APPAEATUS FOR HOLDING SPECIMENS 



65 



,1 



cone (G), whicli in its turn is driven from the motor. By shifting 

 the belt on the speed cone, a range of speeds varying from 

 about 300 to 1,000 revolutions per minute can be obtained. 



The disc B is made of brass, and fits, by means of a tapered 

 fitting, into the spindle A, which allows of its easy removal 

 and at the same time ensures accuracy in the running. 



A lip (E) projects downwards and prevents any grinding or 

 polishing material reaching the bearing. 



The cloth for polishing, or emery paper for grinding, is 

 secured to the disc by a simple but very effective device. A 

 groove (K) is made in the edge of the disc, and the paper or 

 cloth is stretched over the surface of the disc and is held in 

 position by means of a garter made of a stiff 

 brass spiral spring, which presses the material 

 into the groove. In this way the cloth, or paper, 

 is held in contact with the disc, no matter what 

 its thickness may be (see Fig. 68). 



In order to collect the spent polishing 

 materials, the disc is surrounded by a catcher 

 (C), which can be easily removed for cleaning. 

 In the top of the catcher is fitted a guard 

 ring (D) which, being wide, forms a rest for 

 the hand, and by being continued downwards 

 below the surface of the disc, and nearly touch- 

 ing the edge, prevents any specimens that are 

 being polished from falling into the catcher 

 should they be let slip from the fingers. 



This ring is also used for stretching the paper 

 or other material on the disc in the following 

 manner : 



The catcher (C) being removed, the paper or 

 material is placed on the disc (B) and the ring 

 (D) pressed over the paper until the ring (D) is 

 about half-way down the edge of the disc (B). 

 garter is stretched over the edge. The ring (D) is now pressed 

 right down over the disc, and the garter spring is pressed home 

 into the groove. 



If it is desired to remove a piece of paper that has been fitted 

 to the disc so as not to disturb the folds of the paper, the garter 

 spring should be removed downwards. The paper should be 

 replaced in the manner described above. . 



Should the disc at any time become so firmly nxed m 

 the spindle that it cannot be removed by hand, a pair of liftmg 

 levers are suppHed, which can be placed resting on the edge of 

 the catcher with one end under the disc ; a steady pressure on 

 the other end wiU raise the disc from its fitting in the spnidle 



A cover is provided to protect the revolving disc from dust 

 when it is not in use. 



Fig. 69. — 

 Pipettes. 



The spring 



