606 SUMMARY OF OTTRRENT RESEARCHES RELATING TO 



tte use of diagrams of microscopical objects for class teaching. These 

 diagrams are made in the usual manner with chalks, charcoal, and pig- 

 ments. The only novelty in the paper is the suggestion that time may 

 be saved by obtaining the image of an illustration in a book by placing 

 the leaf in a magic lantern and throwing the image on the drawing 

 paper. 



Thallin, a new reagent for Lignin.* — The otherwise excellent re- 

 agent for lignin, phloroglucin, has the disadvantage that the stained 

 preparations rapidly become colourless on exposure to light. Herr E. 

 Hegler proposes as a substitute thallin, which is an extraordinarily 

 delicate reagent for lignified tissue, is of very easy application and 

 great persistence under the action of light, and possesses the additional 

 advantage of presenting no reaction with coniferin. The section is 

 placed first in pure alcohol, and then, in a watch-glass, in a concen- 

 trated solution of thallin -sulphate in dilute alcohol ; all the lignified 

 parts then assume a dark orange-yellow colour, which increases with the 

 length of the immersion, and is not lost after exposure to the light for 

 months, while the cellulose and cork membranes remain perfectly 

 colourless. With long immersion the cellulose and cork tissues assume a 

 slight rose colour. 1 ccm. of a 1 per cent, solution, containing 0*001 gr. 

 of thallin-sulphate, produces a strong reaction with pine-wood ; and this 

 is by no means the limit of the sensitiveness. With regard to the 

 reaction of the various lignin-reagents on the two substances which are 

 the constant associates of lignified tissues, vanillin and coniferin, — thallin 

 reacts with vanillin but not with coniferin, phenol-hydrochloric acid 

 with coniferin but not with vanillin, all the other lignin-reagents with 

 both. 



New micro-chemical reagent for Tannin.j — According to M. L. 

 Braemer there are objections to all the reagents at present used for the 

 detection of tannin ; ammonium molybdate has the disadvantage that its 

 precipitates with tannic acid are soluble in water and dilute acids, and 

 the reagent itself has but little persistency. The author proposes as a 

 substitute a mixture of 1 gr. sodium tungstate and 2 gr. sodium acetate 

 in about 10 ccm. of distilled water, which precipitates both tannic and 

 gallic acid, but cannot be used to distinguish between these two. It 

 does not precipitate albuminoids, nor other substances resembling tannin. 

 By this reagent the presence of • 00001 gr. of gallic acid can be detected. 



Tests for Tannin.J — In the account of his researches on the presence 

 and distribution of tannin in the vegetable kingdom,§ Herr H. Moeller 

 thus classifies and comments on the various chemical tests used for this 

 STTbstance. 



(1) Iron-salts.— The great objection to the use of these reagents is 

 that the compounds of iron and tannic acid are readily soluble in excess 

 of the reagent, in weak acids, or in alkaline liquids. The last the author 

 has observed only in the case of Tussilago Farfara, while in many cases 

 the compounds in question are soluble in acids, especially in hydro- 



* SB. Bot. Ver. Munchen, March 11, 1889. See Bot. Centralbl., xxsviii. (1889) 

 p. 616. 



t Bull. Soc. Hist. Nat. Toulouse, 1889, Jan. 23, 4 pp. See Bot. Centralbl., 

 xxxviii. (1889) p. 820. 



X Ber. Deutsch. Bot. GcsolL, vi. (1889) Gen.-Versamml.-Heft, pp. Ixvii.-lxxi. 



§ Cf. ante, p. 541. 



