Chapter II: Part 2

From the diminution of specific gravity of nitric acid by combination with nitrous gas, and from the smaller attraction of nitric acid for nitrous gas, in proportion as it is diluted, it is probable that the nitrated acids, in their combinations with water, do not contract so much as[42] nitric acids of the same specific gravities. The affinities resulting from the small attraction of nitrous gas for water, and its greater attraction for nitric acid, must be such as to lessen the affinity of nitric acid and water for each other.

[41] A great portion of it, of course, dissolved in the water with the nitrous acid carried over.

[42] Their changes of volume, corresponding to changes of temperature, most probably, are likewise different.

Hence it would require an infinite number of experiments to ascertain the real quantities of acid, nitrous gas, and water, contained in the different diluted nitrous acids; and after these quantities were determined, they would probably have no important connection with the chemical arrangement. As yet, our instruments of experiment are not sufficiently exact to afford us the means of ascertaining the ratio in which the attraction of nitric acid[43] for water diminishes in its progress towards saturation.

[43] Probably in the ratio of the square of the quantity of water united to it.

The estimations in the following table, of the real quantities of nitric acid in solutions of different specific gravities, were deduced from experiments made in the manner described in section VI, except that the phial employed was longer, narrower, and graduated to half grains. The temperature, at the time of combination, was from 40° to 46°.

TABLE III.

_Of the Quantities of True NITRIC ACID in solutions
of different SPECIFIC GRAVITIES._

+----------------+-----+-------------+-------+
|100 Parts Nitric| |True Acid[44]| Water |
|Acid of specific| | | |
| gravity | | | |
+----------------+ +-------------+-------+
| 1,5040 | c | 91,55 | 8,45 |
| 1,4475 | o | 80,39 | 19,61 |
| 1,4285 | n | 71,65 | 28,35 |
| 1,3906 | t | 62,96 | 37,04 |
| 1,3551 | a | 56,88 | 43,12 |
| 1,3186 | i | 52,03 | 47,97 |
| 1,3042 | n | 49,04 | 50,96 |
| 1,2831 | | 46,03 | 53,97 |
| 1,2090 | | 45,27 | 54,73 |
+----------------+-----+-------------+-------+

[44] The quantities of Oxygene and Nitrogene in any solution, may be thus found—— Let A = the true acid, X the oxygene, and Y the nitrogene.

Then

238 A A
X = —————— and Y = ————
239 239

XII. The blue green spherules mentioned in section V. produced by the condensation of nitrous vapor, and by the combination of nitric acid with nitrous gas, may be considered as saturated solutions of nitrous gas in nitric acid. The combinations of nitric acid and nitrous gas containing a larger proportion of nitrous gas, are incapable of existing in the fluid state at common temperatures; and, as appears from the first experiment, an increase of volume takes place during their formation. They consequently ought to be looked upon as solutions of nitric acid in nitrous gas, identical with the nitrous vapor of Priestley.

From the researches of this great discoverer, we learn that nitrous vapor is decomposable, both by water and mercury. Hence it is almost impossible accurately to ascertain its composition. In one of his experiments,[45] when more than 130 grains of strong nitrous acid were exposed for two days to nearly 247 cubic inches of nitrous gas, over water: about half of the acid was dissolved, and deposited with the gas in the water.[46]

[45] Experiments and Observations; last edition, vol. 1, page 384.

[46] Nitrous gas, holding in solution nitrous acid, is more readily absorbed by water than when in its pure form, from being presented to it in a more condensed state in the green acid, formed by the contact of water and nitrous vapor.

XIII. In comparing the results of my fundamental experiment on the composition of nitrous acid, with those of Cavendish, the great coincidence between them gave me very high satisfaction, as affording additional proofs of accuracy. If the acid formed in the last experiment of this illustrious philosopher be supposed analogous to the light green acid formed in my first experiment, our estimations will be almost identical.

Lavoisier’s account of the composition of the nitric and nitrous acids, has been generally adopted. According to his estimation, these substances contain a much larger quantity of oxygene than I have assigned to them.

The fundamental experiments of this great philosopher were made at an early period of pneumatic chemistry,[47] on the decomposition of nitre by charcoal; and he considered the nitrogene evolved, and the oxygene of the carbonic acid produced in this process, as the component parts of the nitric acid contained in the nitre.

[47] Mem. des Savans Etrangers, v. xi. 226. Vide Kirwan sur le phlogistique pag. 110.

