530 REPORT—1904. 
by dissolving ordinary barium chloride crystals in a sample of the same water, 
and the two solutions were tested in two similar actinometers. The difference 
in the induction periods was so marked as to leave no doubt that soluble solids 
cau be rendered active. 
Preliminary experiments on the rate of decay of activity have shown that 
aqueous solutions retain their activity for a considerable period of time even when 
a current of air is passed through them. Barium chloride crystals, however, rapidly 
become inactive when they are exposed to the air for a few hours. It has also 
been observed that exposure of barium chloride to the action of radium rays does 
not render the salt active towards chlerine. 
Besides establishing the above facts, the work, as mentioned above, includes 
comparative measurements of the induction period and of the sensitiveness of 
mixtures of hydrogen and chlorine, which appear to throw doubt on theories 
based on the assumption of the preliminary formation of additive compounds, 
which are formed and decomposed in conformity with the law of mass action. 
The relation of the above facts to cloud formation has also been studied, but 
we have been unable to obtain any evidence of the formation of any intermediate 
substances in this way. 
It has been incidentally observed that the presence of air does not prolong the 
induction period, although the sensitiveness of the mixture is thereby enormously 
reduced, 
6. Exhibition of Effects produced by precipitating Silver Chromate in 
Gelatine. By Professor I. TRAUBE. 
7. Exhibition of Photographs of Sections of an Australian Siderite, 
By Professor A. Liversipae, /.R.S. 
8. Ueber Isocystein (Isothioserin). By Professor 8. GABRIEL. 
9. Saponarin, a Glucoside coloured Blue by Iodine. By G. Barcer. 
The substance known to botanists as ‘ soluble starch’ and occurring in the leaf 
epidermis of a number of plants has been isolated from Saponaria officinalis at 
the suggestion of Professor L. Errera, of Brussels; it is a glucoside, and has been 
named saponarin. The substance is obtained pure in the shape of minute needles 
by a special method of crystallisation from mixtures of pyridine and water, 
Saponarin is insoluble in water and all ordinary organic solvents, but readily soluble 
in dilute alkalies and in pyridine; it melts at 231° with decomposition. The 
solution in alkalies is intensely yellow, and when acidified the substance remains for 
a long time in a state of pseudo-solution ; in this condition it gives an intense blue 
or violet coloration with iodine dissolved in potassium iodide solution. 
The air-dried crystals of saponarin lose water when heated or when left in 
vacuo over sulphuric acid, The dried substance is extremely hygroscopic, and, if 
left in the balance case for au hour or so, takes up quantitatively the water it had 
previously given off. For combustion it was dried in vacuo till of constant 
weight, and the boat containing it was then placed in a stoppered weighing tube. 
The mean of five analyses of the substance dried in this way gave 
C = 5375 %.H = 516 % 
For the molecular weight determination pyridine was the only available solvent. 
The microscopic method was the most convenient, and gave the following result: 
A. solution of +299 gram in 2:96 grams of pyridine was isotonic with a 
benzil solution of :23 mole. Hence M = 436. 
