10 SCIENTIFIC AMUSEMENTS. 



if moved too soon the impression will be damaged and the mould 

 mis-shaped. Another way of operating is to form the plastic gutta- 

 percha into a ball and lay it on a plate, flattening it down to a 

 disc ; the coin is then placed on this and well pressed into it, and 

 finally covered with a flat board and weight as before. 



When the gutta-percha mould thus obtained is filled with plaster 

 of Paris slip and the latter allowed to harden, on removal of the 

 plaster cast an exact facsimile of one side of the coin used is 

 obtained. The plaster cast should be trimmed at the edges and 

 dried, and then rubbed with bronze powder of coppery, silvery, or 

 golden hue, according to the metal of which the coin is made. A 

 second cast being made of the other side of the coin and similarly 

 treated, the two casts enable both sides of the coin to be viewed 

 together without having to remove the coin and turn it over. If 

 antique coins, seals, &c., can be borrowed from friends for the 

 purpose of thus copying, with a little trouble an interesting 

 collection of seals and impressions may soon be accumulated. 



Expt. 7. To make Casts in Fusible Metal. Eose's " fusible 

 metal " is a mixture of three different kinds of metal, as follows : 



Bismuth, 8 parts. 



Lead, . . . . . . 4 to 5 ,, 



Tin, 2 to 3 ,, 



To prepare it obtain quantities of these three metals in about 

 these proportions. First melt the lead in a small crucible, then 

 add the bismuth, and finally the tin, and stir well together with 

 a piece of tobacco-pipe stem, or a thick knitting-needle. This 

 mixture of metals possesses the remarkable property of melting 

 much more easily than any of the three constituents from which 

 it is prepared, whence its name. If made in exactly the right 

 proportions, it will melt in boiling water. The melted metal may 

 be placed in the lid of a pill-box, and the object to be copied 

 pressed on to it as in taking a gutta-percha or plaster cast ; metal 

 objects, such as coins and medals, should be previously well greased 

 or blackleaded to prevent any chance of the fusible metal sticking 

 permanently to them. Or the melted metal may be poured into a 

 plaster mould, so that when set hard it will form a replica of the 

 object from which the mould was taken. Owing to the low 

 temperature at which fusible metal melts, it is possible to use 

 it for obtaining impressions of fine lace, skeleton leaves, and 

 such like delicate objects without burning them. By depositing 

 copper by means of electricity on the moulds thus formed, 

 beautiful metal copies of the patterns thus impressed in the 

 fusible metal may be obtained ; or plaster casts may be struck 

 from the metal moulds thus produced. 



