H. F Lueders — Structure of Caoutchouc. 135 



Art. XIX. — Concerning the Structure of Caoutchouc ; by 

 Hermann F. Lueders/* 



AThile examining a number of specimens of crude rubber 

 from various regions, with regard to their impurities, my 

 attention was directed to the microscopic characters of the 

 rubber itself. The literature on the subject being scanty, it 

 appeared as if a brief examination of the matter might be 

 profitable. The following is a short summary of my results. 



Being unable to procure fresh stems of any rubber-produc- 

 ing plant, except Ficus elastica, the succeeding details con- 

 cerning the appearance and properties of the latex are taken 

 from that plant only. 



In Ficus elastica the caoutchouc is found in the copious 

 latex which is contained in relatively narrow, branching ves- 

 sels, abundant in the hypodermal and pith parenchyma. The 

 caoutchouc exists in the form of small, colorless globules on 

 the average S/i in diameter ; collected under oil of almonds 

 it retains the original appearance for some time; in about half 

 an hour the globules begin to coalesce, while at the same time, 

 solid particles separate out of the menstruum in which the 

 droplets are suspended. If the latex exudes in the air, the 

 coalescence of the globules is very rapid and, with the evap- 

 oration of the watery material, results in the speedy forma- 

 tion of a transparent film, soluble in chloroform, ether, benzole, 

 carbon disulphicle and similar solvents. 



There remains, however, an abundant white residue when 

 the dried latex is treated with any of the above solvents. This 

 residue consists of acicular or tabular crystals and grains. Its 

 behavior in presence of acids and other reagents, before and 

 after ignition, seems to indicate its identity with calcium 

 oxalate, while traces of starch are also found to be present. 



Faradayf found that a specimen of latex, brought in a 

 sealed bottle from South America, had an acid odor. It does 

 not appear from what plant the latex in question was derived, 

 nor whether its acidity was original or due to fermentation. 

 In Ficus the latex shows a weak alkaline reaction brought out 

 only by delicate indicators. The coalescence of the caoutchouc 

 globules under the influence of the air takes place quite 

 rapidly and completely so that the solidified latex rarely shows 

 any globules, nor have any of the specimens of crude rubber 

 in the Harvard Botanical Museum, which I had the privilege 



* Presented to the American Academy of Arts and Sciences, Boston, by- 

 Professor Goodale. 



f Quar. Jour, of Science, Literature and the Arts. xi. p. 15, quoted by Wiesner. 



