260 BENJ. TIKE'S, JR., DESCRIPTIVE CATALOGUE. 



combine solution of iodine with solution of sulphate of soda. 

 The alcohol in the solution of iodine takes part of the 

 water from the soda, and the rest of the sulphate of soda 

 immediately crystallizes in prisms. The iodine, deprived of 

 the alcohol, is developed in cherry red drops of liquid and 

 in dark rhombic crystalls. In fact, in the endless variety 

 of objects that can thus be brought before the eye, both 

 the young student and the scientific chemist will find at once 

 a means of amusement and of deep analytic investigation of 

 the most fascinating and important kind. Evaporation or 

 boiling may be carried on in the same way by extending 

 one end of the glass over the port-object, and placing under- 

 neath it a small spirit-lamp, so that even the changes inci- 

 dent to this state may also be examined. The observations 

 made by examining the effect of chemical agents on the 

 juices of plants, offer a subject of very great interest and 

 importance. 



But the examination of chemical action may be carried 

 still further by the application of the galvanic battery under 

 the microscope. A small battery of thirty plates, two inches 

 square, is sufficient for the purpose. Place any chemical 

 agent, as liquor potassse, on one glass plate ; use alow power 

 in the microscope to prevent vapor gathering on the lens, 

 owing to its nearness ; and then guide the two wires near 

 to each other in the drop of liquid. The oxygen will go to 

 one pole, and the potassium to the other. The dendritic 

 foliations that form at one pole and grow out towards the 

 other, in ammonia and nitrate of silver and other agents, 

 are very beautiful. The effect visible in albumen, the white 

 of egg, is very interesting. It has long been observed that 

 albumen coagulated on the application of galvanic power ; 

 the microscope shows quite distinctly what this coagulation 

 is. Albumen is a vesicular structure. The action of gal- 

 vanism is to burst these vesicles, and draw out the liquid 

 contained in them to one pole, while the vesicles all shrink 

 up towards the other ; and their approximation gives the 

 character of whiteness and solidity that appears. The 

 arrangement of these vesicles, and the nerves or bands along 

 which the cellules are arranged, are easily distinguished be- 

 yond the possibility of mistake. 



To these observations may be added, the examination of 

 various crystallizations in polarized light. Between the 

 reflecting mirror and the port-object insert a plate of tour- 



