12 The Rev. E. Craig's Remarks on Microscopic Chemistry. 



down, as it will disturb the action. It should therefore be 

 somewhat smaller in dimension then the lower glass, to di- 

 minish the risk of its being moved accidentally. The pres- 

 sure of the one glass upon the other spreads the whole com- 

 pound into one nearly uniform film upon one level, and con- 

 sequently the whole action going on may be examined by 

 gently moving the glass in different directions. 



The few experiments which I describe are those of com- 

 binations and decompositions with respect to which the results 

 are universally known. They are detailed, therefore, only 

 to exemplify the very great facility with which the most mi- 

 nute phasnomena attending chemical action can be seen by 

 means of the apparatus described, and which are lost sight of 

 in operating with larger quantities, in the retort or the test- 

 tube 



For instance : put on the lower glass a very small portion 

 of carbonate of copper, and on the upper glass a drop of ni- 

 tric acid, and bring them together. The carbonic acid is 

 seen to evolve in beautiful globules with more or less violence, 

 which gradually merge into each other: the round particles of 

 the carbonate gradually disappear as the solution of the ni- 

 trate of copper is formed. A iew massy crystals of a deep blue 

 colour appear amongst the remains of the carbonate, whilst in 

 the clear solution multitudes of small rhombic tabular crystals 

 are deposited in all their possible varieties of proportion. 

 Raise the upper glass gently and add a drop of ammonia ; 

 the crystals of the nitrate instantly dissolve and disappear. 

 The nitrate of ammonia is spread over the glass in a great 

 variety of forms, and this is interspersed with groups of prisms 

 of the deep violet- coloured ammoniiiret of copper. 



The phsenomena attendant on the productionof the chloro- 

 chromic acid are ecjually beautiful. The action of the sulphuric 

 acid on the chloride of sodium for the elimination of the mu- 

 riatic acid is at first very violent. The whole field becomes 

 turbid with green and red particles rushing onward in different 

 currents. At length it begins to clear. Often from one brighter 

 spot a series of globules begin to arise, increase, and rush for- 

 ward in one continued course, attended on each side by a mul- 

 titude of small drops of the chloro-chromic acid; and finally, 

 as the action subsides, a field of clear amber-coloured liquid 

 appears filled with varied crystals of sulphate of soda and sul- 

 phate of potash, sprinkled irregularly with the blood-red 

 drops of the acid, and occasionally mixed with cubes of the 

 chloride of sodium and cubes of the bichromate of potash that 

 yet remain undecomposed. 



On bringing together the ferrocyanate of potash and sul- 



