CHEMICAL PARADOXES. . 343 



over which it is placed may be, it will not burn. The water Will boil, and the 

 heat be absorbed, or rendered latent, in the production of steam. An egg can 

 thus be boiled in a paper saucepan— quite in the Easter vein if we were a little 

 earlier in the season. 



A sieve may be made to hold water or to float. If the interstices are very 

 fine and the wire bright and dry, the water will not wet it, because a film of air 

 will adhere to the wires. The lower surface of the water is divided by the meshes 

 into a number of httle spheroidal projections, in which the capillary force or in- 

 ternal gravitation and also cohesion come into play. These hold the water to- 

 gether so that some considerable power is required to force the water through the 

 meshes. Thus we can put quite a quantity of water in a fine sieve, or place one 

 in water and it will float. If the wires are not perfectly bright we may distribute 

 over their surface some powder which water will not wet. The dust of bitumin- 

 ous coal is excellent. Carrying out this principle, needles, if bright may be made 

 to float without the least trouble, and will float for a long time. 



Water is to be made to boil by cold. A flask half full of water is maintained 

 at ebullition for some minutes. It is removed from the source of heat, corked, 

 inverted, and placed in one of the rings of a retort stand. If cold water is poured 

 on the upturned bottom of the flask the fluid will start into violent ebullition. 

 The upper portion of the flask is filled with steam which maintains a certain pres- 

 sure on the water. By cooling the upper portion of the flask some of this is con- 

 densed, and the pressure reduced. The temperature at which water boils varies 

 with the pressure. When it is reduced water boils at a lower heat. By pouring 

 the cold water over the flask we condense the steam so that the water is hot 

 enough to boil at the reduced pressure. To assert that water boils by the appli- 

 cation of cold is a chemical sophism. 



It seems paradoxical to see a genuine metal melt in boiling water. It is a 

 general rule that alloys melt at a lower temperature than any of their components. 

 By making an alloy of cadmium, bismuth, lead, and tin, in proper proportions, 

 we form a compound that will melt far below the boiling point of water, or about 

 160° F. Yet the melting point of tin, the most fusible of the four, is over 450° 

 F. A good way to exhibit this is to make teaspoons or punch ladles of it so that 

 they will melt in the hot fluid. It would be an illustration of the old proverb, 

 "There is many a slip 'twixt the cup and the lip." 



Double decompositions are responsible for many of our titular experiments. 

 By mixing solutions of ferric oxide and potassic ferrocyanide we oDtain Prussian 

 blue. The solutions may be so diluted as to be colorless. So two colorless solu- 

 tions produce a colored one, the suspended precipitate coloring the mixture. So 

 may chrome yellow, or lead chromate, and mercuric iodide, and hundreds of 

 other reactions be made to repeat this phenomenon. The acid radicals in these 

 cases change places with each other. By proper succession very pretty effects 

 may be produced. Thus five colorless solutions may be made to produce a color- 

 less, a red, a colorless, a white, and a black mixture, all that is necessary being 



