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We 
Sept. 23, 1886] 
from the sanitary officers, and visited bed-rooms and similar 
places during all parts of the day or night, while aciually occu- 
pied by the inhabitants. Houses are divided in the tables into 
one-, two-, and four-roomed dwellings, and mention was made 
of some cases in single-roomed dwellings in which eight persons 
‘were found sleeping in a single bed, and in many cases no bed 
was found in the dwelling at all, The impurities in the air of 
such houses were naturally much greater than in better class, 
and by a careful comparison of chemical composition of the air 
with the death-rates from various causes in the various classes of 
houses, it was shown that on an average the length of life in a 
one-roomed house was only twenty years, whilst that in better- 
class houses is forty years. Hence a person born and living in 
a one-roomed house has a chance of living only half as long as 
those born and living in a four-roomed house. This depends 
naturally to a considerable extent on other causes than impure 
air-supply. Some irregularity was observed in the cases of 
consumy tion, scarlet fever, and diphtheria, which is, however, 
quite capable of explanation. The influence of cubic space on 
the purity of the air in dwelling-rooms was somewhat un- 
expected, the best results being noticed when 1000 cubic feet 
was allowed for each person. With larger rooms, owing to 
stagnation of the air, the result is not so good. Sixty-eight 
schools in Dundee were examined ; of these, twenty-six were 
mechanically ventilated, while the others were ventilated by 
means of windows. The advantages were distinctly in favour of 
mechanical ventilation, the micro-organisms being one-seventh, 
and the carbon dioxide one-half of that in the other schools. 
Mechanical ventilation not only materially improves the quality 
of the air, but also has less influence in unduly reducing its tem- 
perature. On comparing together Loys’ and girls’ schools the 
air is almost invariably less pure in boys’ schools. The amount 
of carbon dioxide does not afford any indication of the amount 
of organic matter or micro-organisms, except by taking the mean 
of a large number of experiments. Cleanliness of person has a 
comparatively small influence on the number of micro-organisms, 
but cleanliness of dwelling-rooms and schools has a most im- 
portant effect. Hence the air of new schools is distinctly better 
than that of older buildings. In conclusion, the author suggested 
that in many cases the evil said to be due to over-pressure in 
schools was doubtless due to imperfect ventilation, and that if 
Dundee may be fairly regarded as an example of a British town, 
then certainly our schools are most imperfectly ventilated ; and 
that for improvement in this respect the advantage of mechan- 
ical ventilation should be strongly insisted upon. 
The Preservation of Gases over Mercury, by H. B. Dixon, 
M.A., F.R.S.—From a statement in Bence-Jones’s ‘ Life of 
Faraday ” it would appear that a difference of opinion between 
Faraday and Davy existed on this point, and according to the 
experiments of the former gases cannot be indefinitely preserved 
over mercury, whilst the latter found that hydrogen could be 
preserved over mercury for a considerable time without suffering 
change. The author has examined various gases, including 
hydrogen, cyanogen, sulphur dioxide, and electrolytic gas, which 
had been kept over mercury for periods ranging fro. 25 to 94 
years, and concludes that the gases had suffered no change in 
the time. 
The Dist: ibution cf the Nitrifying Organism in the Svil, by 
R. Warington, F.R.S.— Previous experiments have shown the 
limit of depth at which this organism exists in soil to be about 
18 inches, but later experiments have shown it to exist at depths 
of 3 feet, and in some cases at depths of 5 and 6 feet. 
The Fading of Water Colours, by Prof. W. N. Hartley, 
_F.R.S.—The author, referring to the correspondence in the 
Times and to an article in the Wéveteenth Century on this 
subject, pointed out that two ideas had been brought forward 
in connection with this matter—one being that water-colour 
drawings fade on keeping, while others have contended that the 
tints increase in depth on keeping for a length of time. Hence, 
on the one hand it has been recommended to keep water-colour 
drawings in the light, while others have suggested that darkness 
is preferable. Colours used are of two kinds, mineral and 
organic. Mineral colours are generally unalterable, except in 
_ special colours, such as lead. The tendency is for red light to 
“act as an oxidising agent on such colours, while violet light 
exerts a reducing action. But in the case of organic colouring- 
_ matters oxidation is promoted by light from either end of the 
spectrum. Acidity in any form is a great cause of the deteriora- 
~ tion in water-colours. The chief sources of acidity are the im- 
" purities in the atmosphere in presence of moisture, imperfectly 
nl 
NATURE 
511 
prepared colours, and the acidity of the paper. The paper is 
always itself slightly acid, and the ue of size or gum is a 
source of acidity, while the burning of coal and of gas in towns 
produces a sensible amount of sulphurous acid in the atmosphere. 
