Pseudo-carbons are obtained as products of the action of various reagents upon the celluloses, and other of the so-called carbo-hydrates. These reagents, such as sulphuric acid, act in virtue of their dehydrating power; and the recognition of this fact, together with the supposed “carbonaceous” {25} character of the product, led to the erroneous conclusion that the carbohydrates are in such decompositions simply resolved into carbon and water; a conclusion which seems to derive additional warrant from the peculiar numerical relationship which exists between the C, H, O atoms of all the members of the group. Their relation is expressed in the general formula C_{n} H_{2(n−m)} O_{(n−m)}, and in the somewhat misleading term carbohydrate, which is applied to the whole group. We now know that the removal of water from these bodies by the action of dehydrating agents—including heat—follows the ascertained laws of chemical dehydration, involving molecular condensations and rearrangement, and that the pseudo-carbons are the extreme terms of a series of such condensations or cumulative resolutions. The matter, however, is not as yet sufficiently investigated to enable us to state with any preciseness the mechanism of these changes. Still this general statement will enable us to avoid many of the erroneous views which have existed on the subject, and in a measure to anticipate the results of future investigation.[6] [Footnote 6: It is worthy of mention that by the action of chlorine in presence of water, and by the action of concentrated nitric acid upon the cannel coals, substitution derivatives are formed resembling those obtained by the action of these reagents respectively upon the ligno-celluloses.]