34 SECTIONAL ADDRESSES. 



Similar reactions are impossible with acetyl or benzoyl derivatives 

 of sugars owing to the ease with which the substituting groups are 

 eliminated. In order to illustrate the utility of methylation in deter- 

 mining stiiicture, we may ascribe to any sugar derivative the general 

 formula S — G, where S is a sugar residue and G the gi'oup with which 

 it; is condensed. Complete methylation may be effected, according to 

 the solubilities involved, by silver oxide and methyl iodide or, alterna- 

 tively, by methyl sulphate and alkali. The compound obtained will 

 yield, on hydrolysis, at least two products, one of which is a methylated 

 sugar. Determination of the number and distribution of the methyl 

 groups in each of the cleavage products gives the stiucture of the pai'enfc 

 compound, as the mode of attachment of the constituents is thereby 

 known. 



In the sjiecial case where the group G is also a sugar residue the 

 general formula of the complex may be written S — Sj. The compound 

 would thus be a disaccharide, and precisely the same structural study 

 can be applied to it. The method is equally applicable to trisaccharides, 

 S — Sj — Sj, and finally to polysaccharides S S„. 



The development of this line of research has demanded the prepara- 

 tion of a large variety of methylated sugars, which play the part of 

 reference compounds in that the position of the alkyl gi'oups in them 

 is known. 



As I wish to deal particularly with the constitutional problems of 

 polysaccharides, I shall make no attempt to sununarise the results wliich 

 have been obtained in the study of the simple sugars, the glucosides, 

 or the disaccharides, but turn at once to the case presented by cellulose. 



Cellulose. 



(With Dr. W. S. Denham arid Dr. E. L. Hirst.) 



The extensive literature which has grown up on the constitution of 

 cellulose affords little satisfaction to the organic chemist. Despite the 

 complications involved and the many liabilities to error, it seems 

 impossible for workers on cellulose to resist the temptation tO' ascribe 

 a molecular formula to the compound. The difficulties which stand in 

 the way are too numerous to mention, but the m.arked stability of 

 cellulose under some conditions and its curious reactivity under others, 

 coupled with its limited solubility and lack of volatility, are outstanding 

 obstacles. As a result, many divergent and even conflicting suggestions 

 have been put forward to represent the polysacchaiide stiaicturally, 

 and the views of chemists both within and without the large circle 

 of workers in this field are chaotic. The confusion is increasefl by 

 the fact that many fommlas for the compound are published in haste 

 to be corrected at leisure, and this unhappy state of affairs was never 

 more pronounced than to-day. I would refer you to an article by Hans 

 Pringsheim,' in which he classifies the nientality of investigators and 

 puts forward a plea that, if sure progress is to be made, the chemistry 

 of polysaccharides must be pursued slowly step by step. Impetuous 

 and hastv theorising does infinite hann. 



The first essential in arriving at a satisfactory formula for cellulose 



