The apparatus here described was designed in the first instance to provide a means for the rapid preparation and accurate adjustment of the liquid mixtures now commonly used for mineral determinatiom For this purpose refractometers of the Pulfrich type are inconvenient, not only on account of the risk of error due to the complicated centring of the prism or hemisphere and scales, but also because the transfer of a drop of liquid to the refracting surface renders the determination especially liable to errors arising from temperatm'e variation, from contamination of the drop, and from evaporation. Ful%her, in the preparation of liquid mixtures the frequent transference of small quantities to a refractometer is the source of much inconvenience.