I have before mentioned the liberation of nitrous acid, in the decomposition of nitre by combustible bodies; and I had reasons for suspecting that this circumstance was not the only source of inaccuracy.

That my suspicions were well founded, will appear from the following experiments:

EXPERIMENT _a_. I introduced into a strong glass tube, 3 inches long, and nearly,3 wide, a mixture of 10 grains of pulverised, well burnt charcoal, and 60 grains of nitre. It was fired by means of touch-paper, and the tube instantly plunged under a jar filled with dry mercury. A quantity of gas, clouded with dense white vapor was collected. When this vapor was precipitated, so that the surface of the mercury could be seen, it appeared white, as if acted on by nitrous acid. On introducing a little oxygene into the jar, copious red fumes appeared.

EXP. _b_. A similar mixture was fired[48] under the jar, the top of the mercury being covered with a small quantity of red cabbage juice, rendered green by an alkali. This juice, examined when the vapor was precipitated, was become red, and on introducing to it a little carbonate of potash, a slight effervescence took place.

[48] In this experiment, as well as in the last, some of the mixture was thrown into the jar undecompounded.

EXP. _c_. Five grains of charcoal, and 20 of nitre, were now fired in the same manner as before, the mercury being covered with a stratum of water. After the precipitation of the vapor on the introduction of oxygene, no red fumes were perceived.

EXP. _d_. 30 grains of nitre, 5 of charcoal, and five of silicious earth,[49] were now mingled and fired. The gas received under mercury was composed of 18 carbonic acid, and nearly 12 nitrogene.[50] A little muriatic acid was poured on the residuum in the tube; a slight effervescence took place.

[49] To detach the potash from the carbonic acid.

[50] This nitrogene contained a little nitrous gas, as it gave red fumes when exposed to the air. The free nitrous acid was decomposed by the mercury, as it was not covered with water.

EXP. _e_. The top of the mercury in the jar was now covered with a little diluted muriatic acid, and a small glass tube filled with a mixture of 3 grains of charcoal, and 20 nitre. After the deflagration, the tube itself with the residuum it contained, were thrown into the jar. The carbonic acid was quickly detached from them by the muriatic acid, and the whole quantity of gas generated in the process, obtained; it measured 15 cubic inches.

4 cubic inches of it exposed to solution of potash, diminished to 1⁴/₁₀; 7 of the remainder, with 8 of oxygene, gave only 12.

EXP. _f_. 60 grains of nitre, and 9 of charcoal were fired, the top of the mercury in the jar being covered with water. After the deflagration, the tube that had contained them was introduced, and the carbonic acid contained by the carbonate of potash, disengaged by muriatic acid. 30 measures of the gases evolved were exposed to caustic potash; 20 exactly were absorbed, the 10 remaining, with 10 of oxygene, diminished to 17.

EXP. _g_. A mixture of nitre and charcoal were deflagrated over a little water in the mercurial jar: after the precipitation of the vapor, the water was absorbed by filtrating paper. This filtrating paper, heated in a solution of potash, gave a faint smell of ammoniac.

EXP. _h_. Water impregnated with the vapor produced in the deflagration, was heated with quicklime, and presented separately to three persons accustomed to chemical odors. Two of them instantly recognised the ammoniacal smell, the other could not ascertain it. Paper reddened with cabbage juice was quickly turned green by the vapor.

These experiments are sufficient to shew that the decomposition of nitre by charcoal is a very complex process, and that the intense degree of heat produced may effect changes in the substances employed, which we are unable to estimate.

The products, instead of being simply carbonic acid, and nitrogene, are carbonic acid, nitrogene, nitrous acid, probably ammonia, and sometimes nitrous gas. The nitrous acid is disengaged from the base by the intense heat. Concerning the formation of the ammonia, it is useless to reason till we have obtained unequivocal testimonies of its existence; it may be produced either by the decomposition of the water contained in the nitre, by the combination of its oxygene with the charcoal, and of its nascent hydrogene with the nitrogene of the nitric acid; or from some unknown decomposition of the potash.

As neither Lavoisier nor Berthollet found nitrous gas produced in the decomposition of nitre by charcoal, when a water apparatus was employed; and as it was not uniformly evolved in my experiments, the most probable supposition is, that it arises from the decomposition of a portion of the free nitrous acid intensely heated, by the mercury.

