60 HOW CROPS GROW. 



The liquid, after separating excess of lime and adding 

 acetic acid, is mixed with alcohol,, whereupon arabin is 

 precipitated. Arabin, thus prepared, is a milk-white 

 mass which, while still moist, readily dissolves in water 

 to a mucilage. It strongly reddens blue litmus and ex- 

 pels carbonic acid from carbonates. \Vhen dried at 212 

 arabin becomes transparent and has the composition 

 Ci 2 H 22 Oii. Dried at 230 it becomes (by loss of a mole- 

 cule, of water) C 12 H 2 o0 10 , or 2 C 6 H 10 5 . 



Arabin forms compounds with various metals. Those 

 with an alkali, lime, or magnesia as base are soluble in 

 water. Gum arabic, when burned, leaves 3 to 4 per cent 

 of ash, chiefly carbonates of potassium, calcium and mag- 

 nesium. Arabic acid, obtained by Fremy from beets by 

 the foregoing method, but not in a state of purity, was 

 described by him as "metapectic acid." To Scheibler 

 we owe the proof of its identity with the arabin of guni 

 arabic. 



Metarabin. When arabin is dried and kept at 212 

 for some time, it becomes a transparent mass which is no 

 longer freely soluble in water, but in contact therewith 

 swells up to a gelatinous mass. This is designated 

 metarabin by Scheibler. It is dissolved by alkalies, and 

 thus converted into arabates, from which arabin may be 

 again obtained. 



The body named pararalin by Reichardt, obtained 

 from beet and carrot pulp by treatment with dilute hy- 

 drochloric acid, is related to or the same as metarabin. 

 Fremy's "pectin," obtained by similar treatment from v 

 beets, is probably impure metarabin. 



' EXP. 34. Reduce several white turnips or beets to pulp by grating. 

 Inclose the pulp in a piece of muslin, and wash by squeezing in water 

 until all soluble matters are removed, or until the water comes off 

 nearly tasteless. Bring the washed pulp into a glass vi-rl. with 

 enough dilute hydrochloric ar-id < 1 part by bulk of commercial muriatic 

 acid to 15 parts of water > to saturate the mass, and let it stand 4* hours. 

 Squeeze the acid liquid, filter it, and add alcohol, when " pectin 

 separate. 



