Raphael Meldola FRS (1849 - 1915) was a distinguished British chemist and entomologist. The Royal Society of Chemistry awards a Meldola Medal each year. The book is based on a course of lectures given at Finsbury Technical College."e;THE lectures forming the subject of this little volume were delivered during the spring term of last year as a special course at the Finsbury Technical College, and were addressed to a mixed audience, composed of chemical students and practical photographers. In selecting the present topic, there has been no attempt to impart instruction in the Manipulative detail of Photography, since there are already before the public a large number of excellent works dealing with this branch of the art. It is only with the chemical principles underlying the subject that these lectures attempt to deal, and it is hoped that the mode of treatment adopted may serve the purpose of convincing photographers how essential is some knowledge of Chemistry for the successful carrying on of their operations. With respect to students of technical science, it is always a most useful intellectual discipline to have presented in a systematic form the application of the general scientific principles which form the subjects of their every-day studies to some particular branch of technology. The interest evinced in the lectures, both by students and practitioners, has encouraged me to offer them in the present form, which is substantially the same as that adopted for delivery."e;-Introduction.