262 THE BLOOD. [CH. X. 



operation. A test-tube holder should be improvised by holding a 

 piece of folded paper round the neck of the tube. This is held 

 obliquely and shaken vigorously during the boiling. In this way 

 loss by spurting can be avoided. When the fluid has been 

 concentrated to about 4 cc., another 10 cc. of the nitrate is 

 added and the greater part of the fluid boiled off again. When 

 the volume has been reduced to about 3 cc. add i gram, of pure 

 potassium sulphate and 2 drops of saturated copper sulphate. 

 Heat over a micro-burner, using a Folin's fume-absorber (p. 383). 

 A very small flame, not quite touching the tube, is better than a 

 large flame a few inches away. A screen to keep off draughts is 

 sometimes necessary. After a time the fluid goes nearly black, and 

 subsequently lightens in colour until it is a faint blue or green. 

 Heating must be continued for at least 5 minutes after this stage 

 has been reached. 



Remove the flame and allow to cool until the tube can be held 

 in the hand. Then add 10 cc. of distilled water and shake. If a solid 

 cake separates out, the tube must be cautiously heated until this has 

 completely dissolved. Transfer the contents to tube B of the 

 apparatus shewn in fig. 34. Wash out the tube with another 10 cc. 

 of distilled water, adding this to B. Wash out with 10 cc. of rectified 

 alcohol and connect up to the apparatus. Into tube G measure 

 10 cc. of standard sulphuric acid (about 0-04 N.), add 3 or 4 drops of 

 methyl red and connect the tube up to the apparatus, the tube being 

 immersed in a tall jar of cold water. Connect G to a suction pump 

 as shewn, and connect the condenser E to the water supply by the 

 lower end. Into C place some 40 per cent, soda, which has been well 

 boiled in open dishes to remove any ammonia. Start the pump so 

 that a gentle stream of air passes through the apparatus. Allow 

 some of the soda to run into the solution until it becomes alkaline, 

 as will be seen by the fluid becoming blue. Heat the solution with a 

 micro-burner, or a Bunsen with a rose-top, to boiling point. The 

 use of a rose-top minimises the risk of the tube cracking. The flame 

 should not play directly on the glass. The air current and the 

 boiling can be regulated to minimise the risk of splashing. The 

 distillation should be allowed to continue for 10 to n minutes. 

 Remove the flame, but do not stop the air current. Disconnect 

 the rubber joint at D and wash the inner tube of the condenser 



