of ammonia, and air.

[22] The following is an account of the increase and diminution of weight of the globe, as it was noted in the journal.

Globe filled with common air gr. 2066,5 After exhaustion 2034,5 After introduction of nitrous gas, 82 cubic inches 2064,25 After the accidental admission of common air 2067,25 After the admission of oxygene 2091,75 —— —— 41 grains of water 2133,25 —— —— 51 cubic inches of air 2149,75 Taken out 54 grains of solution 2095,75 Introduced 13 grains of ammoniacal solution 2109,25 After introduction of common air 2106,5

And if from those 40 grains we take 13 for the solution of ammonia introduced, the remainder, 27, will be the quantity of solution of nitrous acid in water remaining in the globe, which added to 54, equals 81 grains, the whole quantity formed; but if from this be taken 41 grains, the quantity of water, the remainder 40 grains, will be the quantity of nitrous acid gas absorbed in the solution.

To find the absolute quantity of nitrous acid formed, we must find the specific gravity of that absorbed; but as during, and after its absorption, 17 grains of air, equal to 53,2 cubic inches entered, it evidently filled such a space. 53,2 cubic inches of it consequently weigh 40 grains, and 100 cubic inches 75,17 grains. Then,75 cubic inches weigh,56 grains, and this added to 40, makes 40,56 grains, equal to 53,95 cubic inches, the whole quantity of aëriform nitrous acid produced.

But the quantity of nitrous gas entering into this, allowing for the nitrogene it contained, is 27,6 grains, equal to about 80,5 cubic inches; and the oxygene is 40,56-27,6 = to 12,96 grains, or 36,9 cubic inches.

V. There could exist in this experiment no circumstance connected with inaccuracy, except the impossibility of very minutely determining the quantities of common air which entered with the gases from the stop-cocks. But if errors have arisen from this source, they must be very inconsiderable; as will appear from a calculation of the specific gravity of the nitrous acid gas, founded on the volume of the gases that entered the globe.

The air that remained in the globe after exhaustion was 15 grains = 47[23] cub. in. The nitrous gas introduced was 82 Common air 13 Oxygene 70 Common air 1 —— Whole quantity of air thrown into the globe 213 From which subtract its capacity 148 —— The remainder is 65

[23] Decimals are omitted, because the excess of the two first numbers is exactly corrected by the deficiency of the last.

And this remainder taken from 80,5 nitrous gas + 36,9 oxygene, leaves 52,4 cubic inches, which is the space occupied by the nitrous acid gas, and which differs from 53,95 only by 1,55 cubic inches.

I ought to have observed, that before this conclusive experiment, two similar ones had been made. In comparing the results of one of them, performed with the assistance of my friend, Mr. JOSEPH PRIESTLEY, Dr. PRIESTLEY’S eldest son, and chiefly detailed by him in the journal, I find a coincidence greater than could be even well expected, where the processes are so complex. According to that experiment, 41,5 grains of nitrous acid gas fill a space equal to 53 cubic inches, and are composed of nearly 29 nitrous gas, and 12,5 oxygene.

We may then conclude, First, that 100 cubic inches of nitrous acid, such as exists in the[24] aëriform state saturated with oxygene, at temperature 55°, and atmospheric pressure 30,1 weigh 75,17 grains.

[24] As is evident from the superabundant quantity of oxygene thrown into the globe.

Secondly, that 100 grains of it are composed of 68,06 nitrous gas, and 31,94 oxygene. Or assuming what will be hereafter proved, that 100 parts of nitrous gas consist of 55,95 oxygene, and 44,05 nitrogene, of 29,9 nitrogene, and 70,1 oxygene; or taking away decimals, of 30 of the one to 70 of the other.

Thirdly, that 100 grains of pale green solution of nitrous acid in water, of specific gravity 1,301, are composed of 50,62 water, and 49,38 acid of the above composition.

VI. Having thus ascertained the composition of a standard acid, my next object was to obtain it in a more condensed state, as it was otherwise impossible to saturate it to its full extent with nitrous gas. But this I could effect in no other way than by comparing mixtures of known quantities of water, and acids of different specific gravities and colors, with the acid of 1,301.

For the purpose of combining my acids with water, I made use of a cylinder about 8 inches long, and,3 inches in diameter, accurately graduated to grain measures, and furnished with a very tight stopper.

The concentrated acid was first slowly poured into it, and the water gradually added till the required specific gravity was produced;[25] the cylinder being closed and agitated after each addition, so as to produce combination without any liberation of elastic fluid.

[25] The weight of the acid poured into the cylinder being known, its specific gravity was known from the space it occupied in the phial. The weight of water being likewise known, the specific gravity of the solution, when the common temperature was produced, was given by the condensation.

After making a number of experiments with acids of different colors in this advantageous way, I at length found that 90 grains of a deep yellow acid, of specific gravity 1,5, became, when mingled at 40° with 77,5 grains of water, of specific gravity 1,302, and of a light green tinge, as nearly as possible resembling that of the standard acid.

Supposing, then, that these acids contain nearly the same relative proportions of oxygene and nitrogene, 100 grains of the deep yellow acid of 1,5, are composed of 91,9 grains true nitrous acid,[26] and 8,1 grains of water.

[26] That is, such as it exists in the aëriform state at 55°. From the strong affinity of nitrous acid for water, we may suppose that this acid gas contains a larger proportion of it than the other gases.