In none of my experiments was the whole of the nitre and charcoal decomposed, some of it was uniformly thrown with the gases into the mercurial apparatus. The nitrogene evolved, as far as I could ascertain by the common tests, was mingled with no inflammable gas.

If we consider experiment _f_ as accurate, with regard to the relative quantities of carbonic acid and nitrogene produced, they are to each other nearly as 20 to 8; that is, allowing 2 for the nitrous gas, and consequently, reasoning in the same manner as Lavoisier, concerning the composition of nitric acid, it should be composed of 1 nitrogene to 3,38 oxygene. But though the quantity of oxygene in this estimation is far short of that given in his, yet still it is too much. From whatever source the errors arise, whether from the evolution of phlogisticated nitrous acid, or the decomposition of water, or the production of nitrous gas, they all tend to increase the proportion of the carbonic acid to the nitrogene.

I am unacquainted with any experiment from which accurate opinions concerning the different relative proportions of oxygene and nitrogene in the nitric and nitrous acids could be deduced. Lavoisier’s calculation is founded on his fundamental experiment, and on the combination of nitrous gas and oxygene.

Dr. Priestley’s experiment mentioned in section 12, on the absorption of nitrous gas by nitrous acid, from which Kirwan[51] deduces the composition of the differently colored nitrous acids, was made over water, by which, as is evident from a minute examination of the facts[52], the greater portion of the nitrous gas employed was absorbed.

[51] Essay on phlogiston.

[52] Dr. Priestley says, “Having filled a phial containing exactly the quantity of four pennyweights of water, with strong, pale, yellow spirit of nitre, with its mouth quite close to the top of a large receiver standing in water, I carefully drew out almost all the common air, and then filled it with nitrous air; and as this was absorbed, I kept putting in more and more, till in less than two days it had completely absorbed 130 ounce measures. Presently after this process began, the surface of the acid assumed a deep orange color, and when 20 or 30 ounce measures of air were absorbed, it became green at the top: this green descended lower and lower, till it reached the bottom of the phial. Towards the end of the process, the evaporation was perceived to be very great, and when I took it out, the quantity was found to have diminished to one half. Also it had become, by means of this process, and the evaporation together, exceeding weak, and was rather blue than green.”

_Experiments and Observations_, vol. 1, p. 384. Last edition. XIV. The opinions heretofore adopted respecting the quantities of real or true acid in solutions of nitrous acid of different specific gravities, have been founded on experiments made on the nitro-neutral salts, the most accurate of which are those of Kirwan, Bergman, and Wenzel. The great difference in the results of these celebrated men, proves the difficulty of the investigation, and the existence of sources of error.[53] Kirwan deduces the composition of the solutions of nitrous acid in water, from an experiment on the formation of nitrated soda. In this experiment, 36,05 grains of soda were saturated by 145 grains of nitrous acid, of specific gravity 1,2754. By a test experiment, he found the quantity of salt formed to be 85,142 grains.[54] Hence he concludes that 100 parts of nitrous acid, of specific gravity 1,5543, contain 73,54 of the strongest, or most concentrated acid.

[53] See Mr. Keir’s excellent observations on this subject. Chem. Dict. Art. Acid.

[54] Irish Transactions, vol. 4, p. 34.

Supposing his estimation perfectly true, 100 parts of the aëriform acid of 55° would be composed of 74,54 of his real acid, and 25,46 water. In examining, however, one of his later experiments,[55] we shall find reasons for concluding, that the acid in nitrated soda cannot contain much less water than the aëriform acid. A solution of carbonated soda, containing 125 grains of real alkali, was saturated by 306,2 grains of nitrous acid, of specific gravity 1,416. The evaporation was carried on in a temperature not exceeding 120°, and the residuum exposed to a heat of 400° for six hours, at the end of which time it weighed 308 grains. Now according to my estimation, 306 grains of nitric acid, of 1,416, should contain 215 true acid; and we can hardly suppose, but that during the evaporation and consequent long exposure to heat, some of the nitrated soda was lost with the water.

[55] Addit. Obs. pag. 74.

Bergman estimates the quantity of water in this salt at 25, and the acid at 43 per cent; but his real acid was not so concentrated as Kirwan’s, consequently the nitric acid in nitrated soda should contain more water than my true acid.

