SCIENTIFIC SUMMARY. 
317 
movement of this plant. They are quite spontaneous and depend upon 
no common stimulus. The phenomenon displays itself at all periods of the 
day and night, and there are often weeks of repose. The leaves, large and 
small, seem to share in the motion, which is described as a sort of trembling. 
Vide Coniptes Rendus , April 22. 
CHEMISTRY. 
Determination of Organic Impurities in Water. — Mr. Miles Smith has 
written a letter to our contemporary The Laboratory, in which he states that 
the investigations of Professor Wanklyn and Mr. Chapman have shown that 
the ordinary mode of determining organic matters by evaporation is erro- 
neous. If this be so it is a most important discovery, and it shows us how 
unreliable must be the results of the analyses, so often published, of our metro- 
politan waters. Professor Wanklyn has called attention to the fact that 
the organic matters present in natural waters are liable to undergo de- 
composition during evaporation, and that consequently the organic con- 
stituents found in the dry residue left by a water are not to be taken as 
a just representation of the organic impurities originally present in the 
water. The nitrogenous organic impurities of waters are especially liable 
to change, and if the evaporation be made in the presence of a powerful 
alkali evolve their nitrogen in the form of ammonia. Wanklyn and Chapman 
propose to detect and estimate the nitrogenous bodies in waters by taking 
advantage of this reaction. In point of fact, they propose to make a kind 
of Will and Varrentrapp’s analysis at moderate temperatures. The following 
experiments illustrate the qualitative application of the method. Arti- 
ficial waters were made by taking distilled water and putting into it small 
quantities of well-known nitrogenised organic matters, and the artificial 
waters were then examined. Eirst, however, it was shown that neither 
nitrates nor nitrites give ammonia when boiled with alkalies, and sugar. 
To half a litre of distilled water were added some sugar, baryta water, and 
a nitrate, the whole being then boiled down rapidly in a retort very nearly 
to dryness. No ammonia was evolved. The presence of ammonia in these 
experiments was ascertained by means of Nessler’s test, which is well known 
to be extraordinarily delicate. Nitrites treated similarly gave no ammonia. 
It was also shown that if a small quantity of an ammoniacal salt be taken 
and treated as above described, all the ammonia is evolved at the beginning 
of the evaporation, and towards the latter part of the distillation the dis- 
tillate comes over perfectly free from ammonia. 
Chemical Examiners to the London University. — Professor Williamson, 
Ph.JD., F.R.S., and H. Debus, Esq., Ph.D., E.R.S., have been re-elected 
Examiners in Chemistry for the University of London. The salary of each 
office is 175?. per annum. 
Illuminating Power of the Gas of various Cities. — In the lectures which 
Professor Frankland lately delivered at the Royal Institution, some very 
useful comparisons were made showing the relative illumination-values of 
the gas of different localities. Professor Frankland had the illuminating 
