RICE PAPER, a name very improperly applied to a beautiful white and soft vegetable membrane, belong ing to the bread fruit tree, the Artocarpus incisifolia of Linnet's.
The following observations on its structure, made by Dr. Brewster, are taken from the Edinburgh Journal of Science, No 3, to which the reader is referred for a drawing of the structure.
"The substance commonly known by the name of Rice Paper is brought from China in small pieces, about two inches square, and tinged with various colours. It has been for some time used as an excellent substitute for drawing paper, in the representation of richly colour ed insects, and other objects of natural history, and has been employed in this city with still more success in the manufacture of artificial flowers.
"Although rice paper has a general resemblance to a substance formed by art, yet a very slight examination of it with the microscope is sufficient to indicate a vege table organization. In order to observe and trace the nature of its structure, it was necessary to give it some degree of transparency ; and I expected to ac complish this by the usual process of immersing it in water or in oil of the same refractive power. This operation, however, instead of increasing the transpa rency rendered the film more opaque, and suggested the probability that, like Tabasheer, it was filled with air; and that the augmentation of its opacity arose, as in the case of that siliceous concretion, front the partial absorp tion of the fluid.
"In order to expel the air from the cells in which it seemed to be lodged, I exposed a piece of the rice paper to the influence of boiling olive oil. The heat immedi ately drove the air in small bubbles from the cells near the margin ; but it was with some difficulty that it was forced to quit the interior parts of tho film. As
the olive oil had now taken the place of the air, and filled all the cells, the film became perfectly transparent, and displayed its vesicular structure when placed under a powerful microscope.
"It will appear from the drawing executed by Mr. Greville, that the rice paper consists of long hexagonal cells, whose length is parallel to the surface of the film ; that these cells are filled with air, when the film is in its usual state; and that from this circumstance it de 'rives that pccriliar softness which renders it so well adapted for the purposes to which it is applied. When the film is exposed to polarised light, the longitudinal septa of the cells depolarise the light like other veget able membranes.
" Among the three specimens of rice paper which I have produced, there is one from which all the air has been expelled by the boiling oil; another in which some of the air bubbles still appear in the vesicles, the air having been only partially expelled by boiling water ; and a third which is in contact with water without having been deprived of any of its air bubbles.
"Upon mentioning to Mr. Neill the preceding expe riments, he informed me that the lady in Edinburgh, Miss Jack, who had employed rice paper with such success in the manufacture of artificial flowers, had learned from her brother, who was in China, that it was a membrane of the bread fruit tree, the ?rtocarj:us incisifolia of naturalists.