j 
Feb. 1, 1883] 
NATURE 325 
December, 1882), sets up two baro-manometers, one on the (low) 
ground, the other at the top of a high building, or of a hill. 
The manometric branches are connected by means of a long 
metallic tube. On rarefying the air in the tube through an 
adjutage adapted near one of the manometers, the rarefaction is 
prepagated towards the other, but owing to gravity, the lower 
one always shows a greater pressure than the other. By varying 
the conditions, the hypsometric formula may be established 
directly. To ascertain whether gases have or have not a limit 
of elasticity, two baro-manometers are placed below and con- 
nected by separate tubes with the one above. On rarefying 
through a tube near one of the lower manometers, a limit is 
reached at which gravity prevents the air of the latter manometer 
from rising, and it remains stationary while the other continues 
to fall, if the limit of elasticity exist. The author was fitting up 
his apparatus for these experiments on a very high old building 
at St. Petersburg. 
In another paper to the same Society (/oc. cit.), M. Piltschikoff 
describes an arrangement for measuring the refractive index of 
liquids of which one has but small quantities. A hollow lens is 
filled with the liquid, and with the aid of a graduated scale and 
a microscope, one measures exactly the focal distance of a mono- 
chromatic flame placed at a given distance from the lens. The 
author gives a simple formula for calculating the index of the 
liquid, when the constants of the apparatus have been determined 
once for all. In one set of experiments, the index of glycerine 
was found = 147298, with a probable error estimated at 
+ 0°00001. : 
In the common practice of referring the electromotive force of 
galvanic combinations to the Daniell element as unit, some diffi- 
culty and confusion have arisen from differences in the construc- 
tion of that element by different physicists. In a recent investi- 
gation of this matter (Wed. Ann., 13, 1882), Herr Kittler 
gives the name of ‘‘normal element” to a combination, which 
is as follows :—Amalgamated, chemically pure zinc, in dilute 
sulphuric acid of specific gravity 1°075 at 18° C. ; and chemically 
pure copper in concentrated copper sulphate solution of specific 
gravity I°190 to 1°2c0__ He finds that the electromotive force of 
the Daniell element (Zn, H,SO,, CuSQO,, Cu) increases with 
percentage proportion of the acid to a maximum occurring at 
the same place, whether the copper sulphate solution be concen- 
trated or dilute, viz. with 25 to 30 per cent. of the acid ; with 
further hydration of the acid there is decrease. The increase is 
greater, ho ever, the more dilute the CuSO, solution used, and 
greatest with pure water. It is further found that, if very weak 
acids are used, there is decrease of the electromotive force with 
dilution of the copper-sulphate solution. Accordingly, there is 
a degree of concentration of the acid, with which a Daniell 
element furnishes the same tension, whether the CuSO, be con- 
centrated or diluted to any extent. The solution in question has 
the specific gravity I‘oorr at 16° C., and is compounded of 
750 ccm. H,O and 100 cem. dilute H,SO, of sp. gr. 1007. 
Herr Kittler compares the action of his ‘* normal element” with 
that of other practical units. 
IN a recent paper to the Vienna Academy (Wed. Ann., 13, 
1852), Prof. Stephan describes an investigation of the maguetic 
Screening action (Schirmwirkung) of iron (which is exemplified 
in Thomson’s marine galvanometer and the Gramme machine). 
His experiments were made with hollow iron cylinders and iron 
rings, and were of three kinds, viz. deflection, oscillation, and 
induction. 
‘THE sound-vibrations of solid bodies (glass cylinders) in contact 
with liquids has been lately studied by Herr Auerbach (/Vied. 
Ann., No. 13, 1882). He finds that the geometrical lowering of 
Zone, represented by the ratio of the vibration number (7) of the 
empty vessel to that of the same vessel filled with water (7), is 
smaller the higher the tone of the empty vessel, aid greater the 
narrower the vessel. The arithmetical lowering of tone (repre- 
sented by (7) —7)7z)) in a ves-el of mean pitch, is inversely pro- 
portional to the square root of the vibration-number of the empty 
glass, and (approximately) to that of the number of wave-lengths 
which the sound of the empty vessel traverses from the wall to 
the axis, In glasses of different width it is (approximately) 
inversely proportional to the square root of the width. ‘lhe 
specific lowering of tone of a liquid depends primarily on the 
density, and is greater, the greater this is, though it does not 
increase so quickly ; next, on the compressibility, being greater 
the smaller this is. 
