26 SCIENTIFIC AMUSEMENTS. 



certain fluids, such, as carlon disulphide, and allowing them to 

 evaporate. This kind of action will be described later on (Chapter 

 V.). Many solid substances can be thus crystallised by dissolving 

 them in an appropriate solvent liquid and removing this by 

 evaporation, or by making a hot solution and allowing it to cool ; 

 such operations are extremely common in chemical manufactures 

 as well as in laboratory experiments. 



Expt. 20. To make Teaspoons that Melt when used. The 

 alloy above described (Expt. 7) under the name of " Rose's fusible 

 metal " will, as already stated, melt in boiling water, so that if a 

 hollow plaster mould of a teaspoon be made and fusible metal 

 cast therein, a teaspoon will be obtained which will melt if very 

 hot water be poured into it, or if boiling water be stirred with 

 it. If the water be not quite boiling, however, as is pretty sure 

 to be the case when tea from a teapot is used, in all probability 

 the heat will not be quite sufficient to melt the spoon. By 

 melting the alloy and adding to it a small quantity of quick- 

 silver, it is possible to make a mixture which, though solid at the 

 ordinary temperature, will melt in water very much below the 

 boiling-point. Another variety of easily-fusible alloy, known as 

 " Wood's alloy," is made by melting together 



Bismuth, . . . . . 7 to 8 parts. 



Lead, 4 



Tin, 2 



Cadmium, 1 to 2 ,, 



This mixture melts at about 70 centigrade and Rose's at 

 about 98, the temperature of boiling water being 100 and that 

 of melting ice zero ; on this scale an ordinary warm room has a tem- 

 perature of from 15 to 20 C., whilst the temperature of the blood 

 is about 37. Another kind of scale for measuring temperatures, 

 called Fahrenheit, is sometimes used, and on this scale water boils 

 at 212 and freezes at 32 (vide Expt. 28). 



It appears to be a pretty general rule that when two different 

 kinds of solids are mixed together the mixture melts more easily 

 than would be expected from the temperatures at which each of 

 the solids melts separately ; more especially is this the case with 

 mixtures of metals. Thus ordinary plumber's solder is made of 

 lead and tin mixed in proportions differing somewhat according to 

 the purpose for which the solder is wanted, the coarser kinds 

 containing more lead and the finer kinds more tin; several of 

 these mixtures melt at temperatures not high enough to cause 

 either tin or lead alone to fuse, and it is this property chiefly 

 which enables the mixture to be used as a solder to cement together 

 gas and water pipes and for such like purposes. 



