RADIX RHEI. i[)9 



As to the contents of the white cells, they are loaded either with 

 starch or tufted crystals of oxalate of calcium, the amount of the latter 

 being especially liable to variation. Scheelc, after having discovered the 

 oxalic acid, pointed out in 1784 that the crystals under notice consist 

 of that acid in combination with lime; he was the first to point out the 

 true composition of those crystals which are of so wide a distribution 

 throughout the vegetable kingdom. The medullary rays contain the 

 substances peculiar to rhubarb, but none of them occur in a crystalline 



state. 



Chemical Composition. — The active constituent of the root lias 

 long been supposed to reside in the yellowish red contents of the medul- 

 lary rays. Schrader as early as 1 807 prepared a Bhuharh- Bitter, to which 

 he attributed the medicinal powers of the drug. Since then several sub- 

 stances of the same kind have been separated by various methods, and 

 described under different names: such are the Rhaharherstoff oiTromms- 

 dorff, the Rheiimin of Hornemann, the Rhaharherin of Buchner and 

 Herberger, the Rhuharh-Yelloiu or Rheln, and the RJiaharharic Acidof 

 Brandes. 



Schlossberger and Dopping in 184-i first recognized among the above- 

 named substances a definite chemical body named Chrysoijhan or Chryso- 



Vhanic Acid, C"ff | S)h^2^^' ^^^^^^ ^^^^ ^^^^ ^^^^^ ^^ ^^^^ ^'^ ^^^^' 

 leder and Heldt in the yellow lichen, Parmelia imrietina. It partly 

 forms the yellow contents of the medullary rays of rhubarb, and when 

 isolated crystallizes in golden yellow needles or in plates. It dissolves 

 in ether, alcohol, or benzol; though scarcely soluble in water, it is 

 nevertheless extracted from the root to some extent by that solvent, 

 probably by reason of some accompanying substance. Alkalis dissolve 

 It, forming fine dark red solutions. Chrysophan, O'R''0\ is a deriva- 

 tive of anthracene, C"!!"', and closely allied to alizarin, C'H O . 



By precipitating alcoholic solutions of extract of rhubarb with ether, 

 Schlossberger and Dopping obtained, together with chrysophan, resinous 

 bodies which they n^mec^ Ajjoretin, Phceoretin and Erythrorehn.^ 



Be la Rue and Muller (1857) extracted from rhubarb, m addition to 

 chrysophan, an allied substance, JSmodin, which crystallizes in orange- 

 coloured prisms, sometimes as much as two inches long. Its constitu- 

 tion was subsequently found to agree with the formula C"H' | (^q-q^^^- 



. Kubly (1867) has obtained from rhubarb the following con- 

 stituents : 



1. Meo-tannic Acid, C2«H2«0^^ a yellowish powder abundantly pre- 

 sent in rhubarb, soluble in water or alcohol, not in ether, -^t^ «°^3^^ 

 produce blackish green precipitates with persalts of iron, and greji.n 

 ones slowly turning blue, with protosalts of the same. ,,aa:^u 



. 2. Rkeamk Acid (EheumsLre) , C^^H^^O^ obtained as a redcb^h- 



brown powder, by boiling rheo-tannic acid with ^.^^1"^%™'"^;^^, ^^^^^^^ 

 a fermentable sugar beinS developed at the same time. . . ^^^"^Vf ^"^, 

 ^-^iHbits nearly the same reactions as rheo-tannic acid, but is vcij 

 sparingly soluble in cold water. It partly pre-exists in rhubarb 



3. Neutral colourless substance, sparingly soluble m ^^t J^ St,?o7. 

 separating from the latter in prismatic crystals of the formula O il U , 



