25 



70. Amateur's lapidary machine for slitting, grinding, 

 and polishing. Designed by J. B. Jordan. Price 121. 12s. 



1884. Exhibited by Cotton and Johnson. 



This consists of a mahogany framework similar to that of an 

 ordinary lathe, and is supplied with crank, heavy fly-wheel about 

 24 in. diameter and treadle occupying a floor space of 24 in. by 

 15 in. To the bed of this frame is fitted an iron casting bored to 

 receive two spindles, viz., a vertical spindle which carries the 

 slitting disc, grinding laps, &c., and another spindle to which is 

 fixed a horizontal plate carrying on its surface a cup containing 

 cement into which the material to be cut is embedded, and which 

 is retained and uniformly pressed against the slitting disc by 

 means of a cord attached to the plate near its edge, which, passing 

 over a pulley, supports a weight which gives a constant and 

 regular pressure. This plate can be raised or lowered as 

 required by means of a screw below the bearing. Horizontal 

 motion is given to the slitting disc by means of two 

 obliquely-set wheels below the bearing, over which the cord 

 passes to a horizontal wheel. When the machine is required 

 for grinding, &c., the slitting disc is removed and the laps, of 

 which three are provided, are fixed in its place. The whole of 

 the upper part is underlaid by a zinc tray, perforated in the 

 centre for the axles. At the side, on a movable ledge, stands a 

 water vessel with tap, by which the disc or lap can be kept 

 perpetually moistened. 



71. Apparatus used in grinding and mounting rock 

 sections for examination under a microscope. With 

 the apparatus is shown a series of slides in different 

 states of preparation. 



Lent by the Geological Laboratory, Royal College of 



1887. Science. 



These consist of emery of four degrees of fineness, the finest 



being previously washed ; Bunsen's burner, tripod, iron-plate, 



soap solution, Canada balsam, watch glasses, 1J in. squares of 



thick glass, glass slips, and round cover glasses. 



F. Apparatus used in Blowpipe Analysis. 



72. Letcher's blowpipe cabinet. Price, 34s. 



1886. Exhibited by J. Orme & Co., lateM. Jackson. 



As arranged for the Society of Arts, in a mahogany case. 



73. Letcher's blowpipe case. Price, 21s., in a box. 

 1880. Exhibited by T. H. $ J. T. Letcher. 



