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Nov. 25, 1869 | 
NATURE 
109 
necessaries of life. It is satisfactory to know that the 
representations of the Italian doctor in the Honolulu news- 
paper procured for these outcasts some amelioration of 
their lot, although it. procured for himself abuse and ill- 
will. Asa frontispiece to the volume there is a woodcut, 
reproduced from a photograph, of the author surrounded 
by some of the lepers of Molokai. Other woodcuts are 
likewise given; but they are chiefly, if not solely, remark- 
able for their very primitive and inartistic character. 
Chemical Lessons.—Zecons de Chimie. Deuxieme edition. 
Par M. Alfred Riche. (Paris: Didot Freres, 1869.) 
LIKE almost all French treatises on elementary science, 
M. Riche’s book is clearly and concisely written, and the 
illustrations are perfect ; but although introducing many 
of the newest discoveries in the science (perhaps some- 
what too pointedly alluded to in the preface), M. Riche 
does not adopt the important new views lying at the basis 
of modern chemistry. He still adheres to the old equiva- 
lent notation, and therefore refuses to admit the cogency 
of the proofs which have carried conviction to the minds 
of almost all other chemists. The short historical intro- 
ductions under Combustion, the Atmosphere, Dissociation, 
and the Atomic Theory are of interest to the student 
especially an extract (p. 704) from a paper by Dumas on 
the history of chemical affinity since the time of Bayck- 
hausen, read before the Academy of Sciences last year. 
1SRyl clei Se 
NOLES ON STAEACTITES 
HE mineralogist is acquainted with few objects of 
greater beauty than the stalactitic forms assumed by 
many minerals. So curious are these natural growths, that 
I venture to offer a few remarks upon their artificial pro- 
duction. 
The dependent clusters which line limestone caverns 
are formed, as has often been explained, by the following 
process:—When water containing carbonate of lime oozes 
through a porous rock, each drop loses water and car- 
bonic acid by evaporation. As water saturated with car- 
bonic acid only retains o'r per cent. of carbonate of lime 
in solution, it follows that when the evaporation is con- 
tinued beyond the point of saturation, carbonate of lime 
will be deposited. Globules of water on the roofs of 
limestone caverns are always covered with a thin film: 
this gradually thickens, and a tube is formed. This tube 
increases in size mainly by the deposition of carbonate of 
lime from water running over its surface. There are, 
however, many cavities containing tubes of arragonite 
in an horizontal position, and even of a curved form. 
Mr. Wallace has shown* that the growth of such stalactites 
has been from within outwards, the solution travelling 
along the self-constructed tube. 
The following experiment affords a ready method of 
studying the somewhat rapid growth of similar forms:— 
Select a flat piece of porous sandstone, or, better, a slice 
of coke; saturate this with nitric acid. If a globule of 
mercury three or four millimetres in diameter be allowed 
to fall on the coke, the surface of the mass will be covered 
with minute beads of mercury. The nitric acid imme- 
diately attacks the under-surface of each sphere, producing 
an annular ring of nitrate of mercury. A short tube is 
thus formed, sustaining the metallic globule. As liquids 
rise in capillary tubes, but do not overflow the orifice, the 
periphery of the sphere is acted upon by the nitric acid, 
-and lifted higher and higher by the deposited nitrate. 
The result is a tube of about twenty-five millimetres (one 
inch) in height, terminated by a minute sphere of mercury. 
The cross-section of the stalactite is tubular; often, how- 
ever, partially filled with interlacing crystalline planes. 
If nitrate of mercury is deposited more rapidly on one 
side, a twist is given, and a spiral tube is formed. Often 
* Proc, Geo, Soc. 1865, 413. 
a thin wall on one side predisposes the direction, and a 
curved stalactite is produced. 
It is well to consider briefly the stalactites that appear 
to have been formed mainly by deposition from water 
running over their surface. Of this class the siliceous 
stalactites well repay examination, Silica occurs in 
stalactite tubes of crystalline silicic anhydride, as in the 
specimens from Malwa, in Central India. 
The chalcedonic form, however, is far more common, 
and the specimens from Trevascus Mine afford beautiful 
examples. The tubes are generally about two to three 
millimetres in diameter, and if a section through the 
length of the tube be made, the following structure will 
be easily made out by a hand lens or one inch objective. 
Firstly, we observe a slender opaque thread with a tube 
running down its entire length; over this opaque thread 
there is a covering of chalcedony. Frequently, but not 
invariably, the junction is marked by a vesicular structure. 
_ Tounderstand this it is necessary to turn to the arti- 
ficial production of an aqueous solution of silica. By 
NITRATE OF MERCURY STALACTITES 
bringing together 112 grammes of silicate of soda, 67-2 
grammes of dry hydrochloric acid, and 1 litre of water, 
and dialysing for four days, a solution containing 4°9 per 
cent. of silicic anhydride remains upon the dialyser ; the 
chloride of sodium and excess of hydrochloric acid having 
diffused away. This solution becomes pectous somewhat 
rapidly, forming a solid jelly which dries in air into a 
glassy, lustrous hydrate. A solution containing o°5 per 
cent. of silicic anhydride remains permanently limpid. 
The minutest trace of a soluble carbonate, or a bubble 
of carbonic acid, causes a solution of silica to gelatinise 
rapidly. Professor Church has shown the importance of 
this fact in the formation of siliceous pseudomorphs of 
corals. By passing water containing 0715 per cent. of 
silica, dissolved carbonic acid, and air, over the coral, he 
replaced the carbonate of lime by hydrated silica. 
In the Trevascus stalactite under consideration, pro- 
bably the opaque thread was originally carbonate of lime. 
The carbonate would have arrested and gelatinised the 
silica, the covering thus produced affording a colloid sep- 
tum for the diffusing away of crystalloid salts. 
This view is supported by the vesicular junction with the 
chalcedonic layer, as the escape of carbonic acid would pro- 
bably have produced bubbles in the yielding jelly. Whether 
this be so or not, it is easy to convert stalactites of arra- 
gonite into siliceous pseudomorphs that present a close 
resemblance to the natural mineral. 
W. CHANDLER ROBERTS 
THE SHARPEY PHYSIOLOGICAL 
SCHOLARSHIP 
WE are most pleased to report that the movement for 
the establishment of a “Sharpey Physiological 
Scholarship” at University College, in honour of Prof. 
Sharpey, is meeting with all the success that it deserves. 
Already, by the more or less private efforts of the 
