CHEMICAL SELECTION OF MOTHEES. 89 



If two beets are represented by two regular cones, 

 K J H and L I G (Fig. 32), and in plan by two concen- 

 tric circles, it is evident that if an angle C A E he. 

 taken on the beet K J H, and another, B A D, on the 

 beet L I G, they will have the same opening, or 30 

 degrees. The section in each cone thus obtained bears 

 the same relation to the entire root. It becomes evi- 

 dent that if the slice taken is limited by the axis of the 

 beet, the sample will be one-twelfth of the entire root, 

 a result which could be obtained by cutting the beet in 

 two, then again into halves, etc. The practical work- 

 ing of the rasp is better understood by examining the 

 apparatus shown in the engraving (Fig. 33 ) 



The apparatus was at first a sort of circular saw, 

 but since has been considerably modified. The beet 

 is held in position by lateral knives, in such a way as 

 to bring the limit of rotating blades exactly on the axis 

 of the root; the latter is pushed forward with one hand, 

 while the gear wheels are put in motion with the 

 other. For special purposes the opening of the rasp 

 may be regulated to suit the requirements. 



Experience has demonstrated that the pulp 

 obtained from this rasp has the same density as that 

 made by rasping half a beet by hand. To have accu- 

 racy in the analysis of one beet, it is found desirable 

 to turn the root over, so as to secure another sample 

 from the same beet; consequently, with this conical 

 rasp it is possible, not only to get an average sample 

 of pulp from a series of beets, but also of the same 

 beet. The dry pulp obtained should be thoroughly 

 mixed; if small lumps are found in the mass these 

 should be taken out and finely chopped. The rasp, after 

 being used, must be brushed off, not washed with 

 water. It is interesting to note that the circular disk 

 was originally bronze, but is now constructed entirely 

 of steel; its surface is not unlike a coarse file used for 

 wood. A velocity of 400 to 500 revolutions per minute 

 is obtained without difficulty. 



