M. RAFAELLE PIR1A ON POPULIN. II.-On Populin. BY RAFAELLE PIRLA. (FROM A LETTER TO DR. HOFMANN.) Since my return to Italy I have been engaged with the investiga- tion of a crystalline substance discovered as you will recollect by Braconnot in the leaves and bark of Populus tremula and described by this chemist under the name of Poplin. The composition and the reactions of this compound have remained unknown up to the present moment. From the following note which gives you the results I have as yet obtained you will see that populin is closely con- nected with several of the best known series of organic chemistry. The composition of populin is represented by This formula the result of direct analysis is moreover confirmed by the deportment exhibited by this substance when submitted to the influences of chemical agents.On heating populin with dilute acids it is decomposed into benzoic acid grape-sugar and saliretin and you will observe that the above formula of crystallized populin exactly represents the sum of the elements of one equivalent of each of these substances. c4 Hg 020 = ci4 H6 O4 f c12 '14 -k c14 H6 '2. -L--y---J L-vLL-A Crystallized populin. Benzoic acid. Grape-sugar. Saliretin. Since saliretin is a product of the action of acids on saligenin populin may be viewed as a conjugate compound of benzoic acid with saligenin and grape-sugar. -' O, '14 '4 H6 3.'1 '14 f '14 '4 = '40 H,6 c-.--v-,J Ly-J L7-J LPT-J Crystallized populin. Benzoic acid. Grape-sugar.Saligenin. or what amounts to exactly the same thing as a conjugate compound of benzoic acid with salicin itself O14 + 'IH[O* 3-c26 c*O H26 O20 = '14 H6 '4 L-+.-J L-2 L-y-) Crystallized populin. Benzoic acid. Salicin. The relations which I have pointed out induced me to try whether M. RAFAELLE YIlEIA ON POPU'LISI populin might not be converted into salicin. Nothing in fact is easier it suf€icesto boil a solution of populin with baryta-water j you obtain a perfectly limpid liquid which contains nothing except ben- zoate of baryta and salicin. I have compared the chemical and physical properties of salicin thus obtained with those of the sub- stances prepared from willow bark; they coincide in every point. Here then we have a very coniplex organic compound artificially produced by the decornposition of a still more complex substance.My next step will be to transform if possible salicin into populin; I hope to effect this change by submitting it to the action of chloride of benzoyl. C, 01 + C,* H 0 C1= C, HZ2 01 + HCL c-___y----J L-r---l-%---J Salicin. Chloride of benzoyl. Populin (anhydrous). The only difficulty which presents itself as get is the action of the hydrochloric acid which is liberated in this processt on the newly- formed compound I need scarcely mention that in boiling populin with a mixture of sulphuric acid and bichromate of potassa you obtain a considerable quantity of hydride of salicyl.