Wenzel, from an experiment on the composition of nitrated soda, concludes that it contains 37,48 of alkali, and 62,52 of nitrous acid; and 1000 of this acid, from Kirwan’s calculation, contain 812,6 of his real acid; consequently, 100 parts of my aëriform acid should contain 93,28 of Wenzel’s acid, and 6,72 of water.

I saturated with potash 54 grains of solution of nitric acid, of specific gravity 1,301. Evaporated at about 212°, it produced 66 grains of nitre. This nitre exposed to a higher temperature, and kept in fusion for some time, was reduced to 60 grains.

Now from the table, 54 of 1,301, should contain 26,5 of true acid. But according to Kirwan’s estimation, 100 parts of dry nitre contain 44[56] of his real acid, with 4 water; consequently 60 should contain 26,4.

[56] Additional Observations, page 70.

Again, 90 grains of acid, of specific gravity 1,504, saturated with potash, and treated in the same manner, gave 173 grains of dry nitre. Consequently, 100 parts of it should contain 47,3 grains of true acid.

Now Lavoisier[57] allows about 51 of dry acid to 100 grains of nitre, and Wenzel 52.

From Berthollet’s[58] experiments, 100 grains of nitre, in their decomposition by heat, give out nearly 49 grains of gas.[59]

Hence it appears that the aëriform acid, that is, the true acid of my table, contains rather less water than the acid supposed to exist in nitre.

[57] Elements, pag. 103, Kerr’s Translation.

[58] Mem. Acad. 1787.

[59] As well as oxygene and nitrogene, Mr. Watt’s experiments prove that much phlogisticated nitrous acid is produced.

DIVISION II.

_EXPERIMENTS and OBSERVATIONS on the composition of
AMMONIAC and on its combinations with WATER and
NITRIC ACID._

I. _Analysis of AMMONIAC or VOLATILE ALKALI._

The formation and decomposition of volatile alkali in many processes, was observed by Priestley, Scheele, Bergman, Kirwan, and Higgins; but to Berthollet we owe the discovery of its constituent parts, and their proportions to each other. These proportions this excellent philosopher deduced from an experiment on the decomposition of aëriform ammoniac by the electric spark:[60] a process in which no apparent source of error exists.

[60] Journal de Physique, 1786. Tom. 2, pag. 176.

Since, however, his estimations have been made, the proportions of oxygene and hydrogene in water have been more accurately determined. This circumstance, as well as the conviction of the impossibility of too minutely scrutinizing facts, fundamental to a great mass of reasoning, induced me to make the following experiments.

A porcelain tube was provided, open at both ends, and well glazed inside and outside, its diameter being about,5 inches. To one end of this, a glass tube was affixed, curved for the purpose of communicating with the water apparatus. With the other end a glass retort was accurately connected, containing a mixture of perfectly caustic slacked lime, and muriate of ammoniac.

The water in the apparatus for receiving the gases had been previously boiled, to expel the air it might contain, and during the experiment was yet warm.

When the tube had been reddened in a furnace adapted to the purpose, the flame of a spirit lamp was applied to the bottom of the retort. A great quantity of gas was collected in the water apparatus; of this the first portions were rejected, and the last transferred to the mercurial trough.

A small quantity examined, did not at all diminish with nitrous gas, and burnt with a lambent white flame, in contact with common air.

2¾ of this gas, equal to 110 grain measures, were fired with 2, equal to 80, of oxygene, in a detonating tube, by the electric spark. They were reduced to 2¼, or 90. On introducing to the remainder a solution of strontian, it became slightly clouded on the top, and an absorption of some grain measures took place.

It was evident, then, that in this experiment, charcoal[61] had been somehow present in the tube; which being dissolved by the nascent hydrogene, had rendered it slightly carbonated, and in consequence made the results inconclusive.

[61] Though the tube had never been used, and was apparently clean and dry on the inside, it must have contained something in the form of dust, capable of furnishing either hydrocarbonate, or charcoal.

A tube of thick green glass carefully made clean, was now employed, inclosed in the porcelain tube. Every other precaution was taken to prevent the existence of sources of error, and the experiment conducted as before.

140 grain measures of the gas produced, fired with 120 of oxygene, left, in two experiments, nearly 110. Solution of strontian placed in contact with the residuum, did not become clouded, and no absorption was perceived.

