2 THE JOURNAL OF PHARMACOLOGY. 



(b) Modification of Morner and Sjoqvist. 



These observers found that under certain conditions phospho-molybdic 

 acid also precipitates urea, at least in part. They recommend a method 

 which obviates the necessity of estimatmg the preformed ammonia. 



B. Method of Knop-Hiifner : This is based on the following principle : 

 Urea is decomposed when treated with an alkaline solution of sodium 



hypobromite into nitrogen, carbon dioxide and water, as follows : 



NH2-CO-NH2+3NaBrO = 3NaBr+N2+C02+2H20 



The carbon dioxide is fixed by the excess of alkali present, and the nitro- 

 gen is collected and measured in a properly constructed apparatus. One 

 gramme of urea furnishes theoretically 370 cc. of nitrogen at O °C. and 

 under a pressure of 760 mm. 



C. Method of E. Riegler : This method is based on the fact as already 

 shown by Grehant. Boymont, that urea when treated with Millon's re- 

 agent is decomposed into equal volumes of carbon dioxide and nitrogen. 

 The gases are collected and from their combined volume the quantity of 

 urea is calculated. Riegler employs for the execution of his method a 

 specially constructed apparatus, which is accompanied by tables, which 

 show the quantity of urea for any given volume of gas at any certain tem- 

 perature and pressure. The method is a rapid one and fairly accurate. 

 It is not as expensive as that of Knop Hiifner, 100 cubic centimeters of 

 the reagent sufficing for about 40 determinations. The reagent does not 

 decompose upon standing, as does the alkaline hypobromite solution, this, 

 of course, being a further advantage. The necessity of purchasing a 

 specially constructed apparatus is, however, a serious disadvantage. 



Most of these methods are not applicable for general purposes, as their 

 execution requires considerable skill and practice, otherwise the results 

 obtained will be far from accurate. On this account the methods of Hor- 

 ner and Sjoquist, and Knop-Hiifner only will receive attention here. 

 I. Method of Morner and Sjoquist : 5 cc. of urine together with 5 cc. of 

 a saturated solution of barium chloride, in which 5 per cent, of barium 

 hydrate is dissolved, are placed in a flask. To this mixture is added 100 cc. 

 of a mixture of 2 parts of 96 per cent, alcohol, and i part of ether. The 

 flask is then stoppered and set aside for a period of 12 hours. The object 

 of this procedure is to cause a precipitation of all the nitrogenous constitu- 

 ents of urine except uiea. After standing for the required time, the pre- 

 cipitate which has formed is collected in a filter, and washed with alcohol 

 and ether, mixed in proportion as above indicated. The filtrate is con- 

 centrated at a temperature not exceeding 6o°C. to a volume of 20-25 cc. 

 A little >^ater and calcined magnesia are now added and the concentration 

 continued, for the purpose of removing preformed ammonia, until the va- 

 pors given off are no longer alkaline in reaction. The concentrated liquid 



