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In the estimation of very small q-qantities of material there is no question that colorimetric is preferable to gravimetric analysis. The colorimetric method is generally quicker and simpler to carry out-an important factor when numerous analyses are involvedand it is not subject to the manipulative errors incurred in dealing gravimetrically with minute amounts of material. The method, however, must be reliable; it must be specific, sensitive and capable of giving consistent and reproducible results. These conditions are not always fulfilled and the colorimetric method is very often neglected in favour of a relatively more dependable gravimetric method. Such is the case with the estimation of arginine and histidine for, although several colorimetric methods are available, unless certain conditions are rigidly observed and considerable experience has been gained, the methods are prone to give erroneous results and many workers prefer the more laborious gravimetric technique.With a view to rendering the colorimetric estimation of arginine and histidine thoroughly reliable under less stringent conditions, the modified procedures described in this paper are put forward. It is proposed to employ the methods in the ahalyses of solutions of the basic amino-acids obtained by electrodialysis or precipitation with phosphotungstic acid or. by a combination of both. A subsequent paper will be published in this connection. THE ESTIMATION OF ARGININEAfter experimenting with the oc-naphthol and acetylbenzoyl methods and noting the limitations of both, it was decided that the. former was more suitable for modification. Arginine in alkaline solution gives a red colour with oc-naphthol and an oxidizing agent such as hypochlorite [Sakaguchi, 1925]. The method as generally carried out [Weber, 1930] is, however, unsatisfactory and subject to considerable errors. The reaction is complicated by the rapid destruction of colour by excess hypobromite, which is employed since it gives a more specific reaction than hypochlorite, and the usual procedure is to add urea almost immediately in order to, take up the e2tcess hypobromite. This expedient is only partially effective for, although formation of the coloured compound is instantaneous, destruction by hypobromite also begins immediately, and in the several seconds which must elapse during mixing of arginine and reagent and dispersal of urea throughout the solution, considerable loss of colour will have occurred, and full colour development will not be achieved. Unless the interval before addition of urea, the proportions of hypobromite and urea and the efficiency of mixing are always identical, it is impossible to obtain consistent results. Experimentally it is found that there is a certain optimum quantity of hypobromite with respect to the arginine which will give a maximum colour development. Slight deviations from this optimum will yield much lower results. Obviously then, although the time factor may be fairly accurately controlled, it is impossible to assess the optimum amount of ...

Many methods for chromatographic separation of amino acids are now available, but their subsequent determination, generally employing ninhydrin, often leaves much to be desired. It was felt, therefore, that there was a need for a simple method of