DIVISION III.
Decomposition of NITRATE of AMMONIAC: preparation of RESPIRABLE NITROUS OXIDE; its ANALYSIS.
I. Of the heat required for the decomposition of
NITRATE of AMMONIAC.
The decomposition of nitrate of ammoniac has been supposed by Cornette[78] to take place at temperatures below 212°, and its sublimation at 234°.
Kirwan, from the non-coincidence in the accounts of its composition, has imagined that it is partially decomposable, even by a heat of 80°.[79]
To ascertain the changes effected by increase of temperature in this salt, a glass retort was provided, tubulated for the purpose of introducing the bulb of a thermometer. After it had been made to communicate with the mercurial airholder, and placed in a furnace, the heat of which could be easily regulated, the thermometer was introduced, and the retort filled with the salt, and carefully luted; so that the appearances produced by different temperatures could be accurately observed, and the products evolved obtained.
From a number of experiments made in this manner on different salts, the following conclusions were drawn.
1st. Compact, or dry nitrate of ammoniac, undergoes little or no change at temperatures below 260°.
2dly. At temperatures between 275° and 300°, it slowly sublimes, without decomposition, or without becoming fluid.
3dly. At 320° it becomes fluid, decomposes, and still slowly sublimes; it neither assuming, or continuing in, the fluid state, without decomposition.
4thly. At temperatures between 340° and 480°, it decomposes rapidly.
5thly. The prismatic and fibrous nitrates of ammoniac become fluid at temperatures below 300°, and undergo ebullition at temperatures between 360° and 400°, without decomposition.
6thly. They are capable of being heated to 430° without decomposition, or sublimation, till a certain quantity of their water is evaporated.
7thly. At temperatures above 450° they undergo decomposition, without previously losing their water of crystalisation.
II. Decomposition of Nitrate of Ammoniac; production of
respirable Nitrous Oxide; its properties.
200 grains of compact nitrate of ammoniac were introduced into a glass retort, and decomposed slowly by the heat of a spirit lamp. The first portions of the gas that came over were rejected, and the last received in jars containing mercury. No luminous appearance was perceived in the retort during the process, and almost the whole of the salt was resolved into fluid and gas. The fluid had a faint acid taste, and contained some undecompounded nitrate. The gas collected exhibited the following properties.—
a. A candle burnt in it with a brilliant flame, and crackling noise. Before its extinction, the white inner flame became surrounded with an exterior blue one.
b. Phosphorus introduced into it in a state of inflammation, burnt with infinitely greater vividness than before.
c. Sulphur introduced into it when burning with a feeble blue flame, was instantly extinguished; but when in a state of active inflammation (that is, forming sulphuric acid) it burnt with a beautiful and vivid rose-colored flame.
d. Inflamed charcoal, deprived of hydrogene, introduced into it, burnt with much greater vividness than in the atmosphere.
e. To some fine twisted iron wire a small piece of cork was affixed: this was inflamed, and the whole introduced into a jar of the air. The iron burned with great vividness, and threw out bright sparks as in oxygene.
f. 30 measures of it exposed to water previously boiled, was rapidly absorbed; when the diminution was complete, rather more than a measure remained.
g. Pure water saturated with it, gave it out again on ebullition, and the gas thus produced retained all its former properties.
h. It was absorbed by red cabbage juice; but no alteration of color took place.
i. Its taste was distinctly sweet, and its odor slight, but agreeable.
j. It underwent no diminution when mingled with oxygene or nitrous gas.
Such were the obvious properties of the Nitrous Oxide, or the gas produced by the decomposition of nitrate of ammoniac in a temperature not exceeding 440°. Other properties of it will be hereafter demonstrated, and its affinities fully investigated.
III. Of the gas remaining after the absorption of
Nitrous Oxide by Water.
In exposing nitrous oxide at different times to rain or spring water, and water that had been lately boiled, I found that the gas remaining after the absorption was always least when boiled water was employed, though from the mode of production of the nitrous oxide, I had reason to believe that its composition was generally the same.
This circumstance induced me to suppose that some of the residuum might be gas previously contained in the water, and liberated from it in consequence of the stronger affinity of that fluid for nitrous oxide. But the greater part of it, I conjectured to consist of nitrogene produced in consequence of a complete decomposition of part of the acid, by the hydrogene. It was in endeavoring to ascertain the relative purity of nitrous oxide produced at different periods of the process of the decomposition of nitrate of ammoniac, that I discovered the true reason of the appearance of residual gas.
