148 § 90. SPECIAL METHODS OF ANALYSIS. 



a little beyond the sides ; weigh the substance out in a small 

 porcelain or platinum boat, and insert the boat in a glass 

 tube open at both ends, and drawn out and bent down at 

 one end ; put this glass tube in the copper tube of the wa- 

 ter-bath, immerse the end of the glass tube, that is bent 

 downwards, in a measured quantity of standard sulphuric 

 acid, and connect the other end with an apparatus from 

 Avhich dry hydrogen is evolved. Apply heat to the water- 

 bath, and when the desiccation is completed, remove the 

 boat, rinse the glass tube into the flask containing the 

 acid, boil the acid a little to expel carbonic acid, that 

 miofht have been carried over with the ammonia, and 

 titrate with soda solution in the usual manner (§ 45, c). 



e. For the estimation of the amount of solid substances 

 in a solution^ evaporate a measured or weighed quantity 

 on the water-bath, and dry the residue at the temperature 

 indicated in each particular case ; this temperature may 

 range all the way from 100° to 180° C. 



f. If the liquid contains other volatile matters besides 

 water, as in the case of urine, which may give off am- 

 monia when heated, put it in a porcelain or a platinum 

 boat, which has been previously about two-thirds filled 

 with coarsely pounded and Avell-washed glass or coarse 

 quartz sand, dried at 100°, and weighed, and carry on the 

 evaporation as in the case of a solid evolving ammonia 

 when heated {d). 



g. If the solution contains substances that are decom- 

 posed at a temperature above 100°, and yet it is difficult 

 to dry the residue left on evaporation of the liquid thor- 

 ouglily at that temperature, imbed the dish containing 

 the residue in sand that is heated to 100° C, put the 

 whole over a dish of concentrated sulphuric acid under 

 the receiver of the air-pump, and exhaust the air ; after 

 the sand has cooled, repeat the process with a fresh quan- 

 tity of heated sand, and so on as long as there is any loss 

 of weight. 



