METHODS EMPLOYED. 13 



below. From 12 to 24 hours of such drying at 40° to 50° C. was found 

 to be sufficient for most samples. High temperatures were avoided, 

 because of their tendency to convert the caoutchouc into resins or 

 other products of oxidation. The moisture still remaining, although 

 slight, was determined in most cases by the usual methods, and the 

 final analyses were computed upon the basis of absolutely dry material. 

 The few exceptions are indicated in the tables. 



The leaves and stems of most samples were separated after drying, 

 since it was early found that they were not equally rich in rubber, and 

 that separate analyses were therefore desirable. The removal of the 

 leaves before drjdng would have resulted in the loss of latex through 

 bleeding. Leaves and stems were then ground separately in coffee 

 mills, until nearly all of the material would pass through a 30-mesh 

 brass sieve, i. e., one with apertures 0.0195 inch in diameter. It was 

 found desirable to include with the finely ground sample a very small 

 amount ground to pass only a 20-mesh or 10-mesh sieve (i. e., with aper- 

 tures of 0.0335 or of 0.0799 inch), since otherwise the sample would 

 pack too tightly in the extractors and clog the entrance to the siphons. 



Chemical Analysis. 



The acetone-benzene method of extraction was used, the practice 

 being essentially that described by Hall and Goodspeed (1919, p. 

 216) in their work on chrysil. The Bailey-Walker extraction ap- 

 paratus was used, because of its simple construction, efficiency as 

 an extractor, and the ease with which the parts could be cleaned. 

 The usual method was modified through the introduction into the 

 bottom of the extraction thimble of a thin layer of cotton, with two 

 disks of filter paper above it. About 5 grams of the thoroughly mixed 

 and ground plant material, taken from a weighing bottle with aid of a 

 spatula, were then added. This filled the thimble for about two-thirds 

 of the way to the top. A second thin layer of cotton was placed on top 

 of the sample to prevent danger of an overflow of the material into the 

 extraction flask. The extraction itself consists of two parts, as follows: 



(a) Extraction with 10 c. c. of boiling acetone for 3 hours on a 

 water-bath. This period was determined upon after it had been found 

 by experiment that all of the acetone-extractable substances came 

 over within the three-hour limit. The first portion of the extract 

 siphoned over is usually bright green in color. This is due to the 

 chlorophyll, which is very readily soluble in acetone. If the siphon 

 is working properly the chlorophyll will soon be completely dissolved 

 from the ground material and the acetone extract, as it passes through 

 the siphon, will be perfectly clear. At the close of the three-hour 

 period the thimble was removed from the flask with blunt forceps 

 and the acetone evaporated in a water- jacketed drying-oven. The 

 excess acetone in the flask was distilled and the residue dried for 

 4 hours in the oven, after which it was cooled in a desiccator and 

 weighed. This residue is assumed to contain all of the chlorophyll, 