I decomposed some pure nitrate of ammoniac in a small glass retort; and after suffering the first portions to escape with the common air, I caught the remainder in three separate vessels standing in the same trough, filled with water that had been long boiled, and which at the time of the experiment was so warm that I could scarcely bear my hands in it. The different quantities collected gave the same intense brilliancy to the flame of a taper.
26 measures of each of them were separately inserted into 3 graduated cylinders, of nearly the same capacity, over the same boiled water. As the water cooled, the gas was absorbed by agitation. When the diminution was complete, the residuum in each cylinder filled, as nearly as possible, the same space; about two thirds of a measure.
To each of the residuums I added two measures of nitrous gas; they gave copious red vapor, and after the condensation filled a space rather less than two measures.
Hence the residual gas contained more oxygene than common air.
I now introduced 26 measures of gas from one of the vessels into a cylinder filled with unboiled spring water of the same kind.[80] After the absorption was complete, near two measures remained. These added to two measures of nitrous air, diminished to 2,5 nearly.
These experiments induced me to believe that the residual gas was not produced in the decomposition of nitrate of ammoniac, but that it was wholly liberated from the water.
To ascertain this point with precision, I distilled a small quantity of the same kind of water, which had been near an hour in ebullition, into a graduated cylinder containing mercury. To this I introduced about one third of its bulk, i. e. 12 measures of nitrous oxide, which had been carefully generated in the mercurial apparatus. After the absorption, a small globule of gas only remained, which could hardly have equalled one fourth of a measure. On admitting to this globule a minute quantity of nitrous gas, an evident diminution took place.
Though this experiment proved that in proportion as the water was free from air, the residuum was less, and though there was no reason to suppose that the ebullition and distillation had freed the water from the whole of the air it had held in solution, still I considered a decisive experiment wanting to determine whether nitrous oxide was the only gas produced in the slow decomposition of nitrate of ammoniac, or whether a minute quantity of oxygene was not likewise evolved.
I received the middle part of the product of a decomposition of nitrate of ammoniac, under a cylinder filled with dry mercury, and introduced to it some strong solution of ammoniac. After the white cloud produced by the combination of the ammoniacal vapor with the nitric acid suspended in the nitrous oxide, had been completely precipitated, I introduced a small quantity of nitrous gas. No white vapor was produced.
Now if any gas combinable with nitrous gas had existed in the cylinder, the quantity of nitrous acid produced, however small, would have been rendered perceptible by the ammoniacal fumes; for when a minute globule of common air was admitted into the cylinder, white clouds were instantly perceptible.
It seems therefore reasonable to conclude,
1. That the residual gas of nitrous oxide, is air previously contained in the water, (which in no case can be perfectly freed from it by ebullition), and liberated by the stronger attraction of that fluid for nitrous oxide.
2. That nitrate of ammoniac, at temperatures below 440°, is decompounded into pure nitrous oxide, and fluid.
3. That in ascertaining the purity of nitrous oxide from its absorption by water, corrections ought to be made for the quantity of gas dispelled from the water. This quantity in common water distilled under mercury being about ¹/₅₀; in water simply boiled, and used when hot, about ¹/₃₆; and in common spring water, ¹/₁₂.
IV. Specific gravity of Nitrous Oxide.
To understand accurately the changes taking place during the decomposition of nitrate of ammoniac, we must be acquainted with the specific gravity and composition of nitrous oxide.
90 cubic inches of it, containing about ¹/₃₅ common air, introduced from the mercurial airholder into an exhausted globe, increased it in weight 44,75 grains; thermometer being 51°, and atmospheric pressure 30,7.
106 cubic inches, of similar composition, weighed in like manner, gave at the same temperature and pressure nearly 52,25 grains; and in another experiment, when the thermometer was 41°, 53 grains.
So that accounting for the small quantity of common air contained in the gases weighed, we may conclude, that 100 cubic inches of pure nitrous oxide weigh 50,1 grains at temperature 50°, and atmospheric pressure 30,7.
I was a little surprised at this great specific gravity, particularly as I had expected, from Dr. Priestley’s observations, to find it less heavy than atmospherical air. This philosopher supposed, from some appearances produced by the mixture of it with aëriform ammoniac, that it was even of less specific gravity than that gas.[81]
V. Analysis of Nitrous Oxide.
The nitrous oxide may be analised, either by charcoal or hydrogene; during the combustion of other bodies in it, small portions of nitrous acid are generally formed, as will be fully explained hereafter.
The gas that I employed was generated from compact nitrate of ammoniac, and was in its highest state of purity, as it left a residuum of ¹/₃₈ only, when absorbed by boiled water.
