J. C. Marquart's Report of the Progress of photochemistry. 333 



prepared and becomes brown, in the same manner as iron 

 when touched with zinc, but slowly, and, so to speak, with 

 resistance. But if it be prepared and touched alternately 

 several times in succession, it finally becomes subject to in- 

 termittences of action, becomes heated, and emits torrents of 

 gas, without there being any possibility of calming the effer- 

 vescence. 



Since these experiments were made, I have found a very 

 curious memoir by Keir, in the Transactions of the Royal 

 Society of London for the year 1790, entitled, Experiments 

 and observations on the dissolution of metals in acids, and their 

 precipitatio?is ; in which several facts of this kind are recorded. 



Keir was led to remark the prepared state of iron, when 

 studying the precipitation of silver by that metal, in which 

 Bergman had previously found some anomalies. He even 

 discovered that this singular state may be developed by the 

 action of nitrous acid. But the remarkable effects arising 

 from contact with other metals, by which these facts may be 

 included in the class of electro-chemical phenomena, escaped 

 his observation. That the contact of one metal should pro- 

 tect another from the action of a chemical agent, as long as 

 the contact lasts, does not now surprise us; (it occurs when 

 nitric acid is poured over a piece of copper placed upon pla- 

 tina;) but what to me appears extraordinary in the experi- 

 ments above described is, that the effect can be indefinitely 

 prolonged after the contact ceases ; and that a permanent elec- 

 trical state may exist on the surface of a metal, and be there 

 maintained by its own power, contrary to that which ordi- 

 narily exists in the same metal, and to that which continues to 

 exist in it at a very small depth in its interior, even during 

 the existence of the forced state at the surface. 



Slough, Aug. 19, 1833. 



XLI. A Beporton the Progress of Photochemistry in the Year 

 1835, in reference to the Physiology of Plants. By J. C. 

 Marquart.* 



[Continued from vol. xi. p. 166, and concluded.] 

 Vl/'E have received this year very important additions to the 

 * * knowledge of the alkaloids. What was formerly de- 

 scribed as Atropia, Hyoscyamia and Daturia must, according 

 to the discoveries of Brandes, be expunged. They are not 

 alkaloids; this discovery was left for Mein, Geiger and Hessef. 



* From Weigmann's Archivfur Naturgeschichtc, vol. ii., part iv., p. 139 

 et seq. Translated by Mr. Wm. Francis. 



f Geiger and Liebig's Anna/cn, vol. vii. p. 269. 



