288 MOULDING AND CASTING. 



plaster of Paris, mixed with talc, must be tempered 

 to the proper consistence with water, and the 

 sides of the box oiled. Also a straight piece of 

 stick must be put to the principal part of the 

 body, and pieces of wire to the extremities of the 

 other parts, in order that they may form, when 

 drawn out after the matter of the mould is set 

 and firm, proper channels for pouring in the metal, 

 and vents for the air ; which otherwise, by the 

 rarefaction it would undergo from the heat of the 

 metals, would blow it out, or burst the mould. 

 In a short time the plaster will set, and become 

 hard ; when the stick and wires may be drawn 

 out, and the frame or coffin in which the mould 

 was cast taken away ; and the mould must then be 

 put, first, into a moderate heat, and, afterwards, 

 when it is as dry as can be rendered by that de- 

 gree, removed into a greater, which may be gra- 

 dually increased, till the whole be red hot. The 

 animal or vegetable inclosed in the mould will 

 then be burnt to a coal ; and may be totally cal- 

 cined to ashes, by blowing for some time into the 

 charcoal and passages made for pouring in the 

 metal, and giving vent to the air, which will at 

 the same time that it destroys the remainder of 

 the animal or vegetable matter, blow out the ashes. 

 The mould must then be suffered to cool gently, 

 and will be perfect ; the destruction of the sub- 

 stance included in it having produced a corre- 

 sponding hollow ; but it may nevertheless be pro- 

 per to shake the mould, and turn it upside down, 

 as also to blow with the bellows into each of the 

 air-vents, in order to free it wholly from any 

 remainder of the ashes ; or, where there may be 

 an opportunity of filling the hollow with quick- 

 silver, it will be found a very effectual method of 



