TRANSACTIONS OF SECTION B. 445 
permanganate gave them a considerable power of resistance to the action of the 
water. 
Sheet Lead.—Many experiments were made on the sheet lead ‘ erosion’ test, 
and for practical purposes a duration of one day is preferred to the seven or 
fourteen days suggested by Dr. Houston. We find that erosion is due to the 
action of oxygen in the presence of water. The amount of lead eroded is 
affected by the distance from the lead to the water surface, is generally pro- 
portional to the area of the surface of the lead exposed, and does not depend 
on the volume of the water. 
With untreated water carbon dioxide up to one per cent. by volume pro- 
duced little effect on the amount of erosion; when two or more per cent. of 
carbon dioxide is present erosion no longer occurs, for the liquid remains clear, 
but Jead is dissolved, in amount much less than that removed by erosion. Given 
sufficient oxygen, the alkalinity of the water is the principal factor determining 
the amount of erosion. The use of (a) lime to prevent erosion was not found 
satisfactory, the presence of three to nine parts per 100,000 of water reduced 
the erosion, but smaller or larger quantities were of little, if any, use. Four 
parts per 100,000 of (b) calcium carbonate gave protection, and as little as two 
parts per 100,000 of (c) calcium bicarbonate were sufficient to practically prevent 
erosion. Filtration through sand had little effect on the action of the water 
on lead. No evidence was found of a seasonal variation in the action of the 
water on lead, though the colour and amount of organic matter varied 
considerably. 
TUESDAY, SEPTEMBER 16. 
Discussion on Radio-active Elements and the Periodic Law. 
(i) The Radio-Elements and ihe Periodic Law. 
By Freperick Soppy, M.A., F.R.S. 
During the present year, 1913, the general law governing the passage through 
the periodic table of the elements in process of radio-active change has been 
discovered. As the result it is possible to write the three disintegration series 
of uranium, thorium, and actinium across the periodic table, so that each mem- 
ber falls into its proper place in the case of the twenty-seven members the 
chemistry of which is known. For the six members the period of average life 
of which is too short for the chemical nature to be determinable, and for the 
five inactive end-products, the chemical nature can be without uncertainty pre- 
dicted. The general law is that in an a-ray change, when a helium atom carrying 
two atomic charges of positive electricity is expelled, the element changes its 
place in the periodic table in the direction of diminishing mass and diminishing 
group number by two places. In a f-ray change, when a single atomic charge of 
negative electricity is expelled from the atom as a f-particle, and also in the two 
changes for which the expulsion of rays has not yet been detected, the element 
changes its position in the table in the opposite direction by one place. 
The generalisation as regards the a-rays was put forward in 1911,' but at that 
time the chemistry of the B-rays giving members, which are mostly short-lived, 
was not known well enough for anything definite to be said. Fleck in 1911 com- 
menced to make a systematic investigation of the chemically indefinite members, 
from the point of view adopted in the book referred to, of the existence of 
chemically identical and non-separable groups of elements. This work occupied 
two years. Some of the results were communicated to this Section at the Dundee 
Meeting last year, and they have since been published in the ‘ Journal of the 
Chemical Society.’? It is important to note that this work was purely experi- 
mental, and was done deliberately without any attempt to find the theoretical 
law, in order that the results might be free from all bias in favour of any par. 
' Soddy, Chemistry of the Radio-Elements, p. 29. 
* Proc., 1913, 29, 7 and 172; T'rans., 1913, 103, 381, and 1052. 
