The chemical composition and behaviour of india-rubber are among the most difficult problems with which the organic chemist is confronted. The nature of these problems can only be indicated here in the barest outline. For further information the works of Weber and of Schidrowitz should be consulted. The latter gives references to the original chemical papers down to the end of 1910.

Technically pure rubber consists of crude commercial rubber which has been thoroughly washed and dried in vacuo. Much of the rubber produced on plantations is therefore already practically in this condition. The difficulties which stand in the way of the further study of this substance may be stated in the words of Weber:—" These difficulties are physical rather than chemical, that is to say they do not so much consist in the functional complexity of india-rubber as in the circumstance that these molecules are only known with the colloidal state superimposed upon them."