His method of investigation consisted in (1) estimating {43} the cellulose; (2) determining the loss sustained by the fibre when boiled for 5 minutes, and also for 60 minutes, with an alkaline solution (caustic soda 1 per cent. Na_{2}O), the former being taken to represent the purely solvent action, the difference between the two amounts being an indication of the _degrading_ action of the soda; (3) determining the ultimate composition (C H and O) of the fibre substance. It should be observed that the specimens were carefully averaged and purified by boiling in glacial acetic acid and in alcohol. On carefully considering the following table it will be seen that the chief points brought out by Webster’s investigation are (1) the association of a low carbon percentage with pectous properties and considerable degrading action on long boiling in alkali. The bearing of this will be better understood in connection with a discussion of the properties of pectic acid (p. 28) and the oxycelluloses (p. 13). (2.) The influence of the composition of the original fibre on the isolated cellulose. The solutions of aniline sulphate and of the aniline colours give valuable aid in a diagnosis of plant substances. Webster observed, as was to be expected, that the yellow colour produced could be taken as an indication of the amount of lignification, those fibres which were of a pectous nature showing little or no colour. On the other hand, when the fibres were treated with a neutral solution of the so-called alkali-blue it was found that the converse took place, highly pectous fibres being dyed much more deeply than those which were lignified. (Compare the action of aniline colours on oxycellulose, p. 11.) If the student require more precise knowledge of the nature of a fibrous material than that afforded by a determination of the cellulose, the following method of analysis will prove of service. {44}