MECHANICS AND USEFUL ARTS. 25 



actuated by a ratchet wheel and pawl ; and thus the strength of the 

 blow of the chisel is regulated to the varying breadth of the file. A 

 projection at the other end of the slide comes in contact with a cam 

 upon the driving shaft of the machine, and so sets the machine in mo- 

 tion. The blank to be cut is placed upon a travelling slide, .resting 

 upon a semicircular bed, which is mounted in trunnions resting upon 

 swivelling journals, so that the surface of the blank can be presented 

 at the desired angle to the chisel. The blank is held parallel to the 

 edge of the chisel by means of a weighted " leveller." All being 

 ready, the file is fixed in the bed, the machine is set in motion, and 

 presently the file runs out cut. The chisel makes from 800 to 1,500 

 cuts per minute, and will produce about five or six times the amount of 

 work which can be supplied by hand-cutting. A comparison of the 

 two modes of cutting hand and machinery, shows that, while a 

 machine, to cut fourteen-inch hard files, makes 1,000 cuts per minute, 

 or 600,000 cuts per day, a good file-cutter, upon the same size and 

 description, could only make 140 cuts per minute, or 84,000 per day. 



COPPER PAINT. 



A paint prepared by M. Oudry, of Paris, from electrotype copper re- 

 duced to an impalpable powder (by the aid of a steam-hammer), and 

 diffused in varnish, is, undoubtedly, a most important industrial discov- 

 ery. The preparation of the color is not difficult and not expensive. 

 It is stated to be susceptible of easy application to wood, plaster, cem- 

 ent, brass, or iron, and also to the hulls of ships. It forms a perfect 

 covering, dries rapidly, and takes an agreeable lustre susceptible of re- 

 ceiving, by means of chemical agents, the tone of bronze, bright or 

 dark, verd-antique, or Florence green, which has never before been 

 communicated to pure copper. Ornaments in brass or statues in plas- 

 ter, when painted in this manner, lose none of their most delicate de- 

 tails, and they assume completely the appearance of objects in bronze. 

 Even statues in plaster appear to resist remarkably inclement condi- 

 tions of the atmosphere. By mixing the powder of galvanoplastic cop- 

 per with certain fatty oils, Oudry obtained very beautiful greens of 

 varied hues. 



REPAIRING THE SILVERING OF LOOKING-GLASSES. 



The repairing of the silvering on the backs of looking-glasses has 

 hitherto been considered a very difficult operation. A new and very 

 simple method, however, has been described before the Polytechnic 

 Society of Leipsic. It is as follows : Clean the bare portion of the 

 glass by rubbing it gently with fine cotton, taking care to remove every 

 trace of dust and grease. If this cleaning be not done very carefully, 

 defects will appear around the place repaired. With the point of a 

 knife cut upon the back of another looking-glass, around a portion of 

 the silvering of the required form, but a little larger. Upon it place a 

 small drop of mercury : a drop the size of a pin's head will be sufficient 

 for a surface equal to the size of the nail. The mercury spreads imme- 

 diately, penetrates the amalgam to where it was cut off with the knife, 

 and the required piece may now be lifted and removed to the place to 

 be repaired. This is the most difficult part of the operation. Then 

 press lightly the renewed portion with cotton : it hardens almost inmae- 

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