EECBEATIYE SCIENCE. 



277 



dallions of moderate size. The form Fiij. 2 

 is most easily obtained, but the form Fig. 

 3) is rather more convenient, as the open 



Fio. 2. 



Fig. 3. 



Fig. 4, 



mouth renders the interior more ready of 

 access, and offers greater facilities for obser- 

 vation. Suppose one of the latter obtained, 

 a piece of wood should now be fixed across it 

 by simple pressure, as at a (Fig. 4) ; the jar 

 may then be fiUed 

 to within an inch of 

 the top with a satu- 

 rated solution of 

 sulphate of copper, 

 and a few addi- 

 tional crystals may 

 then be thrown in, 

 to keep up the 

 strength of the li- 

 quid as copper is 

 deposited on the mould. Now prepare a 

 small bladder, or portion of a larger one, 

 of sufficient size to co- 

 ver the zinc-plate loose- 

 ly. Make a mixture of 

 one part sulphuric acid 

 and five parts water; 

 fill the membranous 

 bag with it, and tie it 

 over the zinc-plate, giv- 

 ing the whole of this 

 part of the apparatus 

 the form shown in Fig. 

 5. It may then be 

 applied to the deposi- 

 tion cell in such a 

 way that it shall rest on the beam (a, 



Fig. 5. 



Fig. 4) by the wire (w. Fig. 5), the coin 

 hanging on one side, and the covered zinc- 

 plate on the other. Both ought to be com- 

 pletely immersed in the solution of sulphate 

 of copper. If this part of the business is 

 carefully managed, and the mould is not put 

 into the solution till all is quite ready, accord- 

 ing to the instructions above given, the sur- 

 face will be instantaneously covered with a 

 thin film of copper, which will gradually in- 

 crease in thickness and tenacity for some 

 hours. After about four-and-twenty or thirty 

 hours, the mould may be removed from the 

 cell, and the copper from the mould, when all 

 the lines and impressions of the original 

 coin will be faithfully reproduced in the 

 copy. 



If, however, the copper has not been de- 

 posited on the mould, or has only been depo- 

 sited in part — and it is only fair to admit the 

 possibility of such a catastrophe at a first 

 attempt — the error must be sought out and 

 rectified. If no copper has been deposited, it 

 may probably be owing to the fact that the 

 connection between the wire and the zinc, 

 or between the wire and the mould, was 

 imperfect ; and the mode of correcting this 

 error is obvious. If copper is found to cover 

 a part of the mould, and not other parts, it 

 is most probably owing to the presence of 

 dirt or some foreign matter on the surface o f 

 the mould. In this case the deposited copper 

 should be removed, and the mould thoroughly 

 cleaned ; after which the process as above 

 detailed can be repeated. Should the mould 

 be found well covered, but copper covering 

 crumble to pieces on being removed, the acid 

 was most likely too strong, and must be more 

 diluted in the next attempt. If the young 

 experimenter will attend to these details, we 

 think it is scarcely possible for him to fail at 

 last. Perseverantia omnia vincit. 



It is hardly worth while to attempt an 

 explanation of these decompositions and de- 

 positions in a philosophical manner. In truth, 

 the whole matter is very imperfectly under- 



