1892.] On the Estimation of Uric Acid in Urine. 93 



in their power of reducing blood-pressure, and of inducing muscular 

 contraction. 



This order appears to be the result not so much of the direct 

 physiological influence of the substituted methyl groups as of the 

 increased chemical instability which their presence confers on the 

 higher members of the series. In respect of the duration of sub- 

 normal pressure, as well as of the rapidity with which muscular con- 

 traction ensues, the activity of the nitrites is expressed by an order 

 which is for the most part the reverse of that representing their 

 power in accelerating the pulse, reducing blood-pressure, and con- 

 tracting muscular fibre, this order being in general contrary to that 

 of the homologous series. In these respects the more volatile nitrites 

 of low molecular weight which contain relatively more nitroxyl are 

 the most active. It appears probable that these simpler nitrites 

 more readily attach themselves to certain constituents of blood and 

 muscle, and thus act more quickly than the higher compounds, whilst 

 their greater stability causes their effects, i.e., reduction of blood- 

 pressure, &c., to endure for a greater length of time than that of the 

 higher and more easily decomposed bodies. 



A large proportion of an organic nitrite is changed into nitrate in 

 its passage through the organism, and is excreted as an alkali nitrate 

 in the urine. 



The results which have been gained by this research have an im- 

 portant bearing on the therapeutic employment of the nitrites. 

 It is proposed elsewhere to consider what the outcome of this 

 investigation is for practical medicine. 



V. " On the Estimation of Uric Acid in Urine : a New 

 Process by means of Saturation with Ammonium Chloride." 

 By F. GOWLAND HOPKINS, B.Sc., Gull Research Student at 

 Guy's Hospital. Communicated by Dr. PYE SMITH, F.R.S. 

 Received May 30, 1892. 



The process to be described depends upon the following facts : 



1. Ammonium urate is wholly insoluble in saturated solutions of 

 ammonium chloride. 



2. If solutions, such as urine, which contain the mixed urates of 

 different bases be saturated with ammonium chloride, the large 

 mass-influence of the latter ensures the rapid and complete conver- 

 sion of all the uric acid into biurate of ammonium, which, in accord- 

 ance with (1), is, pari passu, thrown out of solution. In the case of 

 urine, saturation with ammonium chloride is followed by a complete 

 precipitation of the uric acid present in the course of two hours at 

 most. 



