TO PHYSIOLOGY AND PATHOLOGY. 19 



a glass rod instantly causes a deposit of crystals of bitartrate of potash. The ful- 

 minates of silver and mercury explode with the greatest violence on the applica- 

 tion of a blow, or of friction ; the same is the case with Berthollet's fulminate of 

 silver, with picrate of lead, and many other compounds. It is clear that in these 

 cases the blow or friction, or more correctly, the motion, is imparted to the atoms 

 of these combinations ; that the direction of their attraction is thereby changed, 

 and that, consequently, new products are formed. Fulminate of silver contains 

 cyanic acid. By the blow or friction, a new mode of arrangement is brought 

 about : a part of the carbon developes itself, and combines with the oxygen, form- 

 ing carbonic acid ; nitrogen developes itself with the carbonic acid, and explosion 

 is the result of the sudden transition to the gaseous form. The colorless fluid sty- 

 role becomes solid and hard through the influence of a purely mechanical motion. 

 (Sullivan.) 



HEAT SIMILAR TO THE ACTION OF A MECHANICAL FORCE. 



A number of bodies are decomposed by heat, and in these cases its action is 

 perfectly similar to that of a mechanical force. Heat acts like a wedge driven in 

 between the atoms. If between two atoms the resistance, which the chemical 

 force that held them together, has opposed to the entrance of the wedge be less 

 than the force which separated them, the atoms fall asunder, and decomposition is 

 the result. Oxide of mercury is resolved into oxygen and the metal. Heat acts 

 in the same manner on bodies composed of more than two elements. At a certain 

 temperature the fulminates of silver and mercury, Berthollet's. fulminate, and 

 picrate of lead explode. Heat alters the original mode of arrangement of the 

 atoms, and, consequently, the equilibrium of their mutual attraction ; under its 

 action they are then deposited in the directions to which their attraction is the 

 strongest. The formation of new products rests upon the establishment of a new 

 state of equilibrium, and they suffer no further change as long as they continue 

 exposed to the same degree of heat ; but if the temperature be raised, a new 

 disturbance occurs, and, consequently, a new state of equilibrium, and a new mode 

 of arrangement of the elements. On being exposed to a faint red heat, acetic 

 acid is decomposed into carbonic acid and acetone ; the carbonic acid contains 

 two-thirds of the oxygen, while the acetone contains all the hydrogen of the acetic 

 acid ; at a higher temperature the acetone is decomposed into a compound of 

 carbon which contains oxygen, and into an oleaginous hydro-carburet. Exposed 

 to a temperature of 392 F., the styrole becomes solid and hard, loses its fluid 

 character, and passes into a form resembling the most beautiful crystal glass. 



INFLUENCE OF THE CONDITION OF CHEMICAL ACTIVITY. 



It has been observed that platinum does not decompose nitric acid, and that it is 

 neither oxidized or dissolved by this acid. A compound of platinum and silver 

 dissolves, however, easily in nitric acid. 



INFLUENCE OF THE CONDITION OF CHEMICAL ACTIVITY UPON THE 

 CAPACITY OF BODIES TO ENTER INTO COMBINATIONS. 



Metallic copper does not decompose water, when boiled with sulphuric acid ; 

 certain compounds of zinc, copper, and nickel dissolve, however, easily in sul- 

 phuric acid, with a development of hydrogen. In certain relations, compounds 

 of these three metals will not dissolve in sulphuric acid, but if a trace of nirnc 

 acid be present, oxidation begins, which is then continued without further co-ope- 



