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the chair of Physics at that time. As his duties in Trinity required him to teach mineralogy, he formed a collection of minerals, numbering about three thousand specimens, gathered largely by his individual exertions in the field.

As a teacher he strove to impart knowledge in an attractive way, believing that, by combining entertaining diversions with serious instruction, students would both comprehend and retain facts better than if presented in a dry, formal manner. Whenever it was possible he availed himself of object teaching; although he allowed in the class-room temporary displays of humor, his pupils understood that this was to be enjoyed and not abused, and always showed their teacher sincere respect. The experience gained in teaching analytical chemistry at the School of Mines he combined with the methods in vogue when he was called to the position of assistant, and the results he published in a volume entitled Student's Guide in Quantitative Analysis (New York, 1882; third edition, 1889).

In 1885 the President of the United States appointed him an assay commissioner.

While engaged in instruction Dr. Bolton carried on a number of original researches in chemistry, of which the more important are his investigations on the salts of the rare metal uranium, the results of which he published in several papers, 1866-'70. In 1872-'73 he assisted President Henry Morton, of the Stevens Institute of Technology, in researches on the fluorescent and absorption spectra of uranium salts, preparing a large number of compounds, including several new to science; the published results are in their joint names (American Chemist, 1873).

Between 1877 and 1882 he published three memoirs on the Application of Organic Acids to the Examination of Minerals (Annals of the New York Academy of Sciences), in which he showed the power of the organic acids in decomposing minerals, as well as their utility in determining varieties based upon definite reactions. He directed attention to the advantage of dry citric acid over the liquid mineral acids in geological field-work, owing to the perfect safety of transportation of the former. These methods have been incorporated in the last edition of Elderhorst's Manual of Blowpipe Analysis. The space at our disposal precludes mention of several minor original observations.

Dr. Bolton early in his studies felt the need of those important keys to knowledge, bibliographies, and has devoted much labor to the preparation of special and general works of this nature. His first effort in this direction was an Index to the Literature of Uranium, published in the Annals of the New York Lyceum of Natural History in 1870; this reached a second edition in 1885 (Smithsonian Annual Report), and has formed the model on which