50 Mr. C. J. Burnett on several Forms of Actinometer. 

 ture of undecomposed tartaric acid. The change is thus ex- 



C 8 H 6 12 + 4HI = C 8 H 6 8 +4HO+4I. 



Tartaric acid. Hydriodic Succinic 

 acid. acid. 



Dessaignes, in a letter* to the Secretary of the Academie des 

 Sciences, announces that he has effected the transformation of 

 tartaric acid into succinic acid by treating the former acid with 

 iodide of phosphorus. Dessaignes' view of the relations of these 

 acids does not differ from those of Kolbe. The paper in which f 

 the latter chemist developed his views, and in which he announced 

 that Schmidt was occupied with the above experiments, appears 

 to have been unknown to Dessaignes. 



These experiments of Schmidt and of Dessaignes acquire an 

 additional interest at the present time, when Perkins and DuppaJ, 

 by an experiment the reverse of that of Schmidt, have converted 

 succinic acid into tartaric acid. This has been done by means 

 of bibromosuccinic acid. When the silver salt of this acid is 

 boiled with water, it decomposes, forming bromide of silver and 

 tartaric acid. Thus : 



C 8 H 2 Br 2 Ag 2 8 +4HO = C 8 H 6 12 + 2AgBr. 



Bibromosuccinate Tartaric Bromide 



of silver. acid. of silver. 



The reaction is thus exactly analogous to that by which chlor- 

 acetic acid is converted into glycolic acid. 



V. On several Forms of Actinometer. By C. J. Burnett, Esq.§ 



[With a Plate.! 



To the Editors of the Philosophical Magazine and Journal. 



21 Ainslie Place, Edinburgh, 

 Gentlemen, April 13, 1860. 



APROPOS of the description of a "new actinometer" by 

 Dr. Woods, which, as I find in its republication in the 

 Photographic Journal of January 16, appeared first in your 

 Magazine, I would call your attention to an old actinometer of 

 mine, a rough sketch of which appeared in the Liverpool Photo- 

 graphic Journal of December 15, 1858. Without any insinuation 



* Comptes Rendus, April 1860. 



t Liebig's Annalen, March 1860. 



X Chemical Society, April 19. 



§ Communicated by Sir D. Brewster, K.H., F.R.S. &c. 



