Chemical theories are treated in a subordinate way, as it is believed that the attention should first be directed to the simpler facts of the subject and the methods by which these facts are learned. A brief Statement of a few of the prevailing hypotheses is given in Chapter XIV. Whether it will be advisable for the pupils to spend any time in studying this chapter will depend upon their age and their mental attainments. If all they can do is to learn the state ments by heart and repeat them without showing any signs of comprehension, then unquestionably the chapter should be omitted. It should be remembered that the object of the course laid down in this book is not to make chemists, but to help to develop.