In a recent small note in Volume III of these Annalen I stated that reaction of cyanogen with ammonia solution gives, in addition to several other products, oxalic acid and a crystalline, white substance, which latter was determined not to be ammonium cyanate, although one always obtains it in attempting, for example by a so-called double decomposition, to unite cyanic acid with ammonia. The fact that in combining, these substances seem to change their nature and a new substance is thus formed directed my renewed attention to this matter, and this investigation has yielded an unanticipated result that reaction of cyanic acid with ammonia gives urea, a noteworthy result in as much as it provides an example of the artificial production of an organic, indeed a so-called animal, substance from inorganic substances.

I have previously stated that one obtains the above mentioned crystalline, white substance best by decomposing silver cyanate with ammonium chloride solution or lead cyanate with ammonia solution. By the latter method I have prepared a not insignificant amount of it for use in this investigation. I obtained it in colorless, clear, often more than inch-long crystals, which formed narrow, right-angled, four-sided prisms without appreciable tapering.

With caustic potash or lime this substance evolved no trace of ammonia, with acids it showed absolutely none of the ready decomposition phenomena of cyanate salts, namely evolution of carbonic and cyanic acids and it even failed to give lead and silver salts as true cyanate salts do; it can thus contain neither cyanic acid nor ammonia as such. Since I found that the last mentioned method of preparation gives no by-products and that lead oxide separates pure, I imagined that in the union of cyanic acid and ammonia there might be formed an organic substance, perhaps even a substance analogous to the vegetable salt-forming bases; from this point of view I planned several experiments on the behavior of acids with the crystalline substance. It was however inert to these with the exception of nitric acid, which in a concentrated solution of this substance formed a precipitate of brilliant crystal flakes. After purification by repeated recrystallization, these crystals displayed a decidedly acidic character, and I was already inclined to consider them as a specific acid, when I found that they gave nitrate salts on neutralization with bases from which the crystalline material could be recovered with alcohol with all the properties it had before reaction with nitric acid.

This similarity in behavior to urea led me to conduct analogous experiments with fully pure urea isolated from urine, with the completely unambiguous result that urea and this crystalline substance, or ammonium cyanate if we could call it so, are fully identical substances.

I mention the behavior of this artificial urea no further since it agrees completely with reports in the literature on urine-urea from Proust, Prout and others, and I note only the fact they did not report, that on distillation the urine-urea, like the artificial, besides giving a large quantity of ammonium carbonate, also evolved a striking amount of the pungent odor of cyanic acid analogous to that of acetic acid, just as I have found previously during distillation of mercury cyanate or uric acid and especially uric acid mercuric oxide. During this distillation of urea there forms at the same time another white, apparently specific substance, which I am now occupied with investigating.

If mixing cyanic acid with ammonia really gives only urea, then urea must have the same composition as one finds through calculation for ammonium cyanate according to the constitutional formula I have given for cyanate salts; and this is in fact the case, if one assumes one atom of water, as all ammonium salts contain water, and considers Prout's the best analysis of urea. According to him^* urea consists of:

Ammonium cyanate would consist of 56.92 cyanic acid, 28.14 ammonia, and 14.74 water which means for the isolated elements:

Thus had one not found formation of urea from cyanic acid and ammonia as in the experiment, one could have calculated as above that ammonium cyanate with one atom of water would have the same constitution as urea. Burning cyanic acid over copper oxide yields 2 volumes of carbon dioxide and 1 volume of nitrogen, but burning ammonium cyanate should yield equal volumes of these gases, thus also the same ratio from burning urea, and in fact Prout has found this.

I refrain from all the considerations which so naturally suggest themselves from this fact, especially in respect to the composition ratios of organic substances and in respect to similar elemental and quantitative compositions among compounds with very different properties, as may be supposed, among others, of fulminic acid and cyanic acid and of a liquid hydrocarbon and the olefiant gas, and it must be left to further investigations of many similar cases to decide what general laws can be derived therefrom.

* ) Annals of Philosophy. Vol. XI. 1818, p. 354. [Original: Prout, W. Observations on the Nature of Some of the Proximate Principles of the Urine; with a few Remarks upon the Means of Preventing those Diseases Connected with a Morbid State of that Fluid, Medico-Chirurgical Transactions, VIII, Pt. 1, 1817, pp. 526-549]

** ) This is based on the new atomic weights of Berzelius: thus N = 88.518, C = 76.437, H = 6.2398, O = 100.000, water (H) = 112.479, ammonium cyanate = NH³ + CNO and urea = NH³+CNO+H· .

[Note: The original footnote (shown below)uses special symbols. The dot above the H atom denotes an oxygen and barred atoms are to be doubled. This notation derives from uncertainty about multiplicity in atomic weights, e.g. does an amount of nitrogen 88.518% of an amount of oxygen correspond to the same number of atoms, or twice (or half) as many? His formula for urea is thus N₂H₆+C₂N₂O+H₂O or altogether C₂H₈N₄O₂, which is double our CH₄N₂O.  His corresponding formula for ammonium cyanate, C₂H₆N₄O, seems to assume that water should be added to give the salt actually observed, a "hydrate".]

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Problems

By far the most powerful tool in the early development of organic chemistry was elemental analysis. Answering the following problems will help you understand some of the factors that were involved in this procedure. Nowadays various kinds of spectroscopy have largely replaced elemental analysis, but in general results from combustion analysis are still required for publishing reports of new compounds. This is among the most venerable, if not the most sensible, traditions in organic chemistry.

1. Compare the elemental percent composition of urea using modern atomic weights with Wöhler's values for theory and experiment. What do you notice?

2. How good are Berzelius's values for atomic weights?

3. Liebig and Wöhler found that salts of fulminic acid (HONC) and cyanic acid (HOCN) were isomeric. How accurate would elemental analyses have to be to reveal that "a liquid hydrocarbon" (say C₁₂H₂₆) and "the olefiant gas" (C₂H₄) are not isomeric? What if, by the liquid hydrocarbon Wöhler meant an olefin, such as butylene (C₄H₈)?

4. After consulting the page on Liebig's method of analysis, reconstruct how the elemental analysis of urea could have been done experimentally. (You need also to know that when heated with cupric oxide and copper many substances released their nitrogen as N₂ which could be measured by volume.) In light of this approach examine the theoretical and experimental results in Wöhler's paper carefully for errors in logic or arithmetic or both. What do you conclude?