What, however, constituted the greatest contribution of Mrs. Richards to the public health was the part she took in the great sanitary survey of the waters of the State of Massachusetts. During this long and laborious investigation she analyzed more than forty thousand samples of water. These analyses exhibited the condition of the water from all parts of the state during all seasons of the year and were of the greatest value in solving a number of important problems in state sanitation. But notwithstanding the drafts made on her time and energy by her classwork in the laboratory and her occupation as sanitary engineer for scores of public and private institutions, she still found leisure to engage in many important movements which had in view the public health and the betterment of sanitary conditions in city and country. It is safe to say that no one ever put her knowledge of chemical science to more practical use or made it more perfectly subserve the public weal than did Mrs. Richards. To spread among the masses a knowledge of the principles of sanitation, to make them realize how indispensable to health are pure food, pure water, pure air and life-giving sunshine was her great mission in life, and in this she displayed an energy and a tireless zeal which were an inspiration to all with whom she came into contact. This indefatigable woman, it is proper to record here, might have distinguished herself as a discoverer in chemical science had she elected to devote her life to original research rather than to utilizing the knowledge already available for the welfare of her fellows. Thus, after a careful analysis of the rare mineral samarskite, she found an insoluble residue which led her to believe might contain unknown elements. This view she repeatedly expressed to her co-workers in the laboratory. But she was unwilling to take from what she regarded more important work the time necessary for making investigations which might have given her undying fame as a discoverer. For not long afterward this insoluble residue, in the hands of two French chemists, yielded the exceedingly rare elements, samarium and gadolinium. Another chemist of a less altruistic nature than Mrs. Richards would not have resisted the temptation to achieve distinction in the domain of original research. But where there was so much suffering to be relieved and so much ignorance to be removed regarding the most fundamental principles of sanitation, this philanthropic woman preferred to put to practical use what she called "the considerable body of useful knowledge now lying on our shelves."