Mention may be made here of cyanuric acid, H3C3N303, which contains the same ring system as the cyanidines.
Graham's work was developed by Liebig, who called into service many organic acids - citric, tartaric, cyanuric, comenic and meconic - and showed that these resembled phosphoric acid; and he established as the criterion of polybasicity the existence of compound salts with different metallic oxides.
One of the earliest, if not the earliest, was the investigation, published in 1830, which proved the polymerism of cyanic and cyanuric acid, but the most famous were those on the oil of bitter almonds (benzaldehyde) and the radicle benzoyl (1832), and on uric acid (1837), which are of fundamental importance in the history of organic chemistry.
There are polymers which have hardly any inter-relations other than identity in composition; on the other hand, there are others which are related by the possibility of mutual transformation; examples of this kind are cyanic acid (Cnoh) and cyanuric acid (Cnoh) 3, the latter being a solid which readily transforms into the former on heating as an easily condensable vapour; the reverse transformation may also be realized; and the polymers methylene oxide (CH 2 O) and trioxymethylene (CH20)3.
When heated above its melting-point, it yields ammonia, cyanuric acid, biuret and ammelide.