NATURAL SCIENCES OP PHILADELPHIA. 
178 
it was considered to be a double sulphate of potash and ammonia, (the 
potash, I then thought, was in excess,) and anhydrous, (in this judging er- 
roneously from the form). 
The composition is now definitely determined by a thorough quantitative ex- 
amination, which, by the courtesy of Dr. F. A. Genth, I have made in his labo- 
ratory, and whom I here thank, for the facilities afforded me in the investi- 
gation of this new mineral. 
Lecontite occurs in crystals varying greatly in size, some being an inch in 
length and narrow prisms ; others are short, not exceeding one-eighth of an inch 
in length and quite broad. The smaller crystals are more perfect in form than 
the larger ones, and the angles are better defined. 
The following are the measurements of Prof. Dana ; the crystals he mentions 
did not admit of measurement by a reflected image, so that it was necessary to 
use a candle : 
Trimetric or right rhombic prism — 
i2 : I =160'* by measurement, 
: ie= 12*?° 30^—128° (or over n, 52° — 52«* 30' 
/: / (calculated from e^: i2 = {.Hlf/^ZlS 
The faces / are small and indistinct except on one side. 
Taking It: lz= 128° we have /: 1=^ 103° 12' 
0: H= 117° 7' 
I4 hardnesss the crystals of Lecontite are from 2- to 2-5 ; when free from 
the exterior organic matter they are clear and colorless ; the smaller crystals 
are coated with a thin crust of organic matter from the matrix. 
Taste saline and rather bitter. Permanent in the air; they contain as follows ; 
Ammonia, per ct. 12-94 contains oxygen 3-981 
Potash, " 2-67 " " 0-45 }-8-93. 
Soda, " 17-56 " » 4-50 J 
Sulphuric acid, " 44-97 " " 26-94 
Water, " 19-45 " " 17-28 
Organic residue, " 2-30 
Inorganic residue, " 0-11 
Phosphoric acid, " a trace 
There is consequently an oxygen ratio of ammonia, soda and sulphuric acid and 
water, according to the numbers 8-93 : 26-94: 17-28, which is almost exactly 
as 1:3:2, from which we have the general formula RO SO3 -j- 2H0, and 
from this the specific formula (as Prof. Dana would write it) 2NH4 0, SO3 -f-o 
(NaO, KO) SO3 + 10 HO 5 or ( ] NH4 0 1 NaO, KO) SO3 + 2H0). 
[It may be interesting to mention that there is an artificial salt, with a for- 
mula exactly corresponding to this, and of the same form, which, though rare, 
has been described by several chemists; it contains no potash, being solely ». 
double sulphate of ammonia and soda, with the two equivalents of water, as 
mentioned above. It is described in Gmelin, Vol. Ilf., p. 119, (Cavd. Edit ) : 
Seguin, Ann. Chem., 91, 219 ; Riffault, Ann. de Chem. et Phys., 20, 432 and 435 
describe the salt and its formation, and Berzelius (3, 286) mentions that the 
crystals are derived from right rhombic prisms. In Rammelsberg's Krystallo- 
graphische Chemie, p. 234, there is a figure and measurements of a trimetri<- 
(or right rhombic) crystal of a double sulphate of ammonia and soda, with four 
equivalents of water,* (NH4 0, SO3 + NaO, SO3) -f 4H0 ; it is from a descrip- 
* The formula, as Written in Rammelsberg's Krystallographische Chemie, is : — 
" (Na S -f- Am. Sj + 4 aq." I am indebted to a friend for the extract from this valuabk 
work, there not being a copy of it to be found in Philadelphia, 
1858.] 
