464 BACTERIOLOGICAL CHEMISTRY 



the (-ase of mould action. It may be detected by .sohition 

 of the residue in hydrochloric acid, filtration, addition of 

 ammonia and acidification with acetic acid ; a precipitate 

 usually indicates the presence of oxalic acid, although 

 calcium fumarate or succinate are also possible. If the 

 latter are suspected the solution of the salt in hydrochloric 

 acid is extracted with ether in which fumaric and succinic 

 acids are soluble. Precipitation of the calcium salt on 

 boiling the aqueous solution usually denotes the presence 

 of citrate. 



The solution obtained by filtration or centrifugalisation 

 is submitted to the following treatment : — 



1. Volatile Neutral Products. — The solution is neu- 

 tralised with sodium carbonate and a portion distilled 

 off into a receiver cooled in ice. The distillate is tested 

 for : 



(a) Acetaldehyde, by addition of 2 : 4-dinitro -phenyl- 

 hydrazine hydrochloride ; .the yellow crystalline dinitro- 

 phenylhydrazone is recrystallised and its melting point, 

 162° C, determined. 



(6) Acetone, by making the 2 : 4-dinitro-phenylhydra- 

 zone, recrystallising and determining the melting point, 

 125° C. ; by saturation of the solution with solid 

 ammonium sulphate, addition of concentrated ammonia 

 solution and two or three drops of a freshly prepared 

 solution of sodium nitroprusside, when a purple colour 

 indicates the presence of acetone ; the iodoform test 

 may be carried out, using ammonia instead of sodium 

 hydroxide. 



(c) Ethyl alcohol, by the iodoform test ; or by oxida- 

 tion to acetaldehyde ; 25 ml. of the distillate is treated 

 with 0-1 g. of potassium dichromate and 0-5 ml. of 20 

 per cent, sulphuric acid and distilled slowly to collect 

 about 5 ml. of distillate which is tested for acetaldehyde ; 

 a green colour of the residue is confirmatory. 



