The chromograph, a new device for making confined spot tests: on .reagent papers, is described. The device is used to confine areas of definite size on a strip of reagent paper fed through the apparatus, and to control automatically the rate of flow of test so.lution through the confined spot. After a spot test is completed, the sample number may be wri'tten on the paper, and the paper.pulled through the apparatus to bring into position a spot oft an unused portion of the reagent paper for the next teat. The strips of paper containing the spots serve as semipermanent records of tests performed. The rate of flow of test solution through the reagent paper is controlled by the pull of a column of water and/or the filtrate from previous testa, and by a capillary tip which decreases the rate to less than that permitted by. the. reagent paper alone. Procedures for chromographic determination of nickel with djUot.etnylglyoxime reagent paper and of copper with rubeanic acid reagent paper are described. The chrfofciiDgraph has been used sucessfully in locating nickel-and copper-bearing formations by testing samples of the overlying soils ACKNOWLEDGMENTS Details of design of the chromograph were made by Joseph F. Mullins, instrument maker at the Bureau of Plant Industry, U. 3. Department of Agriculture. His help and that of Frederick CJ. Settle, who constructed the chromographs, made this study possible. Soil samples for the field trial were collected by Charles Milton and H. E. Hawkes. George E. Blandford, Jr., assisted in the analytical work during the field trial.
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