Chemical analysis is founded upon the fact that when certain chemicals are mixed together they will, or they may, unite to form quite a different chemical. This newly formed chemical is probably a different colour to the substances which were used in its making, or again the original chemicals may be soluble in water and the new chemical insoluble, in which case it will form a cloudiness known as a precipitate. An example may help to make our description clearer. Suppose we take some common table salt and dissolve it in a little water in a glass, then add to this a little solution of nitrate of silver, which is sold under the name of lunar caustic, we shall find that a white cloudiness is formed when the liquids mix, although originally they were both clear. The reason of this cloudiness is that the two substances, dissolved in water have united with one another to form a third substance which will not dissolve, therefore it settles down as a fine powder. Long experience has taught analytical chemists exactly what chemicals to add to test for all the common substances, by the formation of these precipitates; so that, if any powder were given to one of these scientists he could tell its composition by applying certain tests. In this chemical analysis considerable quantities are required and it is often necessary to test very small samples, so small that the ordinary methods are out of the question. This is where the microscope scores, because with this wonderful instrument, only drops are required and tests of corresponding delicacy may be made; in fact, by modern microscopic methods it is possible to detect the presence of as little as ten thousandth part of a grain of arsenic, or quicksilver or of the deadly poisons, Strychnine or Prussic Acid. In testing for poisons the microscope is invaluable. Frequently only the most minute traces of the poison occur in the system and the modern microscopist who makes a study of poisons and their detection can solve mysteries which would have baffled all the scientists in the world in days gone by. Our chemical studies with the microscope may well begin with various common crystals; they are usually easy to prepare; the process of crystallization is always interesting to watch, and as objects for the microscope it would be difficult to find anything more beautiful than these home-made gems. All crystals should be examined by reflected as well as by transmitted light. When we are working with the former lighting, a piece of black paper beneath the slide will help to show up the objects to better advantage.