On the estimation of uric acid in urine

I N a paper read before the Royal Society last year,' I described a method for the estimation of uric acid in urine, by means of saturation with ammonium chloride.Since the reading of that paper I have made considerable use of the method, under the most varying conditions ; and it is the purpose of the present paper to give the results of this extended experience, and to describe fully the details of the process in a perfected form.After using it continuously for more than a year, with a large number of normal and pathological urines, I am strengthened in my belief that it is a process of very great accuracy.By its means uric acid may be estimated with an error of less than 1 per cent.; a degree of accuracy unattainable in the case of any of the other organic constituents of the urine. I. THE SEPARATION.The convenience of separating the ac.id as an ammonium salt is very great, as compared with that of its precipitation as the compound of a heavy metal, such as silver.The danger of reduction, which is SO great in the latter case, is obviated ; while the ammonium salt is easy to filter, and permits of the liberation of the free acid with great readiness.These are merits which belonged to the well-known Fokker Salkowski process, and if in the latter the uric acid underwent even approximately complete precipitation, there would have been little need to have sought further for a method of determining this important urinary constituent.Unfortunately the results obtained by the Fokker-Salkowski process require a very large correction for incomplete precipitation.In its most approved form, one is directed to add 30 milligrammes to the result obtained when working on 200 C.C. of urine.2Now, as the product actually weighed in such a case will average some 100 milligrammes, it will be seen that the correction factor is most undesirably large.If it were really a constant, this would not, of