CHANGE IN CONDITION OF COHESION. 43 



we deal with in building up the structures on 

 the earth are of strength we use iron, stone, 

 and other things of great strength ; and only 

 think that all those structures you have about 

 you think of the Great Eastern if you please, 

 which is of such size and power as to be almost 

 more than man can manage are the result of 

 this power of cohesion and attraction. 



I have here a body in which I believe you 

 will see a change taking place in its condition 

 of cohesion at the moment it is made. It is at 

 first yellow, it then becomes a fine crimson red. 

 Just watch when I pour these two liquids 

 together both colourless as water. [The 

 Lecturer here mixed together solutions of per- 

 chloride of mercury and iodide of potassium, 

 whenayellow precipitate of biniodide of mercury 

 fell down, which almost immediately became 

 crimson red.] Now, there is a substance which 

 is very beautiful, but see how it is changing 

 colour. It was reddish-yellow at first, but it 

 has now become red. ( 8 ) I have previously pre- 

 pared a little of this red substance, which you 

 see formed in the liquid, and have put some of it 

 upon paper. [Exhibiting several sheets of paper 

 coated with scarlet biniodide of mercury. ( 9 )] 