AN INQUIRY INTO THE DEGREE OF SOLU- 
BILITY REQUISITE IN MANURES, WITH 
SPECIAL REFERENCE TO PRECIPITATED 
CALCIC AND MAGNESIC PHOSPHATES 
OME remarkable field trials, recently conducted in Scotiand 
by Jamieson and others, have tended to raise serious doubts 
coacerning the correctness of the high relative values, hitherto 
| assigned by chemists to dissolved phosphates, commonly termed 
super-phosphates, for manurial purposes. We propose, there- 
fore, to examine briefly the action of phosphates in the soil; the 
conditions under which they become available for the nutrition 
of plants, and the degree of solubility which, considering these 
facts, would appear to be most adva tageous fot the purposes of 
the agriculturist. We hope to be able to show the great value 
of precipitated calcic and magnesic phosphates as manure- 
ingredients, and to assign some reasons for the comparative 
neglect which the salts of magnesia have hitherto received from 
agricultural chemists. 
The careful and elaborate series of experiments undertaken by 
Dr. Voelcker respecting the ‘‘solubility of phosphatic mate- 
rials” may be said to constitute the basis of our present inquiry, 
as the behaviour of phosphates in water is perhaps the readiest 
test of their activity as manures. Dr. Voelcker ascertained that 
one gallon of distilled water will di solve the following amount 
of calcic pho-phates, derived from the sources quoted :— 
Per gallon. 
Estremadura phosphorite... o'IO grains. 
iWorwepian apatites 225 so eee) een eae ee) OA; 
Coprolites (mean of Suffolk and Cambridge- 
SHIE)|. jeder) decors O:62 ass 
Monk’s Island phosphate ... ... ... «. LOO ,, 
Pure bone ash (from very hard bone) ... ... 118 ,, 
Pure tribasic phosphate of lime, precipitated, 
burnt and finely ground passe Boel Es 
Guano occt Spee ae one enone” (osc Ce OSs s 
Pure tribasic phosphate, precipitated and 
still moist beats SESOn iiss 
The general deductions arrived at from these experiments, 
made about fifteen years ago, were that the phosphates in 
coprolites, apatite, and other phosphatic minerals were very little 
acted upon by water, and that ‘‘ for agricultural purposes phos- 
phatic minerals, as well as bone ash, should be treated with a 
quantity of sulphuric acid sufficient to convert the whole of the 
insoluble phosphates, therein contained, as completely as possible 
into solnble combinations. It is a waste of good raw materials 
to leave much of the insoluble phosphates unacted upon by 
acid.” Broadly speaking, the above may be said to constitute 
the creed of the agricultural chemist at the present day, and the 
farmer buys his manure at a relatively high price, per unit of 
soluble phosphate. 
On ap lying manures containing dissolved phosphates to tne 
soil, nearly the whole of the phosphoric acid is at once neut- 
ralised by the various salts present therein, be they lime, 
alumina, or iron, and the chemist assures us that the superior 
estimation in which soluble salts are held arises from the 
property possessed by these salts of becoming rapidly diffused 
through the soil and precipitated therein, in an extremely fine 
state of sub-division. Voelcker, in some recent obs:rvations on 
this question, lays down certain propositions which are thus set 
forth in the abstract of the Yournal of the Chemical Society, 
vol. xi. (1881) p. 640. These appear to us to state very clearly 
and briefly the accepted theories respecting the action of phos- 
phates in manure. 
I. Phosphetes are not readily taken up by plants in a soluble 
form, but must be returned to an insoluble cond tion before they 
yield their useful properties. 
2. The efficacy of insoluble calcium phosphate corresponds 
with the minuteness of division in which it is found in a 
manure, 
3. The finer the particles in a phosphatic material, the easier 
it is dissolved in water, and the more energetic its action as a 
manure. Coarsely-ground coprolites and other minerals are less 
useful than the same materials in fine powder. 
4. Calcium phosphate in porous soft bones is more soluble 
and energetic than in hard bones, and is more available in bone 
meal than in crushed bones. 
5. Calcium phosphate in crystallised mineral phosphates— 
Norwegian, Canadian, and Spanish apatites, for example—is less 
