BY DR. LAUDER BRUNTON. 547 



flow in, at first rather rapidly, afterwards guttatim, until a per- 

 manent and dense cloud, not affected by vigorous stirring, 

 makes its appearance. 



The number of cubic centimetres used, multiplied by 0.010. 

 indicates the amount of chlorine, in fractions of a gramme, cal- 

 culated as NaCl, contained in 10 cubic centimetres of urine. 

 Thus, if 8.56 cubic centimetres of the standard solution of 

 chlorine were added, the quantity of Cl, calculated as NaCl, 

 in 10 cubic centimetres, would be 0.085 gramme. 



It must be remarked that if a urine contains albumin, this 

 substance must be removed by boiling and filtration before the 

 determination of chlorine by Liebig's method can be effected. 



194. Determination of chlorine by means of nitrate of silver. 

 In cases where the quantity of chlorine is exceedingly small, 

 the following method is much to be preferred to that already 

 described. 



Ten cubic centimetres of urine are placed in a platinum cap- 

 sule, together with 2 grammes of pure potassium nitrate (quite 

 free from chlorine), and evaporated to dryness. The residue is 

 ignited at a moderate heat until the whole of the carbon has 

 disappeared. 



The crucible is allowed to cool, and the saline mass which it 

 contains is dissolved in distilled water, a little nitric acid being 

 added. The estimation of chlorine may then be effected by 

 those methods which are to be found described in text-books 

 on chemical analysis. The chief of these methods consist () 

 in precipitating the chlorine as chloride of silver, etc., washing, 

 burning, and weighing the precipitate; and (6) in adding to 

 the neutralized solution of the chloride, mixed with a drop of 

 potassium chromate, a standard solution of nitrate of silver. 

 The nitrate of silver causes a white precipitate of chloride of 

 silver, when added to such a solution, until the whole of the 

 chlorine has been precipitated. Then, however, the addition 

 of a single drop more produces a deep salmon-red color, due 

 to the formation of silver chromate. 



** 195. Determination of the amount of Urea found 

 in Urine. 



I. By Liebig's Method. Tn order to determine the amount of 

 urea by Liebig's method, we require (a) baryta mixture as used 

 in the determination of the amount of Cl in urine, and (b) a 

 standard solution of nitrate of mercury, prepared in the same 

 manner as that used for Cl determinations, but containing 

 much more mercury. In making this solution, dissolve about 

 75 grammes of pure mercury in pure nitric acid, adopting all 

 the precautions previously suggested, and dilute to the volume 

 of one litre. 



In order to grade the solution of mercuric nitrate for urea, 

 we must pour into a beaker 10 cubic centimetres of a standard 



