v] HYDROLYZING ENZYMES 63 



concentrate the filtrate on a water- bath. With the concentrated solution make the 

 following tests : 



(a) Add a few drops to a little boiling Fehling solution. Reduction immediately 

 takes place. 



(6) Make the phloroglucin, orcinol and furfural tests for pentoses, using a small 

 quantity only of the hydrolysis mixture for the tests. A positive result will be given 

 in each case. The pentoses, arabinose and xylose, are responsible for these reactions. 



(c) Add to some of the solution phenylhydrazine hydrochloride, sodium acetate 

 and a little acetic acid, and leave in boiling water for half an hour for the osazone test 

 [see Expt. 41 (d)\ A mixture of osazones will separate out, among which glucosazone 

 can be identified. 



(d) Concentrate the remainder of the solution and then add some nitric acid of 

 sp. gr. T15 (see Expt. 43). Evaporate down on a water-bath to one-third of the bulk 

 of the liquid and then pour into about 100 c.c. of water. A white microcrystalline 

 precipitate of mucic acid will separate out, either at once or in the course of a day or 

 two. This demonstrates the presence of galactose. 



PEC TIC SUBSTANCES. 



These substances are considered at this point since they are said to 

 constitute, in more or less intimate connexion with cellulose, the middle 

 lamella of cell-walls in many tissues. The pectic substances are fre- 

 quently found in the juices of succulent fruits in which the tissues have 

 disintegrated, such as red currants and gooseberries. They have been 

 isolated chiefly from fleshy roots, stems or fruits, as, for instance, from 

 turnips, beetroot, rhubarb stems, apples, cherries and strawberries. 



Recent work (Schryver and Haynes, 28) points to the fact that in 

 turnips, strawberries, rhubarb stems and apples, there is the same pectic 

 material, and it is possible that all such substances may be identical. 

 The compound isolated in the above case is of an acidic nature and has 

 been termed pectinogen. When pectinogen is treated with dilute 

 solutions of caustic alkali at ordinary temperatures, it is rapidly changed 

 into a second substance termed pectin, which is readily converted into 

 a gel under certain conditions. 



In the case of juicy fruits, such as currants and gooseberries, the 

 pectinogen can be precipitated as a gelatinous precipitate by adding 

 alcohol to the expressed juice. In the case of fleshy fruits, stems and 

 roots, the procedure is as follows. The tissues are thoroughly dis- 

 integrated in a mincing machine and pressed free from all juice in a 

 powerful press. The residue is then dried, finely ground, washed with 

 water and finally extracted with dilute ammonium oxalate solution in 

 which pectinogen is soluble. The extract is concentrated and the 



