'■*!■• I Hall-Goodspevd : ( 'h rijsil 223 



mill material. In fact, however, these two analyses were in most cases 

 approximately the same and this result is assumed to depend upon 

 the fact tluit the finer division of the product of the pebble mill allows 

 tlie extraction of 2 per cent more rubber than was possible in the 

 case of the coarser product of the coffee mill. 



With these facts in miiul we decided to make the final grinding 

 of all our samples in tlie coffee mill since the matter of removing the 

 rubber adhering to the pebbles of the pebble mill is somewhat difficult 

 and time-consuming. This was done as a matter of practicability not- 

 withstanding the knowledge that the results would be too low to 

 express the actual percentages present. The discrepancy, liowev(M', 

 cannot be anywhere near the 2 per cent mentioned since tliat referred 

 to a plant in which the rubber content is much higher than the average, 

 and one moreover in which the very resinous material adhered to the 

 pebbles more persistenth' than in most cases. It is believed that the 

 amount of rubber remaining in samples of Chrysothamnus nauseosus 

 after grinding in a coffee mill and extracting by our method seldom 

 if ever api^roaches 1 per cent of the original sample. 



In a preliminary way, at least, we have obtained evidence as to the 

 effect of storage of the ground material upon rubber content. At 

 the start of our investigations it was assumed that if for any reason a 

 plant was not analyzed almost immediately after collection a deteriora- 

 tion in content and quality of the contained rubber would soon render 

 the result of its anah'sis of doubtful value. Undoubtedly the exposure 

 of shrub to drj'ing and weathering out of doors will bring about such 

 deterioration in the course of time (cf. Lloj'd, I.e., p. 10). As has 

 been noted above (p. 220) it is difficult so to divide a plant for analysis 

 that the halves or apparently equivalent portions will give closely 

 corresponding analyses. For this reason we did not attempt, in 

 seeking evidence as to the influence of storage upon rubber content, 

 to analyze a portion of a plant and after subsequent storage for some 

 months analyze an apparently e(iuivalent portion represented by the 

 remainder of the same plant. Kather the residue, after the first 

 analysis, of the ground material of a plant was stored in a stoppered 

 bottle and analyzed after a time. We have assumed that the amount 

 of deterioration in sucli a finely ground sample after storage approxi- 

 mates that which might be expected to occur within tlie tissues of 

 an entire plant after a corresponding period of time. The table whicli 

 follows details the results of a number of analyses of ground material 

 shortly after the original dates of collection and after periods of 

 storage varying from five to ten months. 



