ON AMMONIA.
The constitution of ammonia still remains undecided. The latest experiments on this article are those of Dr. Henry, in his essay on the analysis of the compounds of nitrogen. (Memoirs of the Manchester Society, vol. 4, 1824.) By electrifying ammoniacal gas over mercury, as carefully as could be devised, Dr. Henry found results as under:
| 1st | experiment | 44 | measures became | 88+ |
| 2d | 157 | 320 | ||
| 3d | 60 | 122 | ||
| 4th | 120 | 240 |
The evolved gases carefully analysed by combustion with oxygen, were found to consist of 3 volumes of hydrogen and 1 of azote. The analysis of ammonia was also effected by exploding it with nitrous oxide, with the requisite precautions. The results confirmed the previous ones by electricity, both in regard to doubling the volume of ammonia, and establishing the ratio of 3 to 1 in the volume of hydrogen and azote.—These experiments are highly interesting as far as regards the question of ammonia, as they exhibit the latest investigations of one who has previously shewn uncommon skill and perseverance in this kind of analysis. (See Philos. Transact. 1809, &c.)
Dr. Henry’s analysis of ammonia, in 1809, has been adverted to in our article on the subject, vol. 1, page 429. The results of that Essay are given in a tabular form; and the mean of six experiments was nearly as we have stated, namely, that ammonia consists of 27¼ measures of azote, and 72¾ hydrogen. To this it may be proper to add, that the two extremes were, 26.1 azote and 73.9 hydrogen, and 28.2 azote with 71.8 hydrogen; also that a small error has crept into the table, which being corrected, the average results are reduced to 27 and 73, very nearly. Subsequently, both Dr. Henry and Sir H. Davy concurred in assigning 26 and 74 for the most approximating numbers. (See Nicholson’s Journal, 25, page 153). The true quantity of gases procured by the decomposition of ammoniacal gas by electricity, was concluded by both these authorities, to be 180 for each 100 of ammonia, when the requisite precautions were taken, as we have related in vol. 1.
From what is stated above, it is evident the subject is one which requires extraordinary skill and attention. This I can attest from my own experience, which has been frequently renewed and varied; but the results have not been sufficiently accordant to yield me satisfaction.
About ten years ago, I made several experiments on the decomposition of ammonia, which, though they are not convincing, deserve, perhaps, to be recorded in their results.—Some more recent experiments are incorporated with them.
Decomposition of ammonia by nitrous oxide.—I made many experiments, by exploding mixtures of nitrous oxide and ammoniacal gases over mercury. The excess of gas was mostly on the side of ammonia, but the proportions were varied in the different experiments, from 10 vol. nitrous oxide to 11 ammonia or to 5, which are about the extremes capable of being fired by the electric spark.
When 10 parts nitrous oxide and 5 of ammonia are exploded over mercury, the residuary gas contains some free oxygen and some nitrous acid derived from the decomposition of the excess of nitrous oxide used; with 6 parts of ammonia there is rarely any free oxygen. When 10 parts of nitrous oxide, and 7 of ammonia are fired, I never found any free oxygen or hydrogen; but when the ammonia is at or near 8 parts, I find from ¹/₂₀ to ⅒ of the hydrogen from the ammonia in the residuary gases. The two gases appear to be completely decomposed; the oxygen of the nitrous oxide, as far as it can, unites with the hydrogen of the ammonia, without forming any portion of nitrous acid or of free oxygen, and the residue contains the azote of both gases, and the unburnt hydrogen from the ammonia, as Dr. Henry first observed. This continues to be the case till the ammonia becomes 11 parts, when the hydrogen amounts to about ⅓ of the whole quantity which the ammonia yields.
From the above it would seem that the proportions for mutual saturation must be 10 nitrous oxide with from 7 to 8 parts of ammonia. This agrees with the deduction in Dr. Henry’s first essay that 13 nitrous oxide require 10 of ammonia; or that 10 require 7.7: but according to the theory of volumes 10 would require 6⅔; and Dr. Henry recommends in his late essay 10 nitrous oxide to 7.7 or 8⅓ parts of ammonia, in order to secure a small excess of the last, and consequently some free hydrogen after the explosion. The former of these proportions would have nearly ⅐ of the residue hydrogen, and the latter nearly ⅕, supposing the gases pure originally. This gives more hydrogen than I have ever found; but the azote in my experience nearly agrees with the doctrine of multiple volumes.
Decomposition of ammonia by nitrous gas.—About 30 experiments carefully made on mixtures of nitrous gas and ammoniacal gas gave very discordant results. At one time 10 parts nitrous gas with 14 ammonia gave ⅓ of hydrogen in excess, and another time 10 nitrous with 12 ammonia gave excess of hydrogen = ⁹/₂₀; generally 10 parts with 6 or less gave oxygen, and 10 with 8 or more gave hydrogen in the residue.
