V] CARBOHYDRATES 67 



(6) excess of 5 % calcium chloride solution. In the first case a gel of pectin is formed : 

 in the second case a gelatinous precipitate of the calcium salt of pectin. 



To a further quantity of the pectinogen add excess of lime water and let it stand. 

 The gelatinous calcium precipitate will separate out in a short time. 



Expt. 68. Detection of the pentose group in pectinogen. Filter off the pectin gel 

 obtained in the last experiment and allow it to dry. Then test for the pentose group 

 by the orcinol, phloroglucinol and furfural tests (see Expt. 39). All results will be 

 found to be positive. 



The extraction of pectinogen, etc. in the above experiments can equally well be 

 <;arried out with other material, e.g. ripe gooseberries, raspberries and strawberries, 

 using exactly the same methods. 



Expt. 69. Preparation of pectinogen from Turnips. Take two full-sized turnips 

 and mince them finely in a mincing machine. Then wrap the mass in a piece of 

 strong unbleached calico and press out the juice as completely as possible in a press. 

 The juice contains little pectinogen and can be thrown away. The pressed mass is 

 then thrown into about 200 cc. of freshly prepared 0*5 ^1^ ammonium oxalate solution 

 heated to 80-90° C. on a water- bath and stirred to make a paste. The liquid is again 

 rapidly pressed out in the press. To the viscid extract an equal volume of 96% 

 alcohol is added, and the ammonium salt of pectinogen separates out as a voluminous 

 gelatinous precipitate. This is filtered off and, when pressed free from alcohol and 

 dried, can be used for tests as in the previous experiments. 



The gelatinization of pectinogen can also be brought about by certain 

 enzymes termed pectases which are found in the juices of various plants,^ 

 i.e. root of Carrot (Daucus Carota) and leaves of Lucerne (Medicago 

 ^ativa), Lilac (Syringa vulgaris) and Clover (Trifolium pratense). 



Expt. 70. Action of pectase on pectinogen. Make an extract of either Lucerne or 

 Olover leaves by pounding them in a mortar with a little water, and then filter. Add 

 the filtrate to some of the pectinogen solution prepared in Expt. 66 or 69. On 

 standing a gelatinous precipitate will be produced. Should the reaction be slow, it 

 may be accelerated by placing the mixture in an incubator. 



Celluloses. 

 Celluloses are very important polysaccharides. They form constituents 

 of the structural part of all the higher plants. The cell-wall of the young 

 cell consists entirely of cellulose, but in older cells the walls may be 

 lignified, cuticularized, etc., i.e. the cellulose may be accompanied by 

 other substances such as lignin, cutin, mucilage, etc. In the light of 

 these facts the term cellulose is made to include: 



1. Normal celluloses. 



2. Compound celluloses. 



(a) Ligno-celluloses. 

 (6) Pecto-celluloses. 

 (c) Adipo- or cuto-celluloses. 



3. Pseudo- or Reserve celluloses. 



5—2 