Now 150 measures of gas were destroyed, and if we take Lavoisier’s and Meusnier’s estimation of the composition of water, and suppose the weight of oxygene to be 35 grains, and that of hydrogene 2,6 the hundred cubic inches; the oxygene employed will be to the hydrogene as 243 to 576. Put _x_ for the oxygene, and _y_ for the hydrogene.

Then _x_ + _y_ = 150

_x_ : _y_ :: 243 : 576

243_y_
_x_ = ——————
576

819_y_ = 86400

_y_ = 105 _x_ = 45

And 140 - 105 = 35

Consequently, the nitrogene in ammoniac is to the hydrogene as 35: 105 in volume: and 13,3 grains of ammoniac are composed of 10,6 nitrogene, (supposing that 100 cubic inches weigh 30,45 grains) and 2,7 hydrogene.

According to Berthollet, the weight of the nitrogene in ammoniac is to that of the hydrogene as 121 to 29.[62] The difference between this estimation and mine is so small as to be almost unworthy of notice, and arises most probably from the slight difference between the accounts of Lavoisier and Monge, of the composition of water, and the different weights assigned to the gases employed.

[62] Journal de Physique, 1786, t. 2, 177.

We may then conclude, that 100 grains of ammoniac are composed of about 80 nitrogene, and 20 hydrogene.

The decomposition of ammoniac by heat, as well as by the electric spark, was first discovered by Priestley. In an experiment[63] when aëriform ammoniac was sent through a heated tube from a caustic solution of ammoniac in water, this great discoverer observed that an inflammable gas was produced, though in no great quantity, and that a fluid blackened by matter, probably carbonaceous, likewise came over.

[63] Phil. Trans. vol. 79, page 294.

In my experiments the whole of the ammoniac appeared to be decomposed; the quantity of gas generated was immense, and not clouded, as is usually the case with gases generated at high temperatures. It is possible, that the larger quantity of water carried over in his experiment, by its strong attraction for ammoniac in the aëriform state, might have, in some measure, retarded the decomposition. It is however, more probable to suppose, that a fissure existed in the earthen tube he employed, through which a certain quantity of gas escaped, and coaly matter entered.

Priestley found that the metallic oxides when strongly heated, decomposed ammoniac, the metal being revivified and water and nitrogene produced.[64] The estimations of the composition of ammoniac that may be deduced from his experiments on the oxide of lead, differ very little from those already detailed.

[64] Vol. 2, page 398.

II. _Specific gravity of Ammoniac._

From the great solubility of ammoniac in water, it is difficult to ascertain its specific gravity in the same manner as that of a gas combinable to no great extent with that fluid. It is impossible to prevent the existence of a small quantity of solution of ammoniac in the mercurial airholder,[65] or apparatus containing the gas; and during the diminution of the pressure of the atmosphere on this solution,[66] a certain quantity of gas is liberated from it, and hence a source of error.

[65] Ammoniac generated at a temperature above that of the atmosphere, always deposits ammoniacal solution during its reduction to the common temperature.

[66] By the introduction of aëriform ammoniac into the exhausted globe.

To ascertain, then, the weight of ammoniac, I employed an apparatus similar to that used for the absorption of nitrous gas by nitric acid.

50 cubic inches of gas were collected in the mercurial airholder, from the decomposition of muriate of ammoniac by lime; thermometer being 58°, and barometer 29,6.

100 grains of diluted sulphuric acid were introduced into the small graduated cylinder, which after being carefully weighed, was made to communicate with the airholder, the curved tube containing a small quantity of water. The gas was slowly passed into the fluid, and the globules wholly absorbed before they reached the top; much increase of temperature being consequent. When the absorption was compleat, the phial was increased in weight exactly 9 grains.

This experiment was repeated three times. The difference of weight, which was probably connected with alterations of temperature and pressure, never amounted to more than one sixth of a grain.

We may then conclude, that at temperature 58°, and atmospheric pressure 29,6, 100 cubic inches of ammoniac weigh 18 grains.

According to Kirwan, 100 cubic inches of alkaline air[67] weigh 18,16 grains; barometer 30°, thermometer 61. The difference between these estimations, the corrections for temperature and pressure being made, is trifling.

[67] Additional Observations, page 107.

