68 CARBOHYDRATES AND THEIR [CH. 



grouping) is the magenta-red coloration given by phloroglucin in the presence of 

 concentrated hydrochloric acid. 



Soak the tissue to be experimented upon with an alcoholic solution of phloro- 

 glucin and then add a drop or two of strong hydrochloric acid. The magenta-red 

 colour will be produced. 



As material, practically any lignified tissue may be used. Shavings from twigs 

 of any tree or shrub, e.g. pith and wood from the Elder (Sambucus nigra), will be 

 found useful : also shavings from a match ; straw, bran, coarse string, cheap white 

 paper, such as newspaper or white and pale-coloured papers used for wrappings. 



Make the phloroglucin test on good white writing paper. It should not give the 

 reaction since it is made from cellulose. 



Other phenols and their derivatives will also give colour reactions with lignin in 

 the presence of hydrochloric acid, but the colorations in most cases are not so much 

 developed as with phloroglucin (Czapek, 6). For this reason (though it is also possible 

 to use any of the lignified tissues suggested above) good results are obtained by using 

 strips of any cheap newspaper, since the reagents seem to penetrate this material 

 quickly. 



Soak strips of newspaper (or other material) in alcoholic solution of the following 

 substances, or such of them as are available, and then add a few drops of concen- 

 trated hydrochloric acid. It is useful to put the material on a white glazed tile or 



plate : 



Reaction 



Phenol blue-green coloration 



Resorcinol ... violet ,, 



Orcinol ... ... red- violet 



Catechol ... greenish-blue 



Pyrogallol ... blue-green 



Guaiacol ... yellow-green 



Cresol greenish 



a-Naphthol ... greenish 



Thymol ... green 



Indol ... ... cherry-red 



Skatol cherry-red 



It should be noted that strong hydrochloric acid alone will sometimes 

 give a red colour with woody tissues: this is due to the presence of 

 phloroglucin in the wood itself (see phloroglucin, p, 88). 



Expt. 74. Destruction of the lignin element in wood. Take some paper which gives 

 the phloroglucin reaction for lignin strongly and cut it up into pieces about an inch 

 square. Then boil the paper in some 1 % sodium hydroxide solution for a short time. 

 After washing well, put it into a flask or large test-tube with a few c.c. of bromine- 

 water and allow it to stand for an hour or two. Then wash again and heat in a 

 2 % solution of sodium sulphite. Wash free from sulphite, dry and test with 

 alcoholic phloroglucin solution and strong hydrochloric acid. No red colour, or very 

 little, will be produced. If a little red coloration is formed, the process should be 

 repeated until finally all the lignin reaction disappears, 



