284 METHODS OF IDENTIFICATION AND STUDY 



8. If the distillation of " B" is continued as long as 

 acid conies over (distilled water being occasionally 

 added to the distilling flask) the distillate can be 

 measured and 50 c.c. used for titration. This will 

 give the amount of volatile acid formation. 



9. The second part of the filtrate "B" (see page 

 282) should be examined for lactic, oxalic, succinic, 

 benzoic, salicylic, gallic and tannic acids, as follows : 



Ether Soluble Acids. 



1. Evaporate to a thin syrup, acidify strongly with 

 phosphoric acid. 



2. Extract with five times its volume of ether by 

 agitation in a separatory funnel. 



3. Evaporate the ethereal extract to a thin syrup. 



4. Add 100 c.c. water and mix thoroughly. 



5. To a small portion of this solution add slight ex- 

 cess of sodium carbonate, evaporate to dryness on the 

 water-bath, dissolve in 5-10 c.c. pure sulphuric acid, add 

 2 drops saturated copper sulphate solution, place in a 

 test-tube and heat in a boiling water- bath for 2 minutes, 

 cool, add 2 or 3 drops of the alcoholic thiophene and 

 warm gently. 



Cherry red colour = lactic acid. 



If a brown colour is produced on the addition of 

 sulphuric acid, another sample should be taken and 

 boiled with animal charcoal before evaporating. 



6. If lactic acid is definitely present, prepare zinc 

 lactate by boiling part of the solution of the ether extract 

 with excess of zinc carbonate, filtering and evaporating 

 to crystallise. The crystals so obtained have a char- 

 acteristic form, and if dried at 110 C., should contain 

 26.87 per cent, of zinc. 



7 . Test a portion of the rest of the solution of the ether 

 extract for oxalic acid (page 282, step 5). Carefully 

 neutralise the remainder and add ferric chloride solution. 



Red brown gelatinous precipitate = succinic acid. 



