SCIENTIFIC SUMMAET. 
425 
CHEMISTEY. 
The Hate at luhich chemical Actions take place. — Mr. Vernon Harconrt 
recently delivered a lecture before the Eoyal Institution, in which he dis- 
cussed this very important problem in Chemical Physics. The following 
propositions embrace the conclusions arrived at from the examination of 
cases of gradual chemical change ; — 1. The rate at which a chemical change 
proceeds is constant under constant conditions, and is independent of the 
time that has elapsed since the change commenced. 2. When any substance 
is undergoing a chemical change, of which no condition varies, excepting 
the diminution of the changing substance, the amount of change occurring 
at any moment is directly proportional to the quantity of the substance. 
3. When two or more substances act upon one another, the amount of 
action at any moment is directly proportional to the quantity of each of the 
substances, 4. When the rate of any chemical change is alfected by the 
presence of a substance which itself takes no part in the change, the accele- 
ration or retardation produced is directly proportional to the quantity of the 
substance. 5. The relation between the rate of a chemical chang-e occurring: 
in a solution, and the temperature of the solution, is such, that for every 
additional degree the number expressing the rate is to be multiplied by a 
constant quantity. 
The Detection of Nitroglycerine in cases of poisoning is a matter of some 
chemical interest. The method which has been recommended by Herr 
Werber is as follows : — The organic material to be tested is extracted with 
ether or chloroform, the extract mixed on a watch glass, with two or 
three drops of pure aniline, and evaporated upon the water-bath. A few 
drops of concentrated sulphuric acid are then added, when, if nitroglycerine 
is present, a purple coloration appears which changes to a dark green on 
dilution with water. As little as *001 grain of nitroglycerine may thus be 
identified. — Vide Zeitschr. Analyt. Chem., vii. 158. 
What is Iodide of Starch? — This question receives an answer in the recent 
enquiries of M. Guichard. M. Guichard thought that an examination with 
the dialyser would throw light upon the question. If there existed, in fact, 
a combination of iodine and starch, the compound ought to be colloidal, and 
remain in the dialyser ; if, on the contrary, only dissolved iodine and hydri- 
odic acid were there, starch would alone remain. M. Guichard made a great 
number of experiments, and he remarked that iodine passed the dialyser 
first, then hydriodic acid in large quantity, afterwards the iodide became 
suddenly decolorised, and later the iodine, as well as the hydriodic acid, 
ceased to be disengaged. When the experiment was made with iodide of 
starch decolorised by heat, the disengagement of iodine was difiacult to 
perceive, that of hydriodic acid was alone observed ; the same was the case 
with the iodide heated in close vessels for some hours to 100°, then to 150°. 
The colourless iodide of starch has then no existence ; the so-called iodide of 
starch is simply starch tinted by iodine. Heat thus separates the iodine 
from the starch ; the iodine then remains in the water, either as such or as 
hydriodic acid. 
How to bleach Palm Oil. — This is a practical point of considerable importance 
YOL. YII. — NO. XXIX. G G 
