PROCEEDINGS OF THE POLYTECHNIC ASSOCIATION. 427 



Iodine melts at 107°C. and changes into a splendid blue vapor 

 atl75<^C. 



Sulphur melts at 115° C, and becomes a deep yellow vapor at 

 440° C. Sulphur has several modifications of form, or different 

 allotropic states, in which it is differently affected by heat. 



Selenium melts at a little over 100° C. In the crystalline form 

 it softens at 217° C, and does not become completely fluid until 

 above 250° C. Heated in a close vessel it boils at a little above 

 a red heat. 



Tellurium, which has the appearance of a metal, fuses a little 

 below 480° C, and at a high temperature becomes a vapor. 



Arsenic is not known in a liquid state. At 180° C. it begins to 

 volatilize, without fusing. This peculiarity is represented by a 

 thick line extending from the centre to the point where it is shown, 

 as a vapor. This element, as well as tellurium, I prefer to class 

 among the metals. 



Phosphorus melts at 45°, and boils at about 229° C. 



The metals are solid at ordinary temperatures, with the excep- 

 tion of Mercury, a fluid which freezes at 39° C, and becomes a 

 colorless vapor at about 360° C. A large majority of the metals 

 melt at a high temperature; yet several of the light metals of the 

 alkaline class become fluids below the boiling point of water. 



The fifty-one metals, including arsenic and tellurium., are repre- 

 sented by the radial lines in figure 4; the shaded line projecting 

 directly downward denotes the fluid, mercury. This diagram in- 

 cludes all the Jcnovm elements, arranged so as to show with clear- 

 ness their classification as fifty-one metals, and thirteen non-metallic 

 bodies; also their actual state at ordinary temperatures, embracing 



Gases _ 5 



Liquids 2 



Solids 57 



Total 64 



The density of the gaseous elements is represented by fig. 5.. 

 Hydrogen the lightest, being at the top ; fluorine and chlorine, 

 the heaviest two at the bottom ; oxygen and nitrogen having an 

 intermediate position on the sides. The equal parallelograms pro- 

 jecting from the sides, represent equal measures or volumes of gas 

 at the same temperature and pressure, and the wide mark or bar 

 within each parallelogram shows their relative density or specific 

 gravity. Assuming that one volume of hydrogen weighs 1, one 



