86 NITEOGEN 



in about half an hour) 10 grammes of pure potassium sulphate are 

 added to the flask and about half a gramme to a gramme of anhydrous 

 copper sulphate (easily prepared by heating powdered blue vitriol in a 

 porcelain basin until it becomes quite white) ; the heating is then con- 

 tinued in the draught place, the flask being either placed in an inclined 

 position or a small funnel or watch glass being placed on its neck in 

 order to prevent loss by spirting. The contents of the flask should be 

 kept in constant ebullition, due care being taken to avoid frothing over, 

 which may occur in the early stages of the heating. The flask is best 

 supported upon a retort- stand ring, its neck passing through a smaller 

 ring, and it is advisable to periodically rotate the flask so that no frag- 

 ments of soil may escape the action of the acid, or rather of the acid 

 potassium sulphate. 1 When all black or brown colouration disappears 

 (generally in about 1-J to 2 hours from the time of starting the heating) 

 it is safe to assume that the reaction is completed. The flask is then 

 allowed to cool, about 50 cc. or more of distilled water added, and 

 a cork carrying a separating funnel, delivery tube and inlet tube for 

 steam is inserted, the arrangement being shown in the diagram, Fig. 5. 

 In the separating funnel is placed about 80 or 90 cc. of strong caustic 

 potash solution, made by dissolving " stick " potash in its own weight 

 of water and boiling the solution for some time to expel any possible 

 ammonia. This solution can be prepared in considerable quantities 

 and kept in a closely corked bottle. 



When the apparatus is fitted up as described, a measured quantity 

 25 cc. of decinormal sulphuric acid is run from a pipette into F 

 through G, the cork being loosened to allow of the escape of air. B 

 should be disconnected from A at the rubber joint E and the water in 

 B heated to boiling. In the meantime the 80 or 90 cc. of potash solu- 

 tion in C are allowed to trickle slowly and with frequent shaking, or 

 better, rotation, into A. The copper sulphate affords a good indication 

 of the amount required. When the solution is alkaline the copper is 

 precipitated as blue copper hydroxide, which, however, is usually 

 quickly converted into black copper oxide owing to the heat evolved 

 by the action of the potash on the sulphuric acid. Care should be 

 exercised, lest frothing takes place during neutralisation. When an 

 excess of potash has been added, the tap of the separating funnel is 

 turned off and steam from B is admitted by connecting with the rubber 

 tube at E. The lamp under A should only have a small flame, lest 

 bumping, due to the presence of the solid matter in the flask, be pro- 

 duced. The flame under B should be of such a size that the pressure 

 of the steam is sufficient to raise the water in the vertical tube some 

 8 or 10 in., due attention being, particularly at first, directed to 

 the prevention of frothing in A. The flask, F, should be surrounded 

 with cold water in order to condense the steam coming over. This 

 method works very satisfactorily and the ammonia is entirely driven 

 over in about half an hour, and there is little risk of bumping or suck- 

 ing back. 



1 The object of adding the potassium sulphate is to allow the temperature to be 

 raised to a higher point than is possible with sulphuric acid alone. Indeed, the liquid 

 in the flask at the end consists essentially of fused potassium hydrogen sulphate. 



