The Rev. E. Craig's Remarks on Microscopic Chemistry. 1 S 



phate of iron, the process of crystallization is very distinctly 

 observed. Sulphate of potash in solution is at first formed, in 

 which the small particles of the deep Prussian blue float. 

 The course of these coloured particles floating in the colour- 

 less fluid exhibits the currents that run in it, and soon the 

 crystallization of the sulphate of potash commences in a va- 

 riety of characteristic forms, the particles of the pigment indi- 

 cating the flowing of the tide in which they float, as the solu- 

 tion gradually forms itself into masses of crystallization along 

 the line. 



One of the most remarkable changes in the character of 

 crystallization is seen if sulphuric acid be added to carbonate 

 of copper : crystals speedily appear in the form of six-sided 

 tabular prisms. Add a little ammonia; the form of crystaUiza- 

 tion is changed entirely to long rectangular prisms with the 

 angles replaced. Add a little more ammonia and the form 

 changes to several varieties of the rhombic octohedron : a little 

 nitric acid restores again the form of the rectangular prism. 

 And in all these successive changes it is not that a few crystals 

 of another form have been superadded, but each time the me- 

 tamorphosis is seen to take place in the whole mass. 



The microscopic history of iodine in the exhibition to it of 

 a variety of agents is most interesting. Its effect as a colour- 

 ing matter on the oval molecules of starch is very pretty. It 

 is equally curious to see the application of a portion of nitric 

 acid swell those coloured globules from their centre till they 

 are torn by the internal force and dissipated. If solution of 

 iodine be added to sulphate of soda in solution, the result is 

 very beautiful. The alcohol takes up a portion of the water 

 from the sulphate of soda, which consequently crystallizes in 

 long prisms. The iodine deprived of the alcohol appears in 

 cherry-red drops, and in daik rhombic metallic-looking cry- 

 stals. 



It would be easy to multiply instances, but these must suf- 

 fice as a specimen of the interesting objects that await expex'i- 

 ment as the reward of the observer. The range of experi- 

 ments may easily be extended to those processes which require 

 heat : longer glasses must then be used which reach beyond 

 the edge of the port-object, and a small spirit-lamp applied 

 under the projecting portion of the glass will give any degree 

 of heat required either for evaporation or boiling. 



Some curious results also have been observed on the appli- 

 cation of the galvanic pile to chemical substances under the 

 microscope. For this purpose it is desirable to use a lens of 

 somewhat smaller power. The observation cannot well be 

 carried on except on a single plate of glass ; and the lens used, 



