ZOOLOGY AND BOTANY, MICROSCOPY, ETC. C07 



chloric acid. Chloride of iron exhibits osmose freely in a dilute 

 aqueous solutiou, but always has an acid reaction ; when dry and dis- 

 solved in absolute ether, it is an exceedingly good reagent for tannin. 

 Acetate of iron in the form of either liquor ferri acctici or tinclura 

 ferri acctici gives a beautiful reaction ; the former diffuses with great 

 difficulty ; the latter is preferable in many respects. Citric iron- 

 ammonium oxide can only be used in a few cases, in consequence of its 

 very slight ditt'usibility. 



(2) Of oxidizing reagents, potassium bichromate gives a beautiful 

 chestnut-brown precipitate. Its comiiaratively slight dili'usibility can be 

 increased by the addition of a few droi)S of acetic acid. It is probable 

 that one product of the oxidation of tannin is purpuro-gallin or an allied 

 substance, but the author believes that there are several kinds of purpuro- 

 gallin, and that these result from the oxidation of different tannin acids 

 in the plant. Ammonium molybdate (Gardiner's reagent) is the one 

 recommended by the author as the best. It may be slightly alkalized 

 by ammonia in order to increase its diffnsibility ; and the remaining cell- 

 contents are then for the most part left unchanged. Dilute aqueous 

 solutions of alkalies oxidize indirectly by the production of oxygen ; but 

 these reagents cannot be recommended, neither can the reaction with 

 iodine. 



New method of recognizing- small quantities of Invertin.* — Accord- 

 ing to M. J. Costautin, Bacillus phosphor esc ens Hermes {Micrococcus 

 phosphorescens Cohn, M. Pfliigeri Ludwig), which is found on salt fish, 

 possesses a phosphorescent property when it de vol opes in glucose, but it 

 loses this in the presence of saccharose. This property serves to detect 

 invertin in small quantities. A decoction of the fish in sea-water is 

 prepared, and 7 per cent, of gelatin added, which is mixed with the 

 culture of the above mentioned bacillus. After coagulation there 

 remains a luminous substratum ; this, at the end of two or three days, 

 shows great sensitiveness towards chemical agents. If saccharose be 

 added to the gelatin, the luminosity does not change ; but if a trace 

 of invertin be added, it quickly forms a large luminous plate on the 

 substratum. 



* " J. 0." in Morot's Journ. de Bot., ill. (18S9) p. 32. 



