466 BACTERIOLOGICAL CHEMISTRY 



with ether. Evaporation of the ether sohition to dryness 

 gives a crystalline residue of succinic acid or a liquid 

 residue of lactic acid. Succinic acid may be identified by 

 its melting point (183° C.) and acid equivalent. Lactic 

 acid may be detected by evaporation to dryness, solution 

 of the residue in alcohol, addition of concentrated sulphuric 

 acid and a drop of dilute copper sulphate solution, heating 

 on a boiling- water bath for a few minutes, cooling and 

 addition of an alcoholic solution of thiophen ; a cherry- 

 red colour indicates the presence of lactic acid. Lactic 

 acid may also be isolated and identified as the crystalline 

 zinc salt. Lactic acid may also be found among the 

 volatile acid products since it is somewhat volatile in 

 steam. It is not completely precipitated as the calcium 

 salt by 80 per cent, alcohol, the salt being somewhat 

 soluble. 



The test for 'pyruvic acid may also be described here. 

 With the sodium nitroprusside test, as carried out for 

 acetone, a vivid blue colour is given by pyruvic acid. 

 A second test is the addition of a few drops of an alcoholic 

 solution of guaiacol followed by concentrated sulphuric 

 acid to give a separate layer ; a carmine -coloured ring 

 at the junction indicates the presence of pyruvic acid. 



(6) Mould products. Oxalic, citric, gluconic, fumaric, 

 succinic and malic acids are the most common acid 

 products of fungi. The crystalline calcium salts may be 

 obtained. Oxalic acid may be tested for as described 

 above (p. 464). Gluconic acid may be readily character- 

 ised as its phenylhydrazide (m.p. 200° C). The calcium 

 salt of citric acid is less soluble in hot than in cold water, 

 and is precipitated from fairly strong solutions on boiling. 

 Citric acid may be identified by esterification with methyl- 

 alcoholic hydrochloric acid solution when the trimethyl 

 ester, m.p. 78-5° C, is formed, or by conversion into the 

 amide, m.p. 207° C. Fumaric acid may be extracted with 

 ether, crystallised and identified by its sublimation at 

 about 200° C. and acid equivalent. Malic acid is best 



