-1859] WRITINGS OF JOSEPH HENRY. 115 



a similar character has been observed with reference to bodies 

 belonging to the class which the chemist calls simple or 

 elementary, because they have not as yet been decomposed. 

 Of these bodies we may mention ox3^gen, chlorine, sulphur, 

 and phosphorus. They all assume under certain conditions 

 entirely different properties to such an extent as almost to 

 lose their identity. Oxygen, when exposed to a series of 

 sparks of electricity, is converted into a substance called 

 ozone, of which we shall speak more fully hereafter. Sul- 

 phur, exposed to a temperature of 226° F., is melted, and if 

 maintained in fusion at a temperature not exceeding 300°, 

 and then suddenly thrown into water, will be found to have 

 suffered no change; if however the fusion be continued 

 above 300°, the material becomes black and almost solid, 

 and if it now be poured into water it maintains its dark 

 color, and assumes a consistence of heated glue or softened 

 India rubber. In this condition its medical and other prop- 

 erties are changed. Sulphur is also capable of assuming two 

 different cr3'Stalline forms belonging to two primitive classes 

 entirely distinct. Phosphorus undergoes a similar change, 

 and chlorine, after exposure to the light, exhibits new prop- 

 erties. Phenomena of this kind are classed under the head 

 of alloiropism (literally, of another turn or fashion). 



Organic Molecules. 



The groups of atoms which we have thus far been con- 

 sidering are principally those which have been formed 

 under the influence of what is called the chemical force, and 

 result from the ordinary attraction of the atoms. These are 

 comparatively simple groups; but there is another class of 

 groups of atoms of a much more complex character, which 

 are formed of new combinations of the ordinary atoms 

 under the influence, or (we ma}' say) direction of that myste- 

 rious principle called the vital force. We are able to con- 

 struct a crystal of alum from its elements by combining sul- 

 phur, oxygen, hydrogen, potassium, and aluminum; but 

 the chemist has not yet been found who can make an atom 

 of sugar from the elements of which it is composed. He can 