Decomposition of ammonia by oxygen.—The limiting proportions of oxygen and ammonia which I have fired, are 10 oxygen to 4 ammonia for the minimum, and 10 oxygen to 22 ammonia for the maximum. When 10 oxygen were fired with 4 ammonia, there were ²⁵/₃₇ of the oxygen left, and there was a deficiency of azote amounting to ¹/₁₂ of what was expected from the ammonia, owing no doubt to nitrous acid generated by the explosion. When 10 oxygen to 1.8, or from that to 2.2 ammonia are used, there is a surplus of about ¼ or ⅓ of the hydrogen contained in the ammonia, left in the residue of the gas. When the ammonia is between 13 and 14 there is usually a trace of oxygen or hydrogen as it approaches either of these limits. By the theory of volumes, 10 oxygen should saturate 13⅓ of ammoniacal gas. I have not any instance of hydrogen being left when 14 ammonia were used, though there ought to be ¹/₂₀ of the whole left; and much smaller quantities than that are appreciable by well known methods. The azote resulting from the decomposition of ammonia is usually very nearly ½ the volume of the ammonia.
On the whole the results from firing ammonia and oxygen gas appear to me more satisfactory than those obtained from nitrous oxide and nitrous gas, as they are more simple and less perplexed with any theoretic views.
It may be proper to remind the reader that when we speak of 10 parts of one gas uniting with 8, 10, or more, of another in the above and other cases, it is to be understood of gases absolutely pure; not that we ever obtain them in that state, but approximating as near as we can to it, we mix given portions of such gases as we can obtain, and then in our calculations of results deduct for the impurities.
One source of uncertainty in these experiments on firing mixtures of ammonia, is that the real quantity of ammoniacal gas operated upon is not known. If a certain measure of ammonia be transferred through mercury ever so dry, some portion of it gets entangled in the mercury, and 100 measures become perhaps 95: now in the explosion it is a question whether any part of the 5 measures absorbed is decomposed. I have marked this attentively, and am persuaded that generally speaking, little if any of that portion is decomposed; but some trace of it appears mostly afterwards in the residue as it is liberated from the pressure of its own kind of gas, and hence easily rises into the gaseous mixture. Notwithstanding, when the loss of gas by transfer amounts to 10 or 20 per cent., I have reason to believe that some part of it suffers combustion occasionally.
Volume of gases from the decomposition of ammonia.—It has been observed (vol. 1. Ammonia) that Sir H. Davy obtained 180 measures of gases, by means of electricity, from 100 of ammonia as the maximum when the operation was performed with great care, and Dr. Henry in like circumstances, produced 181, whilst I found 187 measures; since that, as has been related, Dr. Henry has found 200 measures. It is not easy to account for these differences; I am inclined to the opinion that the volume of gases is very nearly doubled, but probably rather less than more. I find the experiments on the rapid combustion of ammonia agree best with that opinion.
Decomposition of ammonia by a red heat.—A short time since I repeated the decomposition of ammonia by passing the gas through a red hot copper tube. The proportion of azote to hydrogen, due allowance being made for a minute portion of atmospheric air, was upon the average of a number of experiments, 26 of the former to 74 of the latter.
Decomposition of ammonia by oxymuriatic acid.—I have made several experiments on this mode of decomposition since the results published in vol. 1, page 435. It is well known that a solution of oxymuriate of lime decomposes ammoniacal salts; water and muriatic acid are produced, azote liberated, and the acid previously combined with the ammonia is evolved. But this is not all; an excessively pungent gas or perhaps vapour is produced, exciting sneezing, and inducing catarrh; the constitution of this vapour is not well understood; it is never formed, as far as I know, without the presence of both oxymuriatic acid and ammonia. The results of such mixtures are of course complicated and likely to be unsatisfactory; it may notwithstanding be useful to relate some of them.
When clear oxymuriate of lime solution, and a salt of ammonia are mixed together with a little excess of oxymuriate, the ammonia is mostly decomposed, the oxymuriate being converted into muriate of lime by the hydrogen of the ammonia, whilst the azote is evolved, and the acid previously combined with the ammonia is liberated; hence oxymuriatic acid gas is also liberated along with the azote; and it is required to be taken out before the azote can be estimated. This circumstance may be obviated by previously adding the requisite quantity of pure potash or soda, to engage the acid, or by leaving a little undissolved lime in the oxymuriatic solution. I could never obtain a volume of azote equal to half that of the ammonia (supposed to be in a gaseous state) though it is universally allowed not to be less than that, if the whole of the azote be evolved; on one occasion only I got so much as ¹⁴/₁₅ of that quantity. The residue of liquid has the extremely pungent smell; but the azotic gas after passing through pure water has no smell. When this experiment is made over mercury, the oxymuriatic acid acts upon it, and hence the excess of oxymuriate should be such as to leave a portion of that undecomposed at the conclusion.
When the object is to ascertain the hydrogen in ammonia, a portion of salt known to contain a given weight of ammonia is to be treated with oxymuriate of lime solution, the strength of which is accurately determined by means of green sulphate of iron, or otherwise. The ammoniacal salt in solution is then to be mixed with a moderate redundance of the oxymuriate liquid, and with a few drops of caustic potash, and the mixture must be repeatedly agitated for some time. At length the liquid must be tested by the green sulphate of iron, and hence the quantity of acid spent upon the ammonia will be determined. I have mostly found the hydrogen this way below the common estimate, allowing the ammoniacal salts to be correctly determined.