Part 6
After the process was finished, the communication between the mercurial airholder and the recipient was preserved till the common temperature was restored to the retort.
The volume of the gas in the cylinder was 85,5 cubic inches. The absolute quantity of nitrous oxide in those 85,5 cubic inches, it was difficult to ascertain with great nicety, on account of the common air previously contained in the vessels.
45 measures of it, exposed to well boiled water, diminished by agitation to 8 measures. So that reasoning from the quantity of air, which should have been expelled from the water by the nitrous oxide, we may conclude that the 85,5 cubic inches were nearly pure.
The retort now weighed 419,25 grains, consequently 5,5 grains of salt remained in it. This salt was chiefly collected about the lower part of the neck, and contained rather more water than the compact nitrate, as in some places it was crystalised.
The recipient with the fluid it contained, weighed 759 grains. It had consequently gained in weight 48 grains.
Now the 85,5 cubic inches of nitrous oxide produced, weigh about 42,5 grains; and this added to 48 and 5,5, = 96 grains; so that about 4 grains of salt and fluid were lost, probably by being carried over and deposited by the gas.[86]
[86] This was actually the case; for on examining the conducting tube the day after the experiment, some minute crystals of prismatic nitrate of ammoniac were perceived in it.
As much of the fluid as could be taken out of the recipient, weighed 46 grains, and held in solution much nitrate of ammoniac with superabundance of acid. This acid required for its saturation, 3⅛ of carbonate of ammoniac (containing, as well as I could guess), about 20 per cent alkali.
The whole solution evaporated, gave 18 grains of compact nitrate of ammoniac. But reasoning from the quantity of carbonate of ammoniac employed, the free nitric acid was equal to 2,75 grains, and this must have formed 3,56 grains of salt. Consequently the salt pre-existing in the solution was about 14,44 grains.
But besides the fluid taken out of the recipient, 2 grains remained in it: let us suppose this, and the 4 grains lost, to contain 2 of salt, and,6 of free acid.
Then the undecompounded
salt is 5,5 + 14,4 + 2 = 21,9 The free acid 2,75 + ,6 = 3,35 Gas 42,5 Water 32,25 —————— 100
Now about 78,1 grains of salt were decompounded, and formed into 42,5 grains of gas, 3,35 grains acid, and 32,25 grains water.
But there is every reason to suppose, that in this process, when the hydrogene of the ammoniac combines with a portion of the oxygene of the nitric acid to form water, and the nitrogene enters into union with the nitrogene and remaining oxygene of the nitric acid, to form nitrous oxide; that water pre-existing in nitric acid and ammoniac, such as they existed in the aëriform state, is deposited with the water produced by the new arrangement, and not wholly combined with the nitrous oxide formed. Hence it is impossible to determine with great exactness, the quantity of water which was absolutely formed in this experiment.
78,1 grains of salt are composed of 15,4 alkali, 58 acid, and 4,7 water.
And reasoning from the different affinities of water for nitric acid, ammoniac, and nitrous oxide, it is probable that ammoniac, in its decomposition, divides its water in such a ratio, between the nitrogene furnished to the nitrous oxide, and the hydrogene entering into union with the oxygene of the nitric acid, as to enable us to assume, that the hydrogene requires for its saturation nearly the same quantity of oxygene as when in the aëriform state; or that it certainly cannot require less.
But 15,4 alkali contain 3,08 hydrogene, and 12,32 nitrogene;[87] and 3,08 hydrogene require 17,4 of oxygene to form 20,48 of water.
[87] Owing part of their weight to an unknown quantity of water.
Now 32,5 grains of water existed before the experiment; 4,7 grains of water were contained by the salt decomposed, and 32,5-4,7 = 27,8: and 27,8-20,48, the quantity generated, = 7,52, the quantity existing in the nitric acid.
