ON WAVE-LENGTH TABLES OF THE SPECTRA OF THE ELEMENTS. 227 



Palladium — continued. 



On the Present Position of the Chemistry of the Gums. 

 By H. H. Robinson, M.A., F.C.S., F.I.C. 



The gums are a class of substances characterised by the property of either 

 dissolving in water to form viscid solutions, or of absorbing water to form 

 gelatinous pastes ; these solutions or pastes, on exposure to air, lose their 

 water, and dry to hard, translucent, somewhat glassy masses. The gums 

 are uncrystallisable, and are composed of carbon, hydrogen, and oxygen. 

 As found in nature they contain more or less ash constituents, and 

 sometimes contain a little nitrogen. The nitrogen, if present, is small 

 in amount, and is not regarded as an essential component, and this 

 differentiates them from gelatin, glues and proteids, which also possess the 

 above properties, but contain a considerable proportion of nitrogen. 



The gums occur in plants, and are often found as exudations on the 

 bark or other surfaces ; some gums have also been found in animal 

 products. Different views have been held as to the processes by which 

 gum is formed in the plant. One view considers the production of gum 

 part of the normal metabolism of the plant ; in the case of tree gums 

 they are generally regarded as an excretion resulting from the breaking 

 down of cell tissue. In certain cases the formation has been attributed 

 to the action of a fungus, which attacks the tree and generates an enzyme 

 that penetrates the tissues and transforms the cell walls, (fee, into aum. 

 A third view attributes it to bacterial action, and it is claimed that 

 specific bacteria have been found capable of producing different kinds of 

 gum. The employment of a system of inoculating the trees to cause the 

 production of gum has been suggested, but the evidence in support of it 

 is as yet very slight. 



The word 'gum' in its earliest use was probably applied to plant 



Q2 



