226 Objects for the Microscope. 



will show the formation of crystals in primitive cubes, ter- 

 minated by quadrangular pyramids. The water slowly 

 evaporates, and the atoms held in solution return to their 

 natural form. 



ACETATE OF COPPER 



is made by dissolving common verdigris in excess of diluted 

 acetic acid, and when crystallized on the slide will exhibit 

 the phenomena of dichromism or double colour, deep blue 

 and yellowish green. 



SULPHATE OF COPPER. 



Blue vitriol dissolved in water, and likewise treated with 

 a gentle heat, will show the formation of beautiful blue 

 crystals in oblique rhomboidal prisms. 



ALUM 



does not polarize, but gives crystals of the octohedral form. 



OXALURATE OF AMMONIA. 



This is most beautiful in the formation of its crystals ; 

 they appear on the slide as circular discs-or very flat spheres, 

 consisting of minute needles radiating from the centre, and 

 sometimes projecting beyond the circumference of the disc. 

 Without the selenite stage these discs are like brilliant 

 little white stars, traversed by a black cross ; with the 

 selenite they are splendid objects, the colours often disposed 

 in concentric rings. 



MUREXIDE OR PURPURATE OF AMMONIA 



is an artificial product of the decomposition of uric acid. 

 The crystals are flattened, short, four-sided prisms, of bright 

 ruby red by transmitted common light, and the two broad 

 surfaces are emerald green by reflected light. 



HYDROCHLORATE OR MURIATE OF AMMONIA. 



This salt crystallizes in cubes, octohedra, and trapezohedra. 

 A very little of the powdered salt dissolved upon a slide 

 and heated gives a beautiful exhibition of feathery crystals 

 darting across the field of sight, and breaking into stars 

 and crosses. They do not polarize. 



