Part 5

In my first experiments on the production of nitrate of ammoniac, I endeavoured to ascertain its composition by decompounding carbonate of ammoniac by nitric acid; and in making for this purpose, the analysis of carbonate of ammoniac, I discovered that there existed many varieties of this salt, containing very different proportions of carbonic acid, alkali, and water; the carbonic acid and water being superabundant in it, in proportion as the temperature of its formation was low, and the alkali in proportion as it was high: and not only that a different salt was formed at every different temperature, but likewise that the difference in them was so great, that the carbonate of ammoniac formed at 300° contained more than 50 per cent alkali, whilst that produced at 60° contained only 20.[73]

I found 210 grains of carbonate of ammoniac, which from comparison with other salts previously analised, I suspected to contain about 20 or 21 per cent alkali, saturated by 200 grains of nitric acid of 1,504. But though the carbonate was dissolved in much water, still, from the smell of the carbonic acid generated, I suspect that a small portion of the nitric acid was dissolved, and carried off by it. The solution, evaporated at about 200°, and afterwards exposed to a temperature below 300°, gave 232 grains of compact salt. But reasoning from the quantity of acid in 200 grains of nitric acid of 1,504, it ought to have given 245. Consequently 13 were lost by evaporation; and this loss agrees with that in the other experiments.

[73] A particular account of the experiments from which these facts were deduced, was printed in September, and will appear in the first volume of the _Researches_.

VI. _Decomposition of Sulphate of Ammoniac by Nitre._

As a cheap mode of obtaining nitrate of ammoniac, Dr. BEDDOES proposed to decompose nitre by sulphate of ammoniac, which is a well known article of commerce. From synthesis of sulphate of ammoniac, compared with analysis made in August 1799,[74] I concluded that 100 grains of prismatic salt were composed of about 18 grains ammoniac, 44 acid, and 38 water; and supposing 100 grains of nitre to contain 50 acid, 100 grains of sulphate of ammoniac will require for their decomposition 134 grains of nitre, and form 90,9 grains of compact nitrate of ammoniac.

[74] And which will be published, with an account of its perfect decomposition at a high temperature, in the _Researches_.

To ascertain if the sulphate of potash and nitrate of ammoniac could be easily separated, I added to a heated saturated solution of sulphate of ammoniac, pulverised nitre, till the decomposition was complete. After this decomposition, the solution contained a slight excess of sulphuric acid, which was combined with lime, and the whole set to evaporate at a temperature below 250°. As soon as the sulphate of potash began to crystalise, the solution was suffered to cool, and then poured off from the crystalised salt, which appeared to contain no nitrate of ammoniac. After a second evaporation and crystalisation, almost the whole of the sulphate appeared to be deposited, and the solution of nitrate of ammoniac was obtained nearly pure: it was evaporated at 212°, and gave fibrous crystals.

VII. _Non-existence of Ammoniacal Nitrites._

I attempted in different modes to combine _nitrous_ acids with ammoniac, so as to form the salts which have been supposed to exist, and called _nitrites_ of ammoniac; but without success.

I first decomposed a solution of carbonate of ammoniac by dilute olive colored acid; but in this process, though no heat was generated, yet all the nitrous gas appeared to be liberated with the carbonic acid.[75] I then combined a small quantity of nitrous gas, with a solution of nitrate of ammoniac. But after evaporating this solution at 70°-80°, I could not detect the existence of nitrous gas in the solid salt; it was given out during the evaporation and crystalisation, and formed into nitrous acid by the oxygene of the atmosphere. I likewise heated nitrate of ammoniac to different degrees, and partially decomposed it, to ascertain if in any case the acid was phlogisticated by heat: but in no experiment could I detect the existence of _nitrous_ acid in the heated salt, when it had been previously perfectly neutralised.

[75] When nitrous gas exists in neutro-saline solutions, they are always colored more or less intensely, from yellow to olive, in proportion to the quantity combined with them.

When nitrate of ammoniac, indeed, with excess of nitric acid, is exposed to heat, the superabundant nitric acid becomes phlogisticated, and is then liberated from the salt, which remains neutral.[76]

[76] Hence a nitrate of ammoniac with excess of acid, when exposed to heat, first becomes yellow, and then white.

We may therefore conclude that nitrous gas has little or no affinity for solid nitrate of ammoniac, and that no substance exists to which the name _nitrite_ of ammoniac can with propriety be applied.

VIII. _Of the sources of error in Analysis._

To compare my synthesis of nitrate of ammoniac with analysis, I endeavoured to separate the ammoniac and nitric acid from each other, without decomposition. But in going through the analytical process, I soon discovered that it was impossible to make it accurate, without many collateral laborious experiments on the quantities of ammoniac soluble in water at different temperatures.

At a temperature above 212°, I decomposed, by caustic slacked lime, 50 grains of compact nitrate of ammoniac in a retort communicating with the mercurial airholder, the moisture in which had been previously saturated with ammoniac. 22 cubic inches of gas were collected at 38°, and from the loss of weight of the retort, it appeared that 13 grains of solution of ammoniac in water, had been deposited by the gas.

Now evidently, this solution must have contained much more alkali in proportion to its water than that of 55°, otherwise the quantity of ammoniac in 50 grains of salt would hardly equal 8 grains.[77]

[77] The accounts given by different chemists of the composition of nitrate of ammoniac, are extremely discordant; they have been chiefly deduced from decompositions of carbonate of ammoniac (the varieties of which have been heretofore unknown) by nitrous acids of unknown degrees of nitration. Hence they are particularly erroneous with regard to the alkaline part. Wenzel supposes it to be 32 per cent, and Kirwan 24. _Addit. Observ._ pag. 120.

IX. _Of the loss of Solutions of Nitrate of Ammoniac during evaporation._

The most concentrated solution of nitrate of ammoniac capable of existing at 60°, is of specific gravity 1,304, and contains 33 water, and 67 fibrous salt, per cent. When this solution is evaporated at temperatures between 60° and 100, the salt is increased in weight by the addition of water of crystalisation, and no portion of it is lost.

During the evaporation of solutions of specific gravity 1,146 and 1,15, at temperatures below 120°, I have never detected any loss of salt. When the temperature of evaporation is 212°, the loss is generally from 3 to 4 grains per cent; and when from 230° to the standard of their ebullition, from 4 to 6 grains.

In proportion as solutions are more diluted, their loss in evaporation at equal temperatures is greater.

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]

[78] Mem. Par. 1783. See Irish Trans. vol. 4.

[79] Addit. Obs. pag. 120.

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.

[80] Two measures of air dispelled from this water by boiling, mingled with 2 of nitrous gas, diminished to 2,4 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]

[81] Experiments and Observations, vol. 2, pag. 89. Last Edition.

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]

[82] A minute quantity, however, must have been absorbed, and given out again when the charcoal was heated.

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.

[83] Strong solution of ammoniac has no attraction for nitrous oxide.

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.

[84] The gas was examined by those tests in order to prove that no water had been decomposed.

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.

[85] See the curious paper of this excellent philosopher, on the combustion of the diamond, in which he proves that charcoal is, in fact, oxide of diamond. Annales de Chimie, xxxi.

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.