CH. IX] DECOMPOSITION. 247 



under reduced pressure can be readily constructed with 

 distilling flasks and a Liebig's condenser. The diagram 

 Fig. 45 shows such an apparatus with the parts connected 

 ready for distilling. Care must be taken that all the con- 

 nections are air-tight. 



Changes occurring in solutions on keeping. 



It is necessary that the examination of the solutions 

 obtained by dissolving in water the residue from the 

 alcohol extract (II.), by extracting with cold water (III.), 

 and dilute acid (IV.), etc., should be examined as soon as 

 they are prepared. 



Such solutions undergo change very rapidly from the 

 action of micro-organisms, and in a few days will often be 

 full of fungoid growths. If the solutions have to be put 

 aside before they can be examined, some strongly anti- 

 septic substance must be added to prevent such growth. 

 Chloroform is very convenient, as it can be readily 

 expelled by warming before the examination is made. 

 The addition of 1 c.c. of chloroform per liter of extract 

 will generally be found sufficient. 



Small quantities of thymol may also be used for this 

 purpose the small amount of thymol necessary will not 

 interfere with the subsequent examination, but its use is 

 not applicable where any part of the solution is to be 

 used for fermentation (see sugars). 



If the alcoholic or cold-water extract is found to be 

 acid in reaction when first prepared it should at once be 

 exactly neutralised, because heating with acids may cause 

 changes in some of the constituents (e.g. cane-sugar may 