The author has carefully examined the effect of acids, of ex- 
posure to sunlight, of hydrogen peroxide, and of sulphurous acid 
in the case of sixteen common water-colours. As a result he con- 
cludes that the character of the colours examined is very creditable 
to the manufacturer. Lakes are very permanent in pure air; 
while cases are known where indigo has remained unchanged 
for upwards of 1800 years. Indigo is, however, liable to be 
attacked by acids. Generally the effect of chemical agents upon 
water-colours is what might have been expected from their 
chemical composition. Thus yellows containing cadmium sul- 
phide are bleached by oxidising agents. In some few cases, 
however, unexpected results were obtained. Ultramarine is 
very readily affected by dilute acids; 10 preparation of lead 
should be used as a pigment either for oil or water-colour 
drawing. It is shown that many water-colour drawings have 
been exposed to light for fifty years or more in properly arranged 
galleries, without appreciable deterioration. The tendency is 
to produce apparently darker tints, owing to the lighter tints 
being most likely to fade, while the brown colour developed 
in the paper itself tends to produce a similar effect. To pre- 
serve delicate sunlight effects the drawings should be kept in 
rooms imperfectly illuminated, and preferably with blinds trans- 
mitting a yellow or brown light. They should be carefully 
protected from the effects of an impure atmosphere, while paste 
or gum should not be used in affixing them. A slight wash of 
borax on the paper destroys its acid reaction, and makes the 
colours fix readily on the fibres. A small quantity of borax 
might be used in the water employed for mixing the colours. 
For illuminating galleries incandescent lamps are to be pre- 
ferred to lighting by the electric arc, as the latter may be 
regarded as a sure means of destruction of the colours. 
The Colour of the Oxides of Certum and its Atomic Weight, 
by H. Robinson, M.A.—A criticism of the work of Wolf, on 
the atomic weight of cerium, published in the American Fournal 
of Science and Art, 1868, upon which the atomic weight, 138 
cerium, given in Clark’s ‘‘ Constants of Nature,” is based. The 
author contends that Wolf’s method of preparation would give 
lanthanum and not ceric oxide; experimental evidence was 
given in support of this contention ; further the author maintains 
that ceric oxide is yellow and not white, as described by Wolf. 
Cn the Relative Stability of the Hydrochloride C\)ff,,Cl Pre- 
pared trom Turpentine and Camphene respectively, by E. F. 
Ehrhardt (Mason College).—According to Ribau the first of 
these hydrocklorides is the less easily decomposed by water, 
whereas the author finds it to be the one most easily decomposed 
under the influence of temperature. Ata low red heat Tilden 
has shown turpentine is more completely dissociated than cam- 
phene, and this the author has shown to be true for lower tem- 
peratures. The paradoxical result that the hydrochloride of the 
moe stable hydrocarbon is less stable than that from the unstable 
one, is regarded as proving this compound to be a molecular one, 
in which the chlorine is associated with the hydrogen of the acid 
and at the same time to the hydrocarbon. Bs 
On Derivatives of Tolidine and Azotolidine Dyes, by R. F. 
Ruttan, B. A., M.D.—An account of the preparation of tolidine, 
which is the homologue of benzodine, and obtained by a similar 
mode of preparation. Several derivatives of this base wer 
described, as also azotolidine or tetra-azoditolyl, which is pro- 
duced by the action of nitrous acid on the base. This compound 
forms the starting-point in the preparation of a series of important 
dyes, by which cotton and wool fibre may be dyed without the 
use of a mordant. re 
On the Chemistry of Estuary Water, by H. R. Mill, D.Sc. 
—The salinity (ratio of total dissolved matter in water) has been 
determined from point to point in the Firth of Clyde and Firth 
of Forth. In the case of the latter the distribution of salinity 
has been shown to be constant all the year round, whilst in the 
‘case of the Clyde there are periodical variations through the 
whole mass of the water. In the case of the Forth River 
entrance, it is evident a mixture of river and sea water takes - 
place by a true process of diffusion, maintaining a constant gra- 
dient from river to sea. The dissolved matter of fresher water 
was found richer in calcium carbonate than sea water. 
The Essential Oils; a Study in Optical Chemistry, by Dr. 
Gladstone, F.R.S.—After explaining how the refractive equiva- 
lent of an organic compound may be used to determine its con- 
