58) NALTCORE 
[ NovEMBER 19, 1903 
lished the observation. The things necessary to produce it 
appear to be :—(r) a dry film of dust on surface of water ; 
(2) a layer of fine globules of moisture on the film; (3) a 
dead calm, that the globules be not shaken into coalescence ; 
(4) the sun shining brightly at a low angle through a clear 
atmosphere. Epwarp Hewitt. 
Municipal Museum, Vernon Park, Stockport, 
November 11. 
Weather Changes and the Appearance of Scum on 
Ponds. 
Ir the scum referred to (NATURE, November 5, p. 7) be 
organic in character—algal, for instance—it would contain 
bubbles of gases. 
Would not these bubbles tend to enlarge, from the ex- 
pansion of their contained gases, on a lowering of baro- 
metric pressure, and the mass, becoming specifically lighter, 
to rise? 
““Platanus orientalis’’ says ‘‘ any decided change of 
weather.’? The above explanation would hold good only 
for a change of weather indicated by a falling barometer. 
H. J. GLover. 
Stationers’ School, Hornsey, N., November 6. 
Earthquake at Kashmir. 
It may perhaps be of interest to note (I do not find the 
fact recorded in Nature) that on April 18, 1902, there was 
a sharp earthquake. shock over North-west India and 
Kashmir, about 2.30 a.m. (local time). 
O. ECKENSTEIN. 
34 Greencroft Gardens, London, N.W., November 13. 
A NEW THEORY OF THE “SOUL 
T has long been recognised that the chemical com- 
position of the soil affords a very imperfect index 
to its fertility, partly due to the fact that only recently 
have methods of analysis been devised to discriminate 
between the total plant food in the soil and that which 
is active and lilkely to be immediately available for the 
plant, but chiefly because the physical texture of the 
soil and its power of maintaining a supply of water 
to the growing plant is a much larger factor in crop 
production than its store of nutrient material. 
But though the part played by the chemistry of the 
soil has doubtless been much exaggerated and requires 
to be studied more in connection with soil physics, it 
has been reserved for the chemists of the United States 
Bureau of Soils to deny its action entirely, and put 
forward a theory which considers all soils to be 
effectively the same from the chemical standpoint. 
Briefly stated, the thesis developed in the Bulletin 
before us is as follows :—dissatisfied with the want of 
correspondence between the results of any of the 
methods of soil analysis in which the soil is attacked 
by either weak or strong acids, Dr. Whitney and his 
associates have fallen back on the aqueous solution 
obtained by shaking 100 grams of the soil with 
500 c.c. of water and allowing it to stand for twenty 
minutes. For the rapid quantitative examination of 
the very weak solution thus resulting they have worked 
out various colorimetric methods, and in this way have 
been able to analyse several hundred soils of the be- 
haviour of which in the field something was known. 
From these results the authors come to the con- 
clusion ‘ that with occasional exceptions the composi- 
tion of the soil solution and the concentration is about 
the same in all cultivable soils.’’ ‘ All our principal 
soil types, in fact, practically all cultivable soils, con- 
tain naturally a nutrient solution which varies within 
comparatively narrow limits with regard cither to 
composition or concentration, and which is usually 
1 “The Chemistry of the Soil as related to Crop Production.” 
Whitney and F. K, Cameron. 
Soils, No. 22. Pp. 71. 
By M. 
U.S. Department of Agriculture, Bureau of 
(Washington, 1903.) 
NO. 1777, VOL. 69] 
sufficient for plant growth. Apparently, therefore, all 
soils are amply supplied with the necessary mineral 
plant foods, and these plant foods are not in them- 
selves a matter of such paramount importance to the 
agriculturist, for their supply as regards the plant is 
determined by the supply of soil moisture which the 
crop can obtain from the soil.’ The authors further 
suggest that fertilisers, if they have any effect in in- 
creasing the crop, do so in the main by altering the 
physical texture of the soil or by stimulating the root 
range of the plant. So novel a point of view from men 
with the experience of Dr. Whitney and his colleagues. 
demands a careful consideration of the evidence in its 
support. 
On the theoretical side the authors suggest that in 
the natural soil solution on which plants feed ‘‘ the 
quantity of any constituent which can possibly enter 
the solution is . . . determined by definite equilibrium 
conditions with the but slightly soluble mineral from 
which it is derived . . . it may very well happen that 
the addition of comparatively small amounts of a 
readily soluble potassium salt to a soil would simply 
force back the dissociation and solubility of the potash 
minerals with no consequent gain of potassium to the 
soil solution.’? In support of this view the authors 
describe an experiment in which powdered potash 
felspar when shaken up with water is shown to yield . 
a feebly alkaline solution, as indicated by phenol- 
phthalein. On adding, however, a_ little .soluble 
potassium salt the colour of the phenolphthalein is 
partly discharged, which the authors consider to in- 
dicate that some of the potash derived from the felspar 
has been forced back to the solid phase. We would 
suggest the consideration of another experiment; take 
a very weak solution of potassium phosphate, add a 
drop of phenolphthalein solution, and run in dilute 
alkali until a distinct colour appears; now add a little 
solution of some neutral salt, sodium or potassium 
chloride; the colour will again be partially discharged, 
although the salt added is strictly neutral. 
In the latter experiment there is no question of the 
intervention of a solid phase; both experiments are, we _ 
think, equally explicable on the dissociation hypothesis, 
but the one does not bear the interpretation put on it 
by the American chemists. 
Turning now to the analytical figures, we canndt 
agree that, except in a very general and average sense, 
they support the authors’ case that the composition 
and concentration of the soil solution are about the 
same for all soils. Taking first of all the determin- 
ations of nitric acid, they are seen to vary within the 
widest limits, as is evident from the following 
summary of the results for four of the soils :— 
Nitric Be BLAS 
thik 5 : 
No. of per million of dry soi ee 
analyses ——— 
Highest Lowest 
Windsor Sand ; 34 26 62 | 0°56 5°69 
Norfolk Sand ee 98 23°76 0°67 381 
Leonardtown Loam 62 62°00 trace D270 
Sassafras Loam | 80 38°40 | 0°50 7°79 
Furthermore, if the number of the determinations 
falling within successive equal limits be plotted into 
a curve, the resulting figure is highly irregular, and _ 
shows nothing of the maximum about the mean which 
characterises the curve of error. The nitric acid 
figures are thus entirely opposed to the authors’ thesis ; 
they show no tendency to a constant value, but extreme 
accidental variations, i.e. due to factors independent 
of the classification here adopted. But in fact too 
