20 PRACTICAL BOTANY. 



it is treated with sulphuric acid, are characteristic 

 The cellulose reaction is also given with the chloride of 

 zinc mixture. 



IV. Inorganic salts. 



Sodium chloride (common salt). This is used both 

 in dilute (10 per cent.), and in saturated solution in 

 water as a solvent for the proteid crystalloids. 



The 10 per cent, solution is used for producing 

 plasmolysis. 



Ferrous sulphate. Used in dilute solution in water, 

 to which a drop of nitric acid has been added, as a test 

 for tannin. 



Potassium bichromate. Used in dilute solution 

 in water as a test for tannin ; used also (in 1 per cent, 

 aqueous solution) for hardening tissues. 



Potassium chlorate.^Used, together with nitric 

 acid, as a macerating agent. 



Copper sulphate. Used in very dilute solution 

 in water ; the blue colour of the solution must be only 

 just perceptible. It is used, with potash, as a test for 

 some kinds of sugar, and for proteids. It is used also in 

 the preparation of ammoniacal solution of cupric hydrate, 

 which dissolves pure cellulose. For the preparation of 

 Fehling's fluid the following directions are given in 

 Foster's Practical Physiology : 



(a). Dissolve 34'65 grm. of pure crystallised cupric sulphate in 

 about 160 c.c. of distilled water. 



(&). Dissolve also 173 grm. of pure crystallised potassic-sodic 

 tartrate in 600 to 700 grm. of sodic hydrate sp. gr. 1.12. 



Add (a) to (b) stirring well to cause a thorough mixture, and 

 dilute with distilled water to a litre. 



Fehling's fluid should be fresh made whenever it is required, 

 since it decomposes on keeping ; it will keep some little time if 



