1866.] | Physics. 117 
running east and west, nearly vertical and from three to six feet 
wide, is almost entirely occupied with this silicious sand of the most 
perfect purity and lustrous whiteness. 
An interesting series of experiments “On the Thermo-Electric 
Tension of Minerals,” by Walter Flight, D.Se., will be found com- 
municated to the ‘ Philosophical Magazine’ for November. 
On the line of railway from Estremadura to Portugal occur con- 
siderable deposits of Phosphate of Lime. This phosphate of lime 
attains its maximum of 85 per cent. in the formation of Montan- 
ches, six leagues from Caceres and eight miles from Logrosan, its 
minimum being about 50 per cent. This has been described by 
M. Luna.* This phosphate is found in the cretaceous strata, and 
is in great abundance in the silicious bed; it presents a fibrous 
texture. The following analyses are given :— 
Caceres, Montanches. 
Tribasic Phosphate of Lime - . 72°10 85 03 
Oxide of Iron, Silica, &e. . - - 3°85 2°40 
Water . . ° ° ° 3 00 2 7 22 
Carbonate of tiete : ; é 3 — 10°35 
Residue insoluble in Nitric Acid fs 47°02 — 
IX. PHYSICS. 
~ * Licut.—Professor Mitscherlich has greatly extended the powers 
of spectrum analysis, by applying it to the detection of the electro- 
negative elements, chlorine, bromine, and iodine. 
The difficulty of recognizing small amounts of these elements in 
a mixture of haloid salts is well known, and it is found impossible to 
detect mere traces of these bodies in such mixtures by any hitherto 
known method. The followig means, however, will recognize the 
smallest amounts of these substances by the use of spectrum apparatus. 
The haloid salts of copper are the most difficult to decompose by 
heat, and they are therefore to be preferred for spectrum investiga- 
tions, which are best made in the following way :—The substance to 
be examined, well dried, is mtimately mixed with half its weight of 
sulphate of ammonia and one-tenth its weight of oxide of copper. 
The mixture is placed in a globular enlargement of a combustion- 
tube, one end of which is connected with a hydrogen gasometer, the 
opposite end being open. A stream of hydrogen is passed through 
the tube, and heat gradually applied to the mixture. The hydrogen 
being ignited, the first appearance seen in the spectrum apparatus is 
a brightness in the green, in which, however, no definite spectrum 
can be perceived, but afterwards the spectrum of the haloid salt of 
copper is distinctly visible. 
When present in small amount, the chlorine compound is best 
* «Compte Rendus,’ 
