THE JOURNAL OF PHARMACOLOGY. 3 



is then removed to a retort, being very careful to remove every portion of 

 it. From this point on the operation is conducted in the same manner as 

 in the Kjeldahl method for the determination of total nitrogen. 



2. Method of Knop-Hiifner : For the execution of this method a great 

 many modifications have been proposed, and many different apparatuses 

 are employed (ureometers, azotometers, etc.). These are all based on the 

 same principle as the original Hiifner apparatus, and it will not be neces- 

 sary to describe any of them in detail, as a full description and directions 

 for use usually accompany each apparatus. The Knop-Hiifner method is 

 not absolutely accurate, but recommends itself on account of the ease and 

 rapidity with which it may be executed. It is of particular value in such 

 cases where great exactitude is not a requisite. The method depends 

 upon the fact that urea when brought in contact with sodium hypo- 

 bromite (NaBrO) is decomposed into water, carbon dioxide and nitrogen 

 as follows : 



NH, - CO - NH, + 3NaBrO = sNaBr + N, + CO, + 2H,0. 



This decomposition takes place most readily in the presence of a con- 

 centrated alkaline solution. It is necessary to employ a strong alkaline 

 solution, as the loss of nitrogen is in inverse ratio to the strength of said 

 solution. The carbon dioxide which is liberated is absorbed by the excess 

 of alkali and the volume of nitrogen gas given off is measured. 



The reagent required is prepared as follows (Knop) : 50 grammes of 

 sodium hydrate are dissolved in 125 cc. of distilled water. To this solu- 

 tion 12.5 cc. of bromine are added at one time, keeping the mixture cool. 

 The reagent should be kept in a cool, dark place, but even then decom- 

 poses in a few days. It is preferably made fresh when wanted for use. 



This quantity of reagent (175 gm. of NaOH solution and 12.5 cc. of 

 bromine) is required when the Hiifner apparatus is used. 



Conditions required : In order to insure the best results the following 

 must be observed : 



1. The sample of urine employed should contain i % of urea. A more 

 concentrated sample should be diluted by adding the proper quantity of 

 distilled water to reduce it to i %. 



2. Before placing the urine in the apparatus, the part which received 

 this liquid should be perfectly dry. This may be accomplished by rins- 

 ing first with alcohol and then with ether. 



3. The sample of urine employed should be free from albumin and 



glucose. 



The apparatus employed is known as the Hiifner ureometer. It may 

 be briefly described as follows (Fig. i) : 



A glass cylinder {B) having a capacity of about 100 cc, and which is 

 contracted at each end, is connected with a small bulb (/^), having a 



