36 PRACTICAL ORGANIC AND BIO-CHEMISTRY 



With a pipette a quantity of standard sulphuric acid (5 c.c. of N 

 or 50 c.c. -iN H 2 SO 4 ) are measured out into a clean beaker or flask 

 (preferably conical) of about 600 c.c. capacity, and this is placed below 

 the condenser so that the end of the condenser just reaches the surface 

 of the liquid It is preferable to add a few drops of indicator, methyl 

 orange or alizarin red, 1 before the distillation is commenced in case 

 more acid is required than that originally taken ; the change in colour 

 of the indicator gives notice of this fact. 



Sometimes the distillation is carried out without using a condenser 

 (Fig. 19, No. 2) ; the end of the special distilling tube is then dipped into 

 the standard acid. There is in this case usually greater danger of the 

 liquid being sucked back into the flask which is being distilled, and 

 further the glass is attacked by the ammonia with liberation of alkali, 

 which causes inaccuracies in the determination. 



No. i. No. 2. 



FIG. 19. 



The round-bottomed flask is removed, a piece of porous earthenware 

 is added and excess of caustic soda solution (50 c.c. of 40 per cent, 

 for every 10 c.c. concentrated H 2 SO 4 used) is run in under the dilute 

 acid without mixing. The flask is connected again to the condenser 

 seeing that all corks fit tightly. The soda and acid are mixed and 

 the ammonia is distilled off into the acid. In about half an hour the 

 ammonia will have completely passed over into the standard acid To 



1 Cochineal, congo red and other indicators may also be used, or the titration may be 

 effected using sodium iodate and potassium iodide and standard thiosulphate solution 

 (P- 563). 