III. _Of the quantities of true Ammoniac in Aqueous Ammoniacal Solutions, of different specific gravities._

To ascertain the quantities of ammoniac, such as exists in the aëriform state, saturated with moisture, in solutions of different specific gravities, I employed the apparatus for absorption so often mentioned. Thermometer being 52°, the mercurial airholder was filled with ammoniacal gas, and the graduated phial, containing 50 grains of pure water, connected with it. During the absorption of the gas, the phial became warm. When about 30 cubic inches had been passed through, it was suffered to cool, and weighed: it had gained 5,25 grains, and the fluid filled a space equal to that occupied by 57[68] grains of water.

[68] It is necessary in these experiments, that the greatest care be observed in the introduction and extraction of the capillary tube. If it is introduced dry, there will be a source of error from the moisture adhering to it when taken out. I therefore always wetted it before its introduction, and took care that no more fluid adhered to it after the experiment, than before.

Consequently, 100 grains of solution of ammoniac in water of specific gravity,9684 contain 9,502 grains of ammoniac.

The apparatus being adjusted as before, 50 grains of pure water were now perfectly saturated with ammoniac. They gained in weight 17 grains, and when perfectly cool, filled a space equal to 74 of water. Consequently 100 grains of aqueous ammonial solution of specific gravity,9054 contain 25,37 grams of ammoniac.

The two solutions were mingled together; but no alteration of temperature took place. Consequently the resulting specific gravity might have been found by calculation.

On mingling a large quantity of caustic solution of ammoniac with ¼ of its weight of water, of exactly the same temperature, no alteration of it was perceptible by a sensible thermometer.—Hence the two experiments[69] being assumed as data, the intermediate estimations in the following table, were found by calculation.

[69] Previous to those experiments, I had made a number of others on the combination of ammoniac with water.—My design was, to ascertain the diminution of specific gravity for every three grains of ammoniac absorbed; but this I found impossible. The capillary tube, when taken out of the phial, always carried with it a minute portion of the solution, which partially evaporated before it could be again introduced; and thus the sources of error increased in proportion to the number of examinations.

TABLE IV.

_Of approximations to the quantities of AMMONIAC,
such as exists in the aëriform state, saturated with
water at 52°, in AQUEOUS AMMONIACAL SOLUTIONS of
different specific gravities._

+----------+-----+----------+--------+
| 100 | | Ammoniac.| Water. |
| Specific | | | |
| Gravity. | | | |
+----------+ +----------+--------+
| 9054 | | 25,37 | 74,63 |
| 9166 | | 22,07 | 77,93 |
| 9255 | | 19,54 | 80,46 |
| 9326 | c | 17,52 | 82,48 |
| 9385 | o | 15,88 | 84,12 |
| 9435 | n | 14,53 | 85,47 |
| 9476 | t | 13,46 | 86,54 |
| 9513 | a | 12,40 | 87,60 |
| 9545 | i | 11,56 | 88,44 |
| 9573 | n | 10,82 | 89,18 |
| 9597 | | 10,17 | 89,83 |
| 9619 | | 9,60 | 90,40 |
| 9684 | | 9,50 | 90,50 |
| 9639 | | 9,09 | 90,91 |
| 9713 | | 7,17 | 92,83 |
+----------+-----+----------+--------+
As yet no mode has been discovered for obtaining
gases in a state of absolute dryness; consequently
we are ignorant of the different quantities
of water they hold in solution at different
temperatures. As far as we are acquainted with
the combinations of ammoniac, there is no state
in which it exists so free from moisture, as when
aëriform, at low temperatures.

That no considerable source of error existed in the two experiments, is evident from the trifling difference between the estimations of the quantities of real ammoniac, in the solution of,9684, as found in the first experiment, and as given by calculation from the last.

The quantity of ammoniac in a solution of specific gravity not in the table, may be thus determined—find the difference between the two specific gravities nearest to it in the table; _d_, and the difference between their quantities of alkali, _b_; likewise the difference between the given specific gravity and that nearest to it, _c_.

then _d_ : _b_ :: _c_ : _x_

_bc_
and _x_ = —————
_d_

Which, added to the quantity of the lower specific gravity, is the alkali sought.

The differences in specific gravity of the solutions of ammoniac at temperatures between 4O° and 65°[70] are so trifling as to be hardly ascertainable, by our imperfect instruments, and consequently are unworthy of notice.

[70] The expansion from increase of temperature is probably great in proportion to the quantity of ammoniac in the solution.

It is possible at very low temperatures to obtain ammoniacal solutions of less specific gravity than,9, but they are incapable of being kept for any length of time under the common pressure of the atmosphere.

