THE JOURNAL OF PHARMACOLOGY, 



/ = temperature. 

 ' b = barometric pressure reduced to o°C. 

 b' = tension of aqueous vapor at t. 

 0.0012566= weight of one cubic centimeter of nitrogen at o°C. and 760 



mm. pressure. 



The method as outlined above is rather expensive and not well adapted 

 for ordinary work. Various modifications, which however are all based 

 on the same principle, have therefore been devised. 



Among the more important modifications the following may be men- 

 tioned : 



A. Modification of Doremus : For the execution of this the Doremus 

 ureometer is employed. Fig. 2 illustrates the apparatus. The reagent 

 employed should in each instance be freshly 

 prepared. Its composition is as follows : A 

 stock solution of caustic soda, 100 grammes to 

 250 cc. of water. When wanted for use 10 cc. 

 of this solution are measured off, and i cc. of 

 bromine added. The bromine is measured off 

 by means of a nipple-pipette which accom- 

 panies each apparatus. Care must be taken 

 in handling the bromine since it gives off irri- 

 tating fumes. When dissolved the solution is 

 diluted with an equal volume of water and is 

 ready for use. 



The bulb of the instrument is filled 

 with the reagent and by inclining the 

 tube the long arm is filled to the neck of 

 the bulb. I cc. of the sample of urine 

 is measured off in the nipple-pipette and 

 slowly discharged into the long arm 

 containing the hypobromite solution 

 taking care not to force any air into the 

 apparatus. Rapid decomposition of the 

 urea takes place with evolution of ni- 

 trogen gas, which rises in the long arm 

 of the instrument, displacing the solu- 

 tion which flows out into the bulb. The 

 decomposition of the urea is complete in about 15 minutes, when the vol- 

 ume of nitrogen gas may be read off, indicating at once the quantity of 

 urea in the volume of urine tested. The instrument, according to its gra- 

 duation, indicates fractions of a gramme to the cubic centimeter, from o.oi 

 to 0.03 cm., or the number of grains of urea per fluid ounce of urine. It 

 also indicates by the signs + and — whether urea is present in increased 



Fig. 2. 



