6 SCIENTIFIC AMUSEMENTS. 



venient ; with small ones, unless they are required to be heated 

 extremely hot, a fire is not necessary, as a " Bunsen gas-lamp " 

 (fig. 4) will furnish enough heat for most purposes when placed 

 so that the flame laps round the crucible supported by a triangle 

 of wire (fig. 5), on the ring of a retort stand (fig. 6), or tripod 

 (fig. 7). When gas is not available, a spirit-lamp (fig. 8) may 

 often be employed instead; the cap serves to prevent loss of 

 spirit by evaporation when the lamp is not in use, whilst the 

 stoppered orifice permits of the introduction of fresh spirit as 

 required. 



Expt. 2. To take Impressions in Sealing- Wax. Some kinds 

 of solids possess the property of becoming plastic when warmed or 

 heated, although when allowed to cool again they become hard as 

 at first ; sealing-wax affords a good example of this. To take a 

 good clear impression of a well-cut seal or of a coin, &c., appears 

 to be a tolerably simple operation, but is really one requiring some 

 considerable amount of care in execution ; the wax should be as 

 little as possible smoked by the flame in melting, and the whole 

 mass of melted and softened wax on the paper, &c., intended to 

 support the impression should be stirred together by a sort of 

 circular motion of the rod of wax, so that all parts of it may be 

 about equally hot and therefore equally soft ; if this is not attended 

 to, a bad impression will probably result, parts of the wax being 

 too cool and partially hardened again to " give " sufficiently when 

 the seal is applied. On the other hand, if the sealing-wax is too 

 hot and fluid, and especially if the seal is hot also, the wax may 

 stick to the seal so firmly as to render it difficult to remove it 

 after complete cooling without breaking the wax ; whilst in 

 taking a cast of a large piece of metal (such as a good-sized medal) 

 the chilling action of the metal is apt to harden the wax so 

 quickly that it has not time to penetrate into all the crevices and 

 interstices of the device, and so a blurred and imperfect impression 

 results. 



Expt. 3. To make Plaster Casts. Certain solids, when 

 powdered and stirred up with a little water, possess the power of 

 forming a semi-liquid mass which shortly " sets " hard, somewhat 

 as a jelly solidifies on cooling. Plaster of Paris and various kinds 

 of cement owe their usefulness to this property. To take an 

 impression of a flat object, such as a coin in plaster of Paris, the 

 simplest method of proceeding is to get the lid of a pill-box a little 

 larger than the coin, and lay it flat on a table, saucer-fashion. A 

 little good plaster is now mixed with water to a thick cream in a 

 cup by means of a spoon, and the box-lid filled by pouring the 

 " slip " into it. The coin is previously prepared by being very 



