142 Prof. Liveing, On photographing a Spectrum. [April 27, 



refrangible rays were somewhat diverted downwards, and the image 

 of the slit produced by them fell on the film at a different level 

 from that produced by less refrangible rays. Consequently the 

 spectrum of the second order in the photograph was about half 

 the length of the lines lower than the part of the spectrum of 

 the first order at the same place, and the two orders were at once 

 distinguished. 



It is not at all difficult with a table of sines to set out a scale 

 of wave-lengths for a spectrum formed in this way, and such a 

 scale once made would of course apply to all photographs taken 

 with the same instrument, provided there were no inequalities in 

 the shrinking of the films when drying after development. Un- 

 fortunately Professor Liveing had found that the films, inelastic 

 as they seem even when wet, did not shrink uniformly, and he 

 was therefore turning his attention to glass plates. Glass plates 

 will not bend to cylinders of so short a radius as o\ feet without 

 danger of fracture, but thin sheet glass can easily be bent to a 

 cylinder of double that radius. He was therefore fitting up a 

 suitable camera for use with a large grating of 21 feet radius, 

 and hoped to obtain photographs with it which should not only 

 be useful for reference, but from which wave-lengths could be 

 read off to a close approximation. At present he could only read 

 off wave-lengths from the films by photographing a known spec- 

 trum, such as that of iron, at the same time and on the same 

 film as the other spectrum, and measuring the distance of the 

 unknown line from the nearest lines of known wave-length, a 

 much more troublesome process than the simple application of a 

 scale. 



(2) On dioxymaleic acid and its derivatives. By H. J. H. 

 Fenton, M.A., Christ's College. 



By oxidation of tartaric acid, in presence of a ferrous salt, a 

 substance results which has powerful reducing properties, and 

 which gives a beautiful violet colour with ferric chloride. This 

 substance has been isolated and proves to be an acid having the 

 formula C 4 H 4 6 . It crystallizes with 2H 2 in flat diamond-shaped 

 plates, having a pearly lustre. The isolation of the acid was a 

 matter of extreme difficulty owing to the unstable nature of its 

 aqueous solution, which decomposes slowly at ordinary tempera- 

 tures, and very rapidly when heated, giving glycollic aldehyde 

 and carbon dioxide. Glycollic aldehyde has, in this way, been 

 isolated as a syrupy liquid ; when heated to 100° in a vacuum it 

 undergoes polymerization, a sweet-tasting solid gum being pro- 

 duced which has the formula C 6 H 12 6 . 



