1823.] Mathematical Principles of Chemical Philosophy. 249 



them ; if the glass be unannealed, i. e. allowed to cool rapidly, 

 it hardens rapidly, and the particles cannot return to that 

 position in which they would be placed were the cooling very 

 gradual : hence, from a former paper, the particles may have 

 the same position when cold which they had in a fluid state ; 

 but if the place of one particle be disturbed, the equilibrium of 

 the whole system will be destroyed, and the mass, however 

 large, will be broken to pieces, by the action of a small piece of 

 any hard matter : hence the peculiar properties of bottles of 

 unannealed glass, Prince Rupert's drops, &c. Also, owing to 

 the great tenacity of glass at the annealing temperature, by that 

 process, the particles can never assume that position in which 

 their attracting forces tend to place them ; hence then they will 

 always have a tendency to change, when the situation of a part 

 is altered ; the cutting diamond may depend upon this prin- 

 ciple. 



The mechanical properties of liquids prove that the repulsive 

 force of heat decreases more rapidly than the centripetal force. 

 The parts of a liquid have perfect freedom of motion, therefore 

 the particles cannot touch each other ; since they are at a cer- 

 tain distance from each other, which is permanent, the tempera- 

 ture being constant, they must be in equilibrio between two 

 opposite forces, which are equal at that distance. If the foi - ce 

 of repulsion vary less rapidly than the other, there may be a 

 distance at which the two forces are equal ; but if two particles, 

 under such circumstances be disturbed, the equilibrium is. 

 destroyed, and, if brought nearer, they will come into contact ; 

 if removed to a greater distance, they will separate indefinitely, 

 which is contrary to the fact : if the force of repulsion vary 

 most rapidly, both forces, Prop. I. will tend to that point, so 

 that the particles can be only at that distance from each other. 

 Again : if the repulsive force vary less rapidly than the other, 

 increase of heat would cause contraction, and vice versa, which 

 is absurd. 



Cor. 2, Prop. VII. shows why dry unbaked clay, white lead,, 

 prussian blue, and many other solids, insoluble in water, are 

 reduced to a paste when immersed in it ; these substances are 

 well known to be sensibly porous, and it is evident that the force 

 with which the water tends to enter into and expand the pores, 

 exceeds the cohesive force of those solids. 



The tenacity of moist clay results from a similar cause. Clay 

 also will contract permanently by the application of heat. By 

 the first application of heat, the water contained in the clay will 

 be expelled : it is then filled with minute pores ; if the tempera- 

 ture be increased, the force of cohesion is considerably dimi- 

 nished, and the sides of the pores will have a tendency to 

 approach each other ; consequently the volume will contract, 

 and the contraction will be permanent. 



