168 ESSENTIALS OF CHEMICAL PHYSIOLOGY 



Of the two raethods just described, Liebig's is so cumbrous and inexact 

 that it has almost passed out of use. The hypobromite method holds its own, 

 as it is easy and sufficiently exact for clinical purposes. When absolute 

 accuracy is necessary, one of the numerous recently introduced methods 

 must be employed, and of these the method of Morner and Sjoqvist appears 

 to be best. 



(c) Method of Morner and Sjoqvist. — The following reagents are neces- 

 sary : 



i. A saturated solution of barium chloride containing 5 per cent, of 

 barium hydrate. 



ii. A mixture of ether and alcohol in proportion 1 : 2. 



iii. The apparatus, &c., necessary for carrying out Kjeldahl's method of 

 estimating nitrogen (see p. 199). 



Analysis. — Five c.c. of urine are mixed with 5 c.c. of the barium mixture 

 and 100 c.c. of the mixture of ether and alcohol. By this means all nitrogenous 

 substances except urea are precipitated. Twenty-four hours later this is filtered 

 off, and the precipitate is washed with 50 c.c. of the ether-alcohol mixture, 

 the filter-pump being used to accelerate the process. The washings are 

 added to the filtrate ; a little magnesia is added to this to drive off ammonia, 

 The alcohol and ether is then driven off at a temperature of 55° C. and 

 evaporation is continued at this temperature until the volume of the residue 

 is 10-15 c.c. The nitrogen in this is estimated by Kjeldahl's method. The 

 nitrogen found is multiplied by 2'143, and the result is the amount of urea, 



PREPARATION OF UREA FROM URINE 



(1) Evaporate the urine to a small bulk. Add strong pure nitric acid in 

 excess, keeping the mixture cool during the addition of the acid. Pour off 

 the excess of fluid from the crystals of urea nitrate which are formed ; strain 

 through muslin and press between filter paper. Add to the di-y product 

 barium carbonate in large excess. This forms barium nitrate and sets the 

 urea free. Mix thoroughly with sufficient methylated spirit to form a paste. 

 Dry on a water-bath and extract with alcohol; filter ; evaporate the filtrate 

 on a water-bath and set aside. The urea crystallises out, and may be de- 

 colorised by animal charcoal and purified by recrystallisation. 



(2) The following method is well adapted for the preparation of micro- 

 scopic specimens of urea and urea nitrate : Take 20 c.c. of urine ; add 



aryta mixture ' (two volumes of barium hydrate solution and one volume 

 of barium nitrate solution, both saturated in the cold) until no further preci- 

 pitate is produced ; filter, evaporate the filtrate to a thick syrup on the 

 water- bath, and extract with alcohol ; pour off and filter the alcoholic 

 extract ; evaporate it to dryness on the water-bath and take up the residue 

 with water. Place a drop of the aqueous solution on a slide and allow it to 

 crystallise ; crystals of urea separate out. Place another drop on another 

 slide and add a drop of nitric acid ; crystals of urea nitrate separate out. 



ESTIMATION OF CHLORIDES 



The chlorides in the urine consist of those of sodium and potassium, the 

 latter only in small quantities. The method adopted for the determination 



