546 THE SECRETIONS. 



to decompose 0.200 gramme of NaCl. As it is convenient to 

 have a solution of which 10 cubic centimetres shall be equiva- 

 lent to 0.100 gramme of NaCl, we must take our solution and 

 dilute it to the required extent. In the assumed case, 12.7 

 cubic centimetres Contained as much of the mercurial salt as 

 correspond to 0.200 gramme of NaCl, ?'. e., as much as would 

 be required in 20 cubic centimetres of solution. If we there- 

 fore diluted 12.7 cubic centimetres with 7.3 cubic centimetres 

 of water, we should obtain 20 cubic centimetres of a solution 

 of which 10 cubic centimetres would be exactly capable of de- 

 composing 0.100 gramme of NaCl. 



But as in preparing such a standard solution we deal with 

 large quantities of fluid, it is well to effect the dilution of the 

 whole at once. 



Thus let us suppose that we have 800 cubic centimetres of 

 the solution, of which 12.7 cubic centimetres are equivalent to 

 0. _><><> gramme of NaCl. 



As 12.7 cubic centimetres require the addition of 7.3 cubic 

 centimetres of water, it is easy to find how much 800 cubic 

 centimetres require, viz., 459.8 cubic centimetres. If we then 

 measure out very accurately this quantity of distilled water, 

 and :ul<l it to our solution, we obtain 1259.8 cubic centimetres 

 of a solution of which 10 cubic centimetres represent 100 milli- 

 grammes of NaCl, or 60.65 milligrammes of 01. 



Having made the standard solution of nitrate of mercury 

 for the estimation of chlorine, we must, before analyzing urine, 

 prepare a solution which we shall designate as Karyta Mixture. 



This is prepared by mixing two volumes of a solution of 

 barium nitrate, saturated in the cold, with one volume of a 

 solution of caustic baryta (barium hydrate), similarly saturated. 



Two volumes of the urine to be analyzed (say 40 cubic centi- 

 metres) are now mixed with one volume (say 20 cubic centi- 

 metres) of baryta mixture. An abundant precipitate falls, 

 consisting chiefly of a mixture of phosphate, sulphate, and car- 

 bonate of barium. (This removal of phosphates is essential, 

 as these salts are precipitated by the solution of nitrate of 

 mercury.) 



The fluid in which the precipitate has formed is filtered, care 

 being taken that the filter is not moistened. 



As the filtrate contains one-third of its volume of baiyta 

 mixture, it is convenient to take for analysis 15 cubic centi- 

 metres. This quantity will exactly correspond to 10 cubic cen- 

 timetres of urine. It is convenient, therefore, to have, in addi- 

 tion to- pipettes graduated so as to deliver 20 and 40 cubic 

 centimetres, one which delivers exactly 15 cubic centimetres 

 of fluid. The measured portion of filtrate is very slightly 

 acidified by adding, drop by drop, exceedingly dilute nitric 

 acid, and then the solution of nitrate of mercury is allowed to 