To ascertain the difference between the composition of this acid, and that of the pale, or nitric acid, of the same specific gravity, I inserted 150 grains of it into a small cylindrical mattrass of the capacity of,5 cubic inches, accurately graduated to grain measures, and connected by a curved tube with the water apparatus. After heat had been applied to the bottom of the mattrass for a few minutes, the color of the fluid gradually changed to a deep red, whilst the globules of gas formed at the bottom of the acid, were almost wholly absorbed in passing through it. In a short time deep red vapour began to fill the tube, and being condensed by the water in the apparatus, was converted into a bright green fluid, at the same time that minute globules of gas were given out. As the heat applied became more intense, a very singular phænomenon presented itself; the condensed vapor, increased in quantity, at length filled the curvature of the tube, and when expelled, formed itself into dark green spherules, which sunk to the bottom of the water, rested for a moment, and then resolved themselves into nitrous gas.[27]

[27] This appearance will be explained hereafter.

When the acid was become completely pale, it was suffered to cool, and weighed. It had lost near 15 grains, and was of specific gravity 1,491. 2 cubic inches and quarter of nitrous gas only were collected.

From this experiment evidently no conclusions could be drawn, as the nitrous gas had carried over with it much nitrous acid (in the form of what Dr. Priestley calls nitrous vapor) and was partially dissolved with it in the water.[28]

[28] This phænomenon will be particularly explained hereafter.

To ascertain, then, the difference between the pale and yellow acids, I was obliged to make use of synthesis, compared with analysis, carried on in a different mode, by means of the following apparatus.

VII. To the stop-cock of the upper cylinder of the mercurial airholder, a capillary tube was adapted, bent so as to be capable of introduction into an orifice in the stopper of a graduated phial similar to that employed for mingling acids with water, and sufficiently long to reach the bottom. With another orifice in the stopper of the phial was connected a similar tube curved, for the purpose of containing a fluid, and of increased diameter at the extremity.[29]

50 cubic inches of pure nitrous gas[30] were thrown into the mercurial apparatus. The graduated phial, containing 90 grains of nitric acid, of specific gravity 1,5, was placed on the top of the airholding cylinder, and made to communicate with it by means of the stop-cock and first tube. Into the second tube a small quantity of solution of potash was placed. When all the junctures were carefully cemented, by pressing on the airholder, the nitrous gas was slowly passed into the phial, and absorbed by the nitrous acid it contained; whilst the small quantities of nitrogene evolved, slowly drove forward the solution in the curved tube; from the height of which, as compared with that of the mercury in the conducing tube, the pressure on the air in the cylinder was known.

In proportion as the nitrous gas was absorbed, the phial became warm, and the acid changed color; it first became straw-colored, then pale yellow, and when about 7½ cubic inches had been combined with it, bright yellow. It had gained in weight nearly 3 grains, and was become of specific gravity 1,496.

[29] The outline only of this apparatus is given here, as far as was necessary to make the experiment intelligible; a detailed account of it, and of its general application, will be given in the appendix.

[30] That is, from nitrous acid and mercury.

This experiment afforded me an approximation to the real difference between nitric and yellow nitrous acid; and learning from it that nitric acid was diminished in specific gravity by combination with nitrous gas, I procured a pale acid of specific gravity 1,504.[31] After this acid had been combined in the same manner as before, with about 8 cubic inches of nitrous gas,[32] it became nearly of specific gravity 1,5, and had gained in weight about 3 grains.

[31] A pale acid of 1.52, by being converted into yellow acid, became nearly of specific gravity 15,1.

[32] It is impossible to ascertain the quantity of gas absorbed to more than a quarter of a cubic inch, as the first portions of nitrous gas thrown into the graduated cylinder are combined with the oxygene of the common air in it, to form nitrous acid, and hence the slight excess of weight.

Assuming the accuracy of this experiment as a foundation for calculation, I endeavoured in the same manner to ascertain the differences in the composition of the orange colored acids, and the acids containing still larger proportions of nitrous gas.

93 grains of the bright yellow acid of 1,5 became, when 6 cubic inches of gas had been passed through it, orange colored and fuming, whilst the undissolved gas increased in quantity so much as to render it impossible to confine it by the solution of potash. When 9 cubic inches had passed through, it became dark orange. It had gained in weight 2,75 grains, and was become of specific gravity 1,48 nearly. Hence it was evident that much nitrous gas had passed through it undissolved. 25 cubic inches more of nitrous gas were now slowly sent through it: it first became of a light olive, then of a dark olive, then of a muddy green, then of a bright green, and lastly of a blue green. After its assumption of this color, the gas appeared to pass through it unaltered, and large globules of fluid, of a darker green than the rest, remained at the bottom of the cylinder, and when agitated, did not combine with it. The increase of weight was only 1 grain, and the acid was of specific gravity 1,474 nearly.

In this experiment it was evident that the unabsorbed nitrous gas had carried over with it a considerable quantity of nitrous acid. I endeavoured to correct the errors resulting from this circumstance, by connecting the curved tube first with a small water apparatus, and afterwards with a mercurial apparatus; but when the water apparatus was used, the greater part of the unabsorbed gas was dissolved with the nitrous acid it held in solution, by the water; and when mercury was employed, the nitrous acid that came over was decomposed, and the quantity of nitrous gas evolved, in consequence increased.

As it was possible that a small deficiency of weight might arise from the red vapor given out during the processes of weighing and examining the acid in the last experiment, 35 cubic inches of nitrous gas were very slowly passed through 90 grains of pale nitrous acid, of specific gravity 1,5: it became of similar appearance to that just described, had gained in weight 6,75 grains, and was become of specific gravity 1,475.