But the nitric acid decomposed is 58ᵍ-3,35 = to 54,7; and 54,7-7,5 = 47,2, which entered into new combinations. These 47,2 consist of 33,2 oxygene, and 14, nitrogene. And 33,2-17,4, the quantity employed to form the water, = 15,8, which combined with 14,0, nitrogene of the nitric acid, and 12,32 of that of the ammoniac, to form 42,12 of nitrous oxide. And on this estimation, 100 parts of nitrous oxide would contain 37,6 oxygene, and 62,4 nitrogene; a computation much nearer the results of the analysis than could have been expected, particularly as so many unavoidable sources of error existed in the process.
The experiment that I have detailed is the most accurate of four, made on the same quantity of salt. The others were carried on at rather higher temperatures, in consequence of which, more water and salt were sublimed with the gas.
To Berthollet, we owe the discovery of the products evolved during the slow decomposition of nitrate of ammoniac; but as this philosopher in his examination of this process, chiefly designed to prove the existence of hydrogene in ammoniac, he did not ascertain the quantity of gas produced, or minutely examine its properties; from two of them, its absorption by water and its capability of supporting the vivid combustion of a taper, he inferred its identity with the dephlogisticated nitrous gas of Priestley, and concluded that it was nitrous gas with excess of pure air.[88]
[88] Mem. de Paris. 1785, and Journal de Physique, 1786, page 175.
VII. _Of the heat produced during the decomposition of nitrate of ammoniac._
To ascertain whether the temperature of nitrate of ammoniac was increased or diminished after it had been raised to the point essential to its decomposition, during the evolution of nitrous oxide and water; that is, in common language, whether heat was generated or absorbed in the process; I introduced a thermometer into about 1500 grains of fibrous nitrate of ammoniac, rendered liquid in a deep porcelain cup. During the whole of the evaporation, the temperature was about 380°, the fire being carefully regulated.
As soon as the decomposition took place, the thermometer began to rise; in less than a quarter of a minute it was 410°, in two minutes it was 460°.
The cup was removed from the fire; the decomposition still went on rapidly, and for about a minute the thermometer was stationary. It then gradually and slowly fell; in three minutes it was 440°, in five minutes 420°, in seven minutes 405° in nine minutes 360° and in thirteen minutes 307°, when the decomposition had nearly ceased, and the salt began to solidify.
From this experiment, it is evident that an increase of temperature is produced by the decomposition of nitrate of ammoniac: though the capacity of water and nitrous oxide for heat, supposing the truth of the common doctrine, and reasoning from analogy, must be considerably greater than that of the salt.
VIII. _Of the decomposition of Nitrate of Ammoniac at high temperatures, and production of Nitrous gas, Nitrogene, Nitrous Acid, and Water._
At an early period of my investigation relating to the nitrous oxide, I discovered that when a heat above 600° was applied to nitrate of ammoniac, so that a vivid luminous appearance was produced in the retort, certain portions of nitrous gas, and nitrogene, were evolved with the nitrous oxide. But I was for some time ignorant of the precise nature of this decomposition, and doubtful with regard to the possibility of effecting it in such a manner as to prevent the production of nitrous oxide altogether.
I first attempted to decompose nitrate of ammoniac at high temperatures, by introducing it into a well coated green glass retort, having a wide neck, communicating with the pneumatic apparatus, and strongly heated in an air-furnace. But though in this process a detonation always took place, and much light was produced, yet still the greater portion of the gas generated was nitrous oxide; the nitrous gas and nitrogene never amounting to more than one third of the whole.
After breaking many retorts by explosions, without gaining any accurate results, I employed a porcelain tube, curved so as to be capable of introduction into the pneumatic apparatus, and closed at one end.
The closed end was heated red, nitrate of ammoniac introduced into it, and all the latter portions of gas produced in the explosion, received in the pneumatic apparatus, filled with warm water.
Three explosions were required to fill a jar of the capacity of 20 cubic inches. The gas produced in the first, when it came over, was transparent and dark orange, similar in its appearance to the nitrous acid gas produced in the first experiment; but it speedily became white and clouded, whilst a slight diminution of volume took place.
When the second portion was generated and mingled with the clouded gas, it again became transparent and yellow for a short time, and then assumed the same appearance as before.
The water in the trough, after this experiment, had an acid taste, and quickly reddened cabbage juice rendered green by an alkali.
