XIX.] 



VOLUMETRIC ANALYSIS FOR UREA. 



123 



nitrogen by this process; further, that only about 92 per cent, 

 of the N of tlie urea is given off in the above processes. These 

 sources of fallacy are. however, taken into account in graduating 

 the apparatus. 



6. Steele's Apparatus (fig. 63). — In this apparatus the collect- 

 ing tube is a graduated burette graduated in cc. 



(a.) Use tliis apparatus in a similar manner. The tube B is 

 intioduced into the flask A by means of a 

 pair of forceps. ^k 



(b.) Eead off the number of cc. of N ' ' 

 evolved, and from this calculate the 

 amount of urea. Every 35.4 cc. N = o.i 

 gram urea. 



7. Ureameter of Doremus (fig. 64). — 

 It consists of a graduated bulb-tube, closed 

 at one end. Hypobromite of sodium 

 solution is poured into the tube up to a 



certain mark. 



to 



I 



and diluted with water 

 fill the long arm and bend. The urine 

 to be tested is drawn into the pipette to 

 the graduation. The pipette is then passed 

 into the ureameter, as far as the bend, 

 and the nipple is compressed slowly. The 

 urine will then rise through the hypo- 

 bromite solution, and the gas evolved will 

 collect in the upper part of the tube. 



Pkch division indicates .001 gram of 

 urea in i cc. of urine. The percentage of urea present in the urine 

 is found by simply multiplying the result of the test by 100. 



8. Study also Charteris's apparatus. The bromine and caustic soda are 

 mixed in a marked measure, so that the hypobromite is always fresh, while 

 tlie collecting tube for the N is so graduated as to indicate a certain percentafe 

 of urea. ^ 



¥lQ. 64. 



Ureameter of Doremus 

 with Pipette, 



9. Study Squibb's apparatus. 

 with the apparatus. 



In all these cases directions are supplied 



10. Liebig's Volumetric Process for Urea with Sodic Carbonate as Indi 

 cator, — I cc. of the SS. (mercuric nitrate) = .01 gram or 10 milligrams of urea. 

 This method has been largely supplanted by the hypobromite process. 



11. Solutions Required. 



Baryta Mixture.— Prepared as in Lesson XIX. 12 (r). 



Mercuric Nitrate Solution.— (i cc. = -qi gram urea). Dissolve with the 

 aid of gentle heat 77.2 grams of pure dry oxide of mercury in as small a 

 quantity as possible of HNO3, evaporate to a syrup, and then dilute with 