IV. _Combinations of Ammoniac with Nitric Acid, Composition of Nitrate of Ammoniac, &c._

200 grains of ammoniacal solution, of specific gravity,9056, were saturated by 385,5 grains of nitric acid, of specific gravity 1,306. The combination was effected in a long phial, the nitrous acid added very slowly, and the phial closed after every addition, to prevent any evaporation in consequence of the great increase of temperature.[71] The specific gravity of the solution, when reduced to the common temperature, was 1,15. Evaporated at a heat of 212°,[72] it gave 254 grains of salt of fibrous crystalization. This salt was dissolved in 331 grains of water; the specific gravity of the solution was 1,148 nearly.

[71] From the combination.

[72] I had before proved that at this temperature the salt neither decomposed nor sublimed.

Hence it was evident that some of the salt had been lost during the evaporation.

To find the quantity lost, fibrous nitrate of ammoniac was dissolved in small quantities in the solution, the specific gravity of which was examined after every addition of 3 grains. When 16 grains had been added to it, it became of 1,15.

Consequently, the solution composed of 200 grains of ammoniacal, and of 385,5 of nitric acid solution, contained 262 grains of salt of fibrous crystalization, and of this salt 8 grains were lost during the evaporation.

But the alkali in 200 grains of ammoniacal solution of,9056 = 50,5 grains. And the true nitric acid in 385,5 grains of solution of 1,306 = 190 grains.

Then 262-240,5 = 21,5, the quantity of water.

And 262 grains of fibrous crystalized nitrate of ammoniac, contain 190 grains true acid, 50,5 ammoniac, and 21,5 water. And 100 parts contain 72,5 acid. 19,3 ammoniac, and 8,2 water.

In proportion as the temperature employed for the evaporation of nitro-ammoniacal solutions, is above or below 212°, so in proportion does the salt produced contain more or less water than the fibrous nitrate. But whatever may have been the temperature of evaporation, the acid and alkali appear always to be in the same proportions to each other.

Of the salts containing different quantities of water, two varieties must be particularly noticed. The prismatic nitrate of ammoniac, produced at the common temperatures of the atmosphere, and containing its full quantity of water of crystalisation; and the compact nitrate of ammoniac, either amorphous, or composed of delicately needled crystals, formed at 300°, and containing but little more water than exists in nitric acid and ammoniac.

To discover the composition of the prismatic nitrate of ammoniac, 200 grains of fibrous salt were dissolved in the smallest possible quantity of water, and evaporated in a temperature not exceeding 70°. The greater part of the salt was composed of perfectly formed tetrahædral prisms, terminated by tetrahædral pyramids. It had gained in weight about 8,5 grains.

Consequently 100 grains of prismatic nitrate of ammoniac may be supposed to contain 69,5 acid, 18,4 ammoniac, and 12,1 water.

To ascertain the composition of the compact nitrate of ammoniac, I exposed in a deep porcelain cup, 400 grains of the fibrous salt, in a temperature below 300°. It quickly became fluid, and slowly gave out its water without any ebullition, or liberation of gas. When it was become perfectly dry, it had lost 33 grains. I suspected, that in this experiment some of the salt had been carried off with the water; to determine this, I introduced into a small glass retort, 460 grains of fibrous salt; it was kept at a heat below 320°, in communication with a mercurial apparatus, in a regulated air-furnace, till it was perfectly dry: it had lost 23 grains. No gas, except the common air of the retort came over, and the fluid collected had but a faint taste of nitrate of ammoniac.

Though in this experiment I had removed all the fluid retained in the neck of the retort, still a few drops remained in the head, and on the sides, which I could not obtain. It was of importance to me to be accurately acquainted with the composition of the compact salt, and for that reason I compared these analytical experiments with a synthetical one.

I saturated 200 grains of solution of ammoniac, of,9056 with acid, ascertained the specific gravity of the solution, evaporated it at 212°, and fused and dried it at about 300°-260°. It gave 246 grains of salt, and a solution made of the same specific gravity as that evaporated, indicated a loss of 9 grains. Consequently, 255 grains of this salt contain 50,5 grains alkali, 100 grains acid, and 14,5 grains water.

We may then conclude, that 100 parts of compact nitrate of ammoniac contain 74,5 acid, 19,8 alkali, and 5,7 water.

V. _Decomposition of Carbonate of Ammoniac by Nitric Acid._

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.