6 cubic inches of the gas produced were exposed to boiled water, but little or no absorption took place. Hence, evidently, it contained no nitrous oxide.
They were then exposed to solution of sulphate of iron: the solution quickly became dark colored, and an absorption of 1,6 took place on agitation.[89]
[89] The absorption of nitrous gas by sulphate of iron, &c. will be treated of in the next division.
The gas remaining instantly extinguished the taper, and was consequently nitrogene.
This experiment was repeated, with nearly the same results.
We may then conclude, that at high temperatures, nitrate of ammoniac is wholly resolved into water, nitrous acid, nitrous gas, and nitrogene; whilst a vivid luminous appearance is produced.
The transparency and orange color produced in the gas that had been clouded, by new portions of it, doubtless arose from the solution of the nitric acid and water forming the cloud, in the heated nitrous vapor produced, so as to constitute an aëriform triple compound; whilst the cloudiness and absorption subsequent were produced by the diminished temperature, which destroyed the ternary combination, and separated the nitrous acid and water from the nitrous gas.
From the rapidity with which the deflagration of nitrate of ammoniac proceeds, and from the immense quantity of light produced, it is reasonable to suppose that a very great increase of temperature takes place. The tube in which the decomposition has been effected, is always ignited after the process.
IX. _Speculations on the decompositions of Nitrate of Ammoniac._
All the phænomena of chemistry concur in proving, that the affinity of one body, A, for another, B, is not destroyed by its combination with a third, C, but only modified; either by condensation, or expansion, or by the attraction of C for B.
On this principle, the attraction of compound bodies for each other must be resolved into the reciprocal attractions of their constituents, and consequently the changes produced in them by variations of temperature explained, from the alterations produced in the attractions of those constituents.
Thus in nitrate of ammoniac, four affinities may be supposed to exist:
1. That of hydrogene for nitrogene, producing ammoniac.
2. That of oxygene for nitrous gas, producing nitric acid.
3. That of the hydrogene of ammoniac for the oxygene of nitric acid.
4. That of the nitrogene of ammoniac for the nitrous gas of nitric acid.
At temperatures below 300°, the salt, from the equilibrium between these affinities, preserves its existence.
Now when its temperature is raised to 400°, the attractions of hydrogene for nitrogene,[90] and of nitrous gas for oxygene,[91] are diminished; whilst the attraction of hydrogene for oxygene[92] is increased; and perhaps that of nitrogene for nitrous gas.
[90] As is evident from the decomposition of ammoniac by heat.
[91] Nitric acid is phlogisticated by heat, as appears from Dr. Priestley’s experiments. Vol. 3, p. 26.
[92] As is evident from the increase of temperature required for the formation of water.
Hence the former equilibrium of affinity is destroyed, and a new one produced.
The hydrogene of the ammoniac combines with the oxygene of the nitric acid to generate water; and the nitrogene of the ammoniac enters into combination with the nitrous gas to form nitrous oxide: and the water and nitrous oxide produced, most probably exist in binary combination in the aëriform state, at the temperature of the decomposition.
But when a heat above 800° is applied to nitrate of ammoniac, the attractions of nitrogene and hydrogene for each other, and of oxygene for nitrous gas,[93] are still more diminished; whilst that of nitrogene for nitrous gas is destroyed, and that of hydrogene for oxygene increased to a great extent: likewise a new attraction takes place; that of nitrous gas for nitric acid, to form nitrous vapor.[94] Hence a new arrangement of principles is rapidly produced; the nitrogene of ammoniac having no affinity for any of the single principles at this temperature, enters into no binary compound: the oxygene of the nitric acid forms water with the hydrogene, and the nitrous gas combines with the nitric acid to form nitrous vapor. All these substances most probably exist in combination at the temperature of their production; and at a lower temperature, assume the forms of nitrous acid, nitrous gas, nitrogene, and water.
[93] For ammoniac and nitrous oxide are both decomposed at the red heat, and oxygene given out from nitric acid when it is passed through a heated tube.
