106 THE MICROSCOPE. 



A CHEAP ROCK-CUTTING MACHINE. 



BY W. >". SHERMAN, M. D., MERCED, CAL. 



On page 86 (June number) appears an article on a new ma- 

 chine for grinding and cutting mineral sections, stating that 

 the price of the machine is $130. A description of a home- 

 made cheap apparatus, for the same purpose may be of inter- 

 est. While not so elaborate or complete, it answers an excel- 

 lent purpose. Storage cells are used. These consist of four 

 cells with five plates each, three positive and two negative. 

 The plates are made of sheet lead one-fourth inch thick, 7 

 by 8 inches with perforations, one-fourth inch apart. These 

 round holes are to be filled with the active material, composed 

 of the red oxide of lead for the positive and the yellow oxide 

 for the negative. The holes are threaded inside so as to firmly 

 retain the forming paste during charge and discharge. The 

 plates are connected together and placed in wooden cells which 

 are lined with an acid-proof paint, and have a neat cover or lid 

 over box, winch contains all four cells. The cells are about 

 150 amperes each, and are connected in series so that two, three, 

 or four cells may be used according to the power required. 

 These cells are charged by gravity cells and are receiving a 

 continuous current when not in use. They are connected to a 

 low resistance motor costing $15. It is one-eighth horse power 

 or eight volts, and runs at a rate of about 3,000 per minute. 

 It may rest upon a table or under a table, and is connected by 

 around leather belt to a small jewelers' lathe, which is arranged 

 for various wheels, for sawing / grinding or polishing. The drip 

 cups and pans, are easily improvised by the user. These same 

 cells can be used for various other purposes, and the motor 

 likewise. I use them for microscope lamps, dark rooms, for 

 surgical lamps, galvano-cautery, surgical engine, etc. The cost 

 of maintenance does not equal that of the Electric Light Co. 

 charges, and when not in constant use they are always fully 

 charged. The whole apparatus may be set up at a cost not to 

 exceed 875, and much cheaper, if cells and motor are all home- 

 made. The motor is portable, and can be used for ventilating 

 fan, static machine, and various other purposes. The speed is 

 controlled by a home-made foot rheostat, inserted in the bat- 

 tery circuit. Two storage cells of above size furnish sufficient 

 power for all my work, in grinding and polishing. 



