86 



solid nitrocellulose absorbs camphor present in the liquid phase 

 (camphor and alcohol), forming a mass of gel cells enclosing a pseudo- 

 solution of nitrocellulose in camphor and alcohol. The subsequent 

 rupture of the cells during kneading and loss of alcohol by evaporation, 

 leads to an enormous increase in viscosity. There is, however, in the 

 case of camphor celluloid, no separation of suspensoid or solid phase, 

 such as may happen with some of the substitutes of camphor. This 

 is shown by miUdness or opacity in the celluloid, by brittleness and 

 lack of plasticity in the working. The plasticity of camphor 

 celluloid on heating to about 80° C. is attributed to the formation of 

 a liquid phase by fusion, diminishing internal friction. 

 , Dubosc admits that experimental evidence in support of these 

 views is meagre, but on the whole they appear reasonable. Exception 

 might be taken to regarding camphor as the dispersion medium when 

 it occupies only about one third of the bulk of the celluloid. 



Speculations on the structure of cellulose esters and the plastic 

 materials made from them inevitably lead to a consideration of the 

 structure of cellulose itself. Cellulose has already been treated by 

 other writers in these Reports^*, and a much-needed emphasis has 

 been placed on its colloidal character. There are stiU chemists \^'ho 

 write as if the elucidation of the structure of cellulose were a problem 

 analogous to the determination of the formula of, let us say, brucine 

 or dextrose. The underlying assumption appears to be that some 

 day the suflfix n in the formula (CgHjoOs) n will be determined, and 

 then, given a sufficiently large sheet of paper, the complete formula 

 will be constructed. It must be admitted that this assumption has 

 led to much interesting research^^. 



It is only natural that chemists should attempt to assign definite 

 molecular weights to the materials they handle. The teiidency 

 probably arises ultimately from the extraordinarj^ developments of 

 theoretical chemistry on the basis of Avogadro's hypothesis, culminating 

 in the work of Vant' HoflF. It may not be out of place to point out 

 that of aU the materials that we wear, handle and consume, those 

 to which the methods of Vant' Hoff can be applied are in a vast 

 minority. CoUoidal chemistry would be immensely simpUfied if it 

 could be brought under systematic mathematical treatment, but in 

 view of the vast differences in properties between the colloidal and 

 crystalline states, it is unreasonable to expect to force coUoids into 

 the crystalline system. It is agreed on aU hands that if cellulose and 

 similar colloids have a definite molecule, its weight must be extremely 

 large. But the larger the assembly of (CeHioOs) units becomes, the 

 more difficult it is to imagine what forces would come into play to 

 put a sudden stop to the j^rocess of aggregation. In view of the 

 continuous nature of plant growth, it is not to be expected that there 

 should be a definite limit to the size of the cellulose aggregate, any 

 more than there is to the size of a honeycomb. The hmit to the 

 aggregation of Cg units is probably set, not by internal chemical forces, 

 but by external conditions such as atmospheric temperature and 

 humidity, and the vital activity of the plant. — Index 14a. Wohler's 

 synthesis of urea was hailed as breaking down the barrier between 

 organic and inorganic chemistry, but crystalline substances like urea 