[94] Whenever nitrous acid is produced at high temperatures, it is always highly phlogisticated, provided it has not been long in contact with oxygene. When Dr. Priestley passed nitric acid through a tube heated red, he procured much oxygene, and phlogisticated acid; and the water in the apparatus employed was fully impregnated with nitrous air. Hence it would appear, that heat diminishes the attraction between oxygene and nitrous gas, and increases the affinity of nitrous gas for nitrous acid. Mr. JAMES THOMSON, whose theory of the Nitrous Acid I have already mentioned, from some experiments on the phlogistication of Nitric Acid by heat, which he has communicated to me, concludes with great justness, that a portion of the acid is always completely decomposed in this process: the oxygene liberated, and the nitrous gas combined with the remaining acid.
I have avoided entering into any discussions concerning the light and heat produced in this process; because these phænomena cannot be reasoned upon as isolated facts, and their relation to general theory will be treated of hereafter.
X. _On the preparation of Nitrous Oxide for experiments on Respiration._
When compact nitrate of ammoniac is slowly decomposed, the nitrous oxide produced is almost immediately fit for respiration; but as one part of the salt begins to decompose before the other is rendered fluid, a considerable loss is produced by sublimation.
For the production of large quantities of nitrous oxide, fibrous nitrate of ammoniac should be employed. This salt undergoes no decomposition till the greater part of its water is evaporated, and in consequence at the commencement of that process, is uniformly heated.
The gas produced from fibrous nitrate, must be suffered to rest at least for an hour after its generation. At the end of this time it is generally fit for respiration. If examined before, it will be found to contain more or less of a white vapor, which has a disagreeable acidulous taste, and strongly irritates the fauces and lungs. This vapor, most probably, consists of acid nitrate of ammoniac and water, which were dissolved by the gas at the temperature of its production, and afterwards slowly precipitated.
It is found in less quantity when compact nitrate is employed, because more salt is sublimed in this process, which being rapidly precipitated, carries with it the acid and water.
Whatever salt is employed, the last portions of gas produced, generally contain less vapor, and may in consequence be respired sooner than the first.
The nitrate of ammoniac should never be decomposed in a metallic vessel,[95] nor the gas produced suffered to come in contact with any metallic surface; for in this case the free nitric acid will be decomposed, and in consequence, a certain quantity of nitrous gas produced.
[95] Except it be gold or platina.
The apparatus that has been generally employed in the medical pneumatic institution, for the production of nitrous oxide, consists
1. Of a glass retort, of the capacity of two or three quarts, orificed at the top, and furnished with a ground stopper.
2. Of a glass tube, conical for the purpose of receiving the neck of the retort; about ,4 inches wide in the narrowest part, 4 feet long, curved at the extremity, so as to be capable of introduction into an airholder, and inclosed by tin plate to preserve it from injury.
3. Of airholders of Mr. Watt’s invention, filled with water saturated with nitrous oxide.
4. Of a common air-furnace, provided with dampers for the regulation of the heat.
The retort, after the insertion of the salt, is connected with the tube, carefully luted, and exposed to the heat of the furnace, on a convenient stand. The temperature is never suffered to be above 500°. After the decomposition has proceeded for about a minute, so that the gas evolved from the tube enlarges the flame of a taper, the curved end is inserted into the airholder, and the nitrous oxide preserved.
The water thrown out of the airholders in consequence of the introduction of the gas, is preserved in a vessel adapted for the purpose, and employed to fill them again; for if common water was to be employed in every experiment, a great loss of gas would be produced from absorption.
A pound of fibrous nitrate of ammoniac, decomposed at a heat not above 500°, produces nearly 5 cubic feet of gas; whilst from a pound of compact nitrate of ammoniac, rarely more than 4,25 cubic feet can be collected.
For the production of nitrous oxide in quantities not exceeding 20 quarts, a mode still more simple than that I have just described may be employed. The salt may be decomposed by the heat of an argands lamp, or a common fire, in a tubulated glass retort, of 20 or 30 cubic inches in capacity, furnished with a long neck, curved at the extremity; and the gas received in small airholders.
Thus, if the pleasurable effects, or medical properties of the nitrous oxide, should ever make it an article of general request, it may be procured with much less time, labor, and expence,[96] than most of the luxuries, or even necessaries, of life.
