450 Proceedings of Royal Society of Edinburgh. [sess. 
formed by the outline of the cleavage face had an obtuse angle 
of about 135°. 
Until recently I was unable to continue the investigation, but, 
owing to the publication of a paper by Werner on “ The Behaviour 
of Chromic Hydroxide towards Oxalic Acid and certain other 
Organic Acids” (J. Chem. Soc., 1904, 85 , p. 1438), I have con- 
sidered it desirable to publish a preliminary note, although the 
results so far obtained can only be stated generally. 
Several preparations have been made similar to that described 
abov’e, and the crystalline products analysed for chromium. The 
percentage varies considerably in the different preparations, and as 
yet it is impossible to state what is the maximum, but specimens 
hitherto analysed show considerably less than 1 per cent. Since 
potassium hydrogen succinate crystallises in monoclinic crystals 
possessing a plane of symmetry and showing perfect cleavage 
faces parallel to it, the small amount and the fluctuation in that 
amount of chromium present in these crystals lead to the 
assumption that they are potassium hydrogen succinate, the 
external surfaces being modified by the presence of some chromium 
compound, possibly in solid solution. 
Attempts have also been made to dissolve other hydroxides and 
certain carbonates in potassium hydrogen succinate solution. 
When copper carbonate was taken a precipitate of copper 
succinate was first produced ; the filtrate from this was coloured 
slightly blue, and after standing for some time deposited crystals 
of the acid succinate. These showed six-sided prism faces, and 
also, superimposed on these, curved faces similar to those observed 
with chromic hydroxide. 
Crystals showing traces of these curved faces have been obtained 
from solutions in which aluminium hydroxide had been dissolved. 
Equal quantities of fairly concentrated solutions of potassium 
hydrogen succinate and ferric chloride (containing a few drops of 
hydrochloric acid) were mixed, and in a few minutes a brick-red 
precipitate appeared. The solution and precipitate were boiled 
with another equal quantity of potassium hydrogen succinate, the 
precipitate filtered off, and the filtrate, which was slightly yellow 
in colour, set aside to crystallise. At the end of three weeks pale 
yellow crystals were found at the bottom of the crystallising 
