Meanwhile, further discoveries of the curious properties of matter were being made. For example, it had been noticed that at least three distinct varieties of sulphur existed: (1) A pale yellow, brittle solid; (2) translucent needles; and (3) soft and rubber-like sulphur. These were all different physical varieties of one and the same substance--nevertheless they are all sulphur! This element, then, can assume more than one form, and because of this, the term “allotropic” has been applied, to signify the varieties of appearance which the same substance can be made to assume. A good example of this afforded by charcoal, graphite (or black-lead) and diamond,--which would hardly be suspected of being all the same substance; and yet they are! ANALYSIS AND SYNTHESIS Compounds may be broken up into their constituents, during the process of analysis, or they may be made to combine one with another, in synthesis. All the resources of modern science have been brought to bear, in efforts to effect these various alterations or changes. Great heat, extreme cold, chemical reägents, enormous pressures, high vacua, electrical currents and sparks, bombardment with radio-activity, etc.--all have been employed in these chemical investigations. Suitable laboratories have been constructed, encasing immense boilers, huge refrigeration machines, electrical contrivances of all kinds, etc. What tremendous strides have been made in this field during the past century--from the simple glass retorts, flasks and apparatus of a century ago! But this only shows us how tremendous would be our progress could men but learn to work together, in harmony, welded together by a common interest,--instead of butchering one another, or wasting their precious lives and energies in scandals and political intrigues! But let us return to earth again--to matter--the subject of chemistry! FORMULAE AND EQUATIONS We have seen that the various chemical elements combine with one another in certain proportions. In order to express these varied reactions, chemical formulæ have been devised, which can be read at a glance, showing the changes which have taken place in any given combination. When one atom of one element combines with one atom of another, the letters signifying these elements are simply written side by side, thus: HCl. When, however, two atoms of one element combine with one of another, a small figure is placed under and to the right of the element, thus: H₂O. Here we see at a glance that two atoms of hydrogen have combined with one of oxygen, forming water. This is the simplest type of formula, and is often known as the _empirical_ formula. There is, however, another way of writing a formula, which is more expressive, thus: B A=C= B