CHEMISTRY AND THE MICROSCOPE 



We shall find it interesting to try experiments in 

 mixing two different substances, then we shall pro- 

 bably obtain crystals totally unlike those of either 

 of the ingredients. As an example of this method, 

 let us make a saturated solution of a mixture of blue 

 vitriol and magnesium sulphate in water. Place a 

 drop of the solution on a slide, heat over a flame, 

 not only till dry, but till the substance left on the 

 slide begins to melt. We must use every care not 

 to crack the slide, and this may best be accomplished 

 by keeping it moving while over the flame. Now if 

 we watch our object through our microscope we can 

 witness the formation of wonderful feathery crystals, 

 as the slide cools. 



Some strikingly beautiful results may be obtained 

 in another manner; the method is used by analysts 

 in their so-called fusion tests. We take a small grain 

 of some substance, say, lead nitrate, place it in the 

 centre of our slide, cover with a cover slip, and warm 

 i over a flame till it melts. Then, taking a similar- 

 I sized grain of another substance, such as saltpetre, 

 we place it against the edge of the cover slip on the 

 side opposite to the lead nitrate. Further warming 

 will cause the saltpetre to melt, and run below the 

 slide and mix with the lead nitrate. If we watch 

 the meeting of the two chemicals a wonderful sight 

 will reward us. The lead compound forms a 

 " beautiful crystalline skeleton," whilst the saltpetre 

 forms six-sided stars at the opposite side of the cover 

 slip. The experiment may be repeated, using lunar 

 caustic and saltpetre, also the iodides of silver and 



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