82 REPORTS ON THE STATE OF SCIENCE.—1917. 
Hemicelluloses from seeds are employed in the manufacture of sizing 
materials (P. C. D. Castle, Eng. Pat. 10,822, 1905, C. V. Greenwood, 
Eng. Pat. 564, 1912). The hemicelluloses, no doubt, vary in composition, 
but that from the locust-bean (Ceretonia siliqua) consists of a complex 
of mannan and galactan in the proportion of about 2: 1, mannose and 
galactose in these proportions being the products of hydrolysis (Bourquelot 
and Herissy, ‘ Compt. Rend.’ 1889, 129, 228, 231, also 1889, 129, 391-398). 
Solutions of hemicelluloses of this type yield, on evaporation, clear trans- 
parent continuous films which have considerable tensile strength and 
are much tougher than films of nitrocellulose. In composition they 
approximate to the formula C,H,,0; (H. B. Stocks and H. G. White, 
‘Jour. Soc. Chem. Ind.’ 1903, 4, also C.F. Cross, ‘ Lectures on Cellulose, 
Inst. of Chem.’ 1912). They contain but little mineral matter and are 
not acidic in character. Sols of the hemicelluloses show a very high 
viscosity, increasing enormously with the concentration, but heat has 
only a slight effect in decreasing it. Dilute acids lower the viscosity 
very considerably, especially the mineral acids; alkalies increase the 
viscosity, especially of strong sols, which become glutinous or tenacious. 
Salts generally have very little effect except in strong solutions, in which 
case the complex is in many cases precipitated. Iron and copper salts, 
hydrogen peroxide, sodium peroxide, and potassium persulphate all 
lower the viscosity of the product. Heating under pressure and with 
organic acids renders the material quite fluid (C. V. Greenwood, Eng. 
Pat. 569, 1908), but partial reversion takes place after a time. 
Hemicelluloses form adsorption. compounds with bases such as Ba(OH), 
and Ca(OH), becoming more or less solidified and in diluted sol precipitated. 
Basic lead acetate forms a heavy solid white opaque gel, KMnO, and 
Fehling’s solution also forms solid gels. Boric acid renders the gel more 
viscous, while the action is still more marked with borax, a solution of 
the complex being solidified to a brittle gel, while even in very dilute 
solution the material becomes so viscous that it ceases to flow and also 
does not wet the containing vessel. The mixing of viscous gels of this 
type with water is an interesting proposition ; the surface tension is so high 
that water will not penetrate. On stirring, the gel breaks up into small 
particles, which by long-continued stirring gradually absorb the water 
and coalesce, the mixture becoming homogeneous again. Friction is 
a considerable factor in the mixing, but, as dilution proceeds, the surface 
tension being progressively lowered, mixing becomes more and more 
easy. If the material is added to a large volume of water it is practi- 
cally impossible to obtain a homogeneous solution. Mixtures of hemi- 
celluloses with starch paste, some soluble starches, dextrin, if not too 
concentrated, Irish moss mucilage, and agar mucilage are easy to prepare, 
and homogeneous probably because the surface tensions are equal or nearly 
so; but with hemicelluloses and gum arabic, gelatin, and strong solutions 
of dextrin the interfacial pressure must be considerable as there is no 
interpenetration, and although vigorously agitated they form granular 
or frothy heterogeneous mixtures which sooner or later separate into 
two layers of the different materials. The reason for this difference is 
not very apparent. 
The hemicelluloses, consisting of mannan and galactan, react with 
tannic acid to form complexes, which in presence of excess of tannic 
acid appear as an opaque turbid sol with considerable reduction in 
