122 
TWO HAIR SALTS DISCOVERED AT THE CAPE. 
the experiments of Dulong or the specific 
heat of compound gases applies equally to the 
specific heat of compound bodies in the solid 
state, viz, that the specific beat of the com- 
pound atom of a solid body, taking as unity 
that of a simple atom, given by the law of 
Dulong and Petit, is represented by the square 
loot of the whole or fractional number, which 
expresses the atoms or portions of simple atoms 
of different kinds, entering into the formation 
of this compound, a number, which, for brevi- 
ty’s sake, may be termed the coistituent num- 
ber of the compound atom. Consequently, to 
obtain the constant number, T875, it is neces- 
sary to multiply the specific heat of compound 
bodies (taking that of unequal weight of water 
as unity) fust by the weight of the compound 
atom, taking that of oxygen as unity, as for 
simple bodies, and to divide by the square root 
of the constituent number ; and reciprocally 
to obtain the specific heat of a solid bo<ly, 
taking as unity that of an equal weight of 
water, we must multiply the square root of 
the constituent number by * * * § *1875, and divide 
by the weight of the compound atom. It will 
now be proper to consider the afrplication of 
this law to the different kinds of compound 
bodies. 
EXAMINATION OF HAIR SALT, OR 
NATIVE SULPHATE OF ALUMINA 
AND IRON. 
By Robert D. Thomson, M.D. 
The salt known under the name of hair salt 
and feather alum, which is produced by the 
decomposition of strata containing' iron pyri- 
tes, has been examined hy different chemists ; 
but hitherto no definite composition has been 
assigned to it, notwithstanding the length of 
time which has elapsed since it was first 
noticed. 
Dioscorides presents us with a detail of its 
characters so striking as to prevent any mis- 
take in identifying it.* IIS describes it as 
being very white, astringent, in capillary pior- 
tions, which resemble what was called in 
Egypt trichitis. Pliny likewise mentions it 
particularly : “ Concreti,” says he, “ alumi- 
nis unum genus schiston appellant Graeci, in 
capillamenta quredam canescentia dehiscens. 
Undequidem tricliitin potius appellaver. Hoc 
fit e lapide ex quo et chalcitin vocant,” 
The indefatigable Tournefort visited the 
island of Milo, from which the salt described 
by these ancient authors was derived, and has 
satisfied us that the characters, as givezi by 
Dioscorides and Pliny, are quite accurate. J 
I. Klaproth examined a salt of a greyish- 
white colour becoming yellow hy exposure to 
the air, occurring in alum state, and found 
its chemical composition to he Alumina 15*25, 
Protoxide of iron 7 ’50, Potash *25, Sulphuric 
acid and water 77, total 100*§ 
If we consider the alumina and iron to be 
saturated the constituents will he, Alumina 
* V. 323 
i Piin Nat. Hist. xxxv. 16. 
t Tournefort’s Voage 177. 
§ Beitrage, iii. 103, Chemische Uutei'suchung 
des federalaujis von Freyen^yalde. 
15*25 7, Protoxide of iron 7*5 1. Sulphuric i 
acid 41*77 8, Water 35*48 31, total 100*00* 
equivalent to 7 Al. S. -{-31. Aq. 
2. The same chemits states that the hair i 
salt from the mercurial mines of Idria, (Ha- I 
lotrichum Scopolii), found in alum slate, j 
possesses a silvery white colour, and consists ( 
essentially of sulphate of magnesia, united 
with a small portion of sulphate of iron. Ac- | ) 
cording to a recent analysis hair salt from c 
Idria consists of 
Magnesia 16*389 - 1 atom. ; 
Protoxide of iron. . 0*226 - 
Sulphuric acid 32*303 - 1 ,, 
Water 50*934 - 7 atoms i 
99*852t 
which answers to MS. 7 Aq. mixed with a 
little sulphate of iron, agreeing exactly in i 
composition with the right prismatic crystals ! 
of the common Epsom salt. A similar mine- 
ral from Calataynd, in Arragon, yielded, 
Magnesia 16*495, Sulphuric acid 31*899, 
Water 51*202, 99*596 
3. Berthier has published the analysis of a 
hair salt, (Thomson’s Inorganic Chemistry, 
ii. 768.) consisting' of Sulphuric acid 34*4, 
Protoxide of iron 12* Alumina 8*8, Magne- 
sia 0*8 Water 44* 100* corresponding with ^ , 
Al. S. 4-/8. -1- 15 Aq.J 
4 In the course of an excursion to the 
eastern parts of the colony of the Cape of 
Good Hope, H. Hertzog discovered two hair 
salts in a cave on the Bushman River, 200 . 
feet above its bed, in 30» 30' S.L. and 26" 40' 
E.L., twenty miles from the sea. The cave 
was thirty feet wide, seven feet high, and 
twenty deep, having its upper part coated 
with feather alum, presenting the appearance 
of gypsum. The salt is snow-white, 
fibrous, with a silky lustre, the darker coloured 
fibres being very elastic. The fibresare partly 
straight and partly bent. The mineral 
consists, according to H. Stromeyer, of 
Alumina 11*515, Magnesia 3*690, Protoxide 
of manganese 2* 167, Sulphuric acid 36*770, 
Water 45*739, Chloride of potassium 0.205, 
100*0S6§ which is expressed hy 
2^ Al. S. -f. (I M. -p mn.) S. 20{ Aq. 
Under the alum a bitter salt is found, which 
is frequently crystallized in four-sided prisms, 
and when pure, is white. The mass accom- 
panying the bitter salt is weather-beaten, 
earthy, and has a salty appearance, and a 
greenish-white colour. It contains scales of 
mica, or talc, which are parallel with its 
cleavage. H. Stromeyer found it to contain 
silica and alumina in considerable quantity ; 
very little iron, much manganese, and one 
per cent, lime and magnesia. Water exti’acts 
from it common salt, gypsum, bitter salt, 
sulphate of manganese, and a trace of sulphate 
af alumina. 
The salt itself consists of Magnesia 14*579, 
Pi’otoxide of manganese 3*6l6, Sulphuric 
acid 32*258, Water 49*243, 99*696, correspond- 
ing with 11 MS. -J- mn S. 91 Aq. 
CTo be Continued) 
* Beitrage,iii. 104. 
t PoggendorfF, Aniialen, xxxi. 144, 
t Ann. des Mines, v. 239. 
\ Poggendorff, Ann. xxxi. 143. 