[96] A pound of nitrate of ammoniac costs about 5s. 10d. This pound, properly decomposed, produces rather more than 34 moderate doses of air; so that the expence of a dose is about 2d. What fluid stimulus can be procured at so cheap a rate?
DIVISION IV.
_EXPERIMENTS and OBSERVATIONS on the COMPOSITION of NITROUS GAS, and on its ABSORPTION by different bodies._
I. _Preliminaries._
In my account of the composition of nitric acid, in Division I. I gave an estimation of the quantities of oxygene and nitrogene combined in nitrous gas: I shall now detail the experiments on which that estimation is founded.
At an early period of my researches relating to nitrous oxide, from the observation of the phænomena taking place during the production of this substance, I had concluded, that the common opinion with regard to the composition of nitrous gas, was very distant from the truth. I had indeed analysed nitrous gas, by converting it into nitrous oxide, before I attempted to ascertain its composition by immediately separating the constituent principles from each other: and my first hopes of the possibility of effecting this, were derived from Dr. Priestley’s experiments on the combustion of pyrophorus in nitrous gas, and on the changes effected in it, by heated iron and charcoal.
This great philosopher found, that pyrophorus placed in contact with nitrous gas, burnt with great vividness, whilst the gas was diminished in volume to about one half, which generally consisted of nitrogene and nitrous oxide. He likewise found, iron heated by a lens in nitrous gas, increased in weight, whilst the gas was diminished about ½, and converted into nitrogene.[97]
He heated common charcoal, and charcoal of copper,[98] in nitrous gas by a lens. When common charcoal was employed, the gas was neither increased or diminished in bulk, but wholly converted into nitrogene; when charcoal of copper was used, the volume was a little increased, and the gas remaining consisted of ⁵/₇ nitrogene, and ²/₇ carbonic acid.
[97] Experiments and Observations, vol. II. pag. 50. Last Edition.
[98] That is, charcoal produced by the decomposition of spirits of wine. Vol. II. pag. 39.
In his experiments on the iron and pyrophyrus, the nitrous gas was evidently decomposed. From the great quantity of nitrogene produced in those on the charcoal, it seems likely that both the common charcoal,[99] and the charcoal of copper employed contained atmospherical air, which being dispelled by the heat of the lens, was decomposed by the nitrous gas: indeed, till I made the following experiment, I suspected that the carbonic acid produced, when the charcoal of copper was employed, arose from a decomposition of the nitrous acid, formed in this way.
[99] Dr. Priestley says, “having heated iron in nitrous air, I proceeded to heat in the same air, a piece of charcoal not long after it had been subjected to a strong heat covered with sand. The sun not shining immediately, after the charcoal was introduced into the vessel of air, through the mercury by which it was confined, part of the air was absorbed; but on heating the charcoal, the quantity was increased. Having continued the progress as long as I thought necessary, I examined the air and found it to be about as much as the original quantity of nitrous air; but it was all phlogisticated air extinguishing a candle and having no mixture of fixed air in it.”—Experiments and Observations, Vol. II, page 39.
I introduced a piece of well-burnt charcoal, which could hardly have weighed the eighth of a grain, whilst red hot, under a cylinder filled with mercury, and admitted to it half a cubic inch of nitrous gas. A slight absorption took place.
The sun being very bright, I kept the charcoal in the focus of a small lens for near a quarter of an hour. At the end of this time the gas occupied a space nearly as before the experiment, and a very minute portion of the charcoal had been consumed. On introducing into the cylinder a small quantity of solution of strontian, a white precipitation was perceived, and the gas slowly diminished to about three tenths of a cubic inch. To these three tenths a little common air was admitted, when very slight red fumes were perceived.
This experiment convinced me, that the attraction of charcoal for the oxygene of nitrous gas, at high temperatures, was sufficiently strong to effect a slow decomposition of it.
To be more accurately acquainted with this decomposition, and to learn the quantities of carbonic acid and nitrogene produced from a known quantity of nitrous gas, I proceeded in the following manner.
II. _Analysis of Nitrous Gas by Charcoal._