10 cubic inches of it were inserted into a jar graduated to,1 cubic inches, containing dry mercury. Through this mercury a piece of charcoal which had been deprived of its hydrogene by long exposure to heat, weighing about a grain, was introduced, while yet warm. No perceptible absorption of the gas took place.[82]
Thermometer being 46°, the focus of a lens was thrown on the charcoal, which instantly took fire, and burnt vividly for about a minute, the gas being increased in volume. After the vivid combustion had ceased, the focus was again thrown on the charcoal; it continued to burn for near ten minutes, when the process stopped.
The gas, when the original pressure and temperature were restored, filled a space equal to 12,5 cubic inches.
On introducing to it a small quantity of strong solution of ammoniac[83], white vapor was instantly perceived, and after a short time the reduction was to about 10,1 cubic inches; so that apparently, 2,4 cubic inches of carbonic acid had been formed. The 10,1 cubic inches of gas remaining were exposed to water which had been long in ebullition, and which was introduced whilst boiling, under mercury. After the absorption of the nitrous oxide by the water, the gas remaining was equal to 5,3.
But on combining a cubic inch of pure nitrous oxide with some of the same water, which had been received under mercury in a separate vessel, nearly ¹/₂₂ remained. Consequently we may conclude, that 5,1 of a gas unabsorbable by water, was produced in the combustion.
This gas extinguished flame, gave no diminution with oxygene, and the slightest possible with nitrous gas. When an electric spark was passed through it, mingled with oxygene; no inflammation, or perceptible diminution took place.[84] We may consequently conclude that it was nitrogene, mingled with a minute portion of common air, expelled from the water.
The charcoal was diminished in bulk to one half nearly, but the loss of weight could not be ascertained, as its pores were filled with mercury.
Now 5 cubic inches of nitrous oxide were absorbed by the water, consequently 5 were decompounded by the charcoal; and these produced 5,1 cubic inches of nitrogene; and by giving their oxygene to the charcoal, apparently 2,4 of carbonic acid.
But 5 cubic inches of nitrous oxide weigh 2,5 grains, and 5,1 cubic inches of nitrogene 1,55; then 2,5-1,55 =,95.
So that reasoning from the relative specific gravities of nitrogene and nitrous oxide, 2,5 grains of the last are composed of 1,55 nitrogene, and,95 oxygene.
But from many experiments made on the specific gravity of carbonic acid, in August, 1799, I concluded that 100 cubic inches of it weighed 47,5 grains, thermometer being 60,1°, and barometer 29,5. Consequently, making the necessary corrections, 2,4 cubic inches of it weigh 1,14 grains; and on Lavoisier’s and Guyton’s[85] estimation of its composition, these 1,13 grains contain 8,2 of oxygene.
So that, drawing conclusions from the quantity of carbonic acid formed in this experiment, 2,5 grains of nitrous oxide will be composed of,82 oxygene, and 1,68 nitrogene.
The difference between these estimations is considerable, and yet not more than might have been expected, if we consider the probable sources of error in the experiment.
1. It is likely that variable minute quantities of hydrogene remain combined with charcoal, even after it has been long exposed to a red heat.
2. It is probable that the nitrogene and carbonic acid produced were capable of dissolving more water than that held in solution by the nitrous oxide; and if so, they were more condensed than if saturated with moisture, and hence the quantity of carbonic acid under-rated.
We may consequently suppose the estimation founded on the quantity of nitrogene evolved, most correct; and making a small allowance for the difference, conclude, that 100 grains of nitrous oxide are composed of about 37 oxygene, and 63 nitrogene; existing in a much more condensed state than when in their simple forms.
The tolerable accuracy of this statement will be hereafter demonstrated by a number of experiments on the combustion of different bodies in nitrous oxide, detailed in [Research II].
VI. Minute examination of the decomposition of Nitrate of Ammoniac.
Into a retort weighing 413,75 grains, and of the capacity of 7,5 cubic inches, 100 grains of pulverised compact nitrate of ammoniac were introduced. To the neck of this retort was adapted a recipient, weighing 711 grains, tubulated for the purpose of communicating with the mercurial airholder, and of the capacity of 8,3 cubic inches.
Temperature being 50° and atmospheric pressure 30,6, the recipient was inserted into a vessel of cold water, and made to communicate with the airholder. The heat of a spirit lamp was then slowly applied to the retort: the salt quickly began to decompose, and to liquify. The temperature was so regulated, as to keep up an equable and slow decomposition.
During this decomposition, no luminous appearance was perceived in the retort; the gas that came into the airholder was very little clouded, and much water condensed in the receiver.
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]
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.
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]
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]
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.
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.
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.
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.