THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
87 
. August 3,1872.] 
Viewed in another aspect, triad indium occupies a 
position intermediate between the positions of its remote 
triad congeners, aluminium and thallium. The mean 
atomic weight of the three metals being 114 - 3, the atomic 
weight of indium is 113‘5. The mean specific gravity 
of the three metals being 7*3, the specific gravity of 
indium is 7'4. And in respect of purely chemical habi¬ 
tudes, hydrated alumina and hydrated. india might 
easily he mistaken for one another. It is interesting, 
moreover to remark that the last-discovered two metals 
indium and thallium—discovered, it will he remembered, 
hy the same process, that of spectrum analysis—should 
hear to one another much the same sort of relation that 
is borne to one another hy the jovian and saturnine 
"metals of the alchemical or even pre-alchemical era. 
Just, for example, as the unstable and least-known 
■chloride of lead, Pb Cl 4 , corresponds to the stable chloride 
of tin, Sn Cl 4 , so does the unstable and least-known 
chloride of thallium, T1 Cl 3 , correspond. to the stable, 
■and as yet only known, chloride of indium, In Cl 3 , as 
suggested, indeed, by the lecturer some six or seven 
years ago. 
The study of such relationships necessarily suggests 
many inquiries. Arranging the entire fifty-eight ele¬ 
ments of which the atomic weights are known, in a table 
•similar to the preceding one for the forty-six elements 
having atomic weights not exceeding 137, some twenty 
or five-and-twentv new elements would be required 
to fill up the gaps “in the different series; but why should 
not new elements be discovered having atomic weights 
as much above that of uranium, 240, as its atomic 
weight is above that of barium, 137 ? 
Again, does it seem probable that bodies capable of 
being arranged in such a well-marked numerical series, 
are really elementary and mutually independent; or is it 
more likely that the gradation of properties and atomic 
numbers manifested by these bodies, depends on their 
possession of different increments of common material P 
May it not be that the numerical ratio between the 
X 
atomic numbers of proximate elements, — = approxi- 
y y . 
matively—, is really absolute ; and that it will hereafter 
/be proved to be so by a better determination of atomic 
weights. Seeing that a short time back, caesium with 
"the atomic weight 133, and rubidium with the atomic 
weight 85, both occurred as unrecognized impurities 
in potassium with its atomic weight, 39, who shall 
answer for the absolute accuracy of even the best 
■established of our present atomic weights P . 
Again, the mean difference in atomic weight between 
•consecutive analogous elements, is, in the case of. the 
nine following pairs of elements, lithium and sodium, 
glucinum and magnesium, boron and aluminum, carbon 
and silicon, nitrogen and phosphorus, oxygen and sul¬ 
phur, fluorine and chlorine, sodium and potassium, mag- 
mesium and calcium, 16T ; the lowest difference being 
15, and the highest 17. The mean difference in the 
case of the four following similar pairs of proximate 
elements, phosphorus and vanadium, sulphur and 
chromium, chlorine and manganese, arsenic and nio¬ 
bium, is 19.25 ; the lowest difference being 19, and the 
highest 20-5. Lastly, the mean difference in the case 
•of the seven following similar pairs of proximate ele¬ 
ments, calcium and zinc, vanadium and arsenic, man¬ 
ganese and bromine, rubidium and silver, strontium and 
■cadmium, silver and caesium, tantalum and bismuth, is 
.24-6; the lowest and highest differences, even in the 
case of these elements of such high atomic weight, being 
23 and 26 respectively. Are these differences in atomic 
weight only approximatively, or are they indeed abso¬ 
lutely, 16, 20 and 24 respectively; and if so,. why 
.should the numerical difference between proximate 
.associated elements be 16 in one set of cases, 20 in 
in another set, and 24 in a third ? 
TURBIDITY OF LONDON WATER. 
In a Report to the City Commissioners of Sewers for 
the year 1871, Dr. Letheby makes the following remarks 
on the alleged turbidity of the London water-supply : 
“ The water supplied to the City by the New River 
and East London Companies has been invariably bright 
and nearly colourless; and so also has been that of the 
Kent and West Middlesex Companies ; but that of the 
Southwark and Vauxhall Company has been turbid on 
one occasion, that of the Lambeth Company on five 
occasions, and that of the Chelsea and of the Grand 
Junction Companies on eight occasions respectively. 
The turbidity has been at ail times due to the presence 
of a very small quantity of finely-divided clay, in which 
there was occasionally a trace of vegetable tissue ; and 
no doubt it had been caused by the heavy floods of the 
river. Although perfectly harmless, a slight turbidity 
of the water is sure to command attention, and may 
easily be made the subject of popular clamour.” 
The Lancet in publishing these remarks comments on 
them as follows : 
These statements are so positive, in some respects so 
improbable, and in all so different from those published 
by the Registrar-General on the authority of Dr. Frank- 
land, that we are compelled to examine them somewhat 
critically. And we must confess that the more we 
examine them the more unsatisfactory do they appear to 
us. On the mere question whether the waters are clear 
or turbid, for example, we often find the reports of 
householders in direct opposition to that of Dr. Letheby. 
A lady who lives at Wandsworth complained to us the 
other day that the water supplied to her was never quite 
clear, and was often “muddy.” She is compelled to 
refilter every drop used in the house, and asserts that 
the members of her household know the difference in 
taste as well as in appearance between the filtered and 
unfiltered water. A tumbler of each was brought to us ; 
we saw the difference at a glance, although the weather 
was dry, and the water in consequence better than 
usual. How is this to be reconciled with Dr. Letheby s 
statement, that in 1871 the water of the Southwark 
and Vauxhall Company was turbid “ on one occasion. 
Again, with regard to the quality of the turbidity. 
How can Dr. Letheby prove that ot all the foul impuri¬ 
ties w T hich mix with the sources of our water-supply only 
“ clay and vegetable tissue ” are able to pass through 
the filters ? We all know the difficulty of separating 
clay from water by filtration, but surely the very fact 
suggests the idea that other matters, more noxious and 
less easy of recognition, may be equally difficult to 
remove. And here, again, the idea is confirmed at once 
by common observation and by experiment. Our Wands¬ 
worth friend informed us that three times in the last 
few years the water-pipes of her house, had been choked 
up with large eels ; and stories of this kind are pretty 
rife. Does Dr. Letheby reckon an eel as clay or as 
vegetable tissue F The evidence of experiment is even 
stronger. Dr. Frankland found that water contami¬ 
nated with one-five-hundredth of the rice-water discharge 
of cholera remained opalescent after filtration through 
| paper, or even animal charcoal, both much better filter¬ 
ing materials than the sand used by water companies. 
• That sand should be capable of removing organized 
germs—spores, ova, or corpuscules—- from water which 
contained them is indeed a notion so improbable as to be 
almost absurd. Dr. Letheby would seem to concede as 
much; for he quotes with approval the remarks ot 
Major Bolton, that “ it is impossible altogether to get 
rid of the simplest forms of vegetable life by the most 
perfect filtration.” 
! The case, divested of all exaggeration, appears to 
stand thus :—It is highly probable, that imminent usk 
1 attends upon the use of water which contains m sus¬ 
pension certain low forms of life, though it is conceded 
that other forms of life arc harmless. It is a fact that 
noxious and probably organized matters are introduced 
