1012 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
[June 21, 1873. 
it does away with the use of strong alkali, which is 
not only difficult to distil on account of humping, but 
unless great care is taken frequently introduces more 
nitrates than are originally present in the water. 
Alkaline chlorates and iodates are reduced by zinc 
and copper to chlorides and iodides, which are after¬ 
wards estimated by the usual volumetric or gravi¬ 
metric methods. 
ACTION OF GASEOUS AMMONIA UPON NITRATE 
OF AMMONIA.* 
BY E. M. RAOULT. 
If a current of dry ammonia gas be directed upon crys¬ 
tals of nitrate of ammonia, the salt melts, absorbing the 
gas, as ice would do. This phenomenon is produced under 
ordinary pressure at all temperatures between — 15° C. 
and -j-25°G. The liquid obtained is colourless. Exposed 
to the air, it loses at first a part of its ammonia, and de¬ 
posits crystals containing one equivalent of the gas to one 
equivalent of the salt; these crystals in their turn lose 
their ammonia by a prolonged exposure to the air, and at 
length only pure nitrate of ammonia remains. 
The composition of the liquid in question varies with 
the temperature. At 10° below zero 100 grams of nitrate 
of ammonia absorb 42'50 grams of ammonia gas; conse¬ 
quently the product formed at this temperature contains 
one equivalent of the salt combined with two equivalents 
of the gas, and corresponds to the formula NH 4 ,N0 3 -f 
2 N H 3 . It is not frozen by a mixture of ice and salt. 
Its sp. gr. is P05. Heated, even slightly, this ammo- 
niacal nitrate is decomposed. It boils with loss of am¬ 
monia, and at about 28 - 5° C., under the ordinary pressure 
of 760°, it is transformed into a crystalline mass, contain¬ 
ing 21'25 grams of the gas combined with 100 grams of 
the salt, and corresponding consequently with the formula 
nh 4 ,no 3 +nh 3 . 
This new ammoniacal nitrate, which is solid, is broken 
up in its turn, if heat be continued, and at 80° C. there is 
left a residue of pure nitrate of ammonia. 
The following are the exact quantities of ammonia 
absorbed by 100 grams of nitrate of ammonia, under a 
pressure of 760° and at different temperatures :— 
Temperature. 
— 10 deg. 
0 
55 
+ 12 
55 
18 
55 
28 
55 
29 
55 
30*5 
55 
40-5 
55 
79 
55 
Gas absorbed. 
.. 42-50 
grams. 
.. 35-00 
55 
.. 33-00 
55 
.. 31-50 
55 
.. 23-25 
55 
.. 20-90 
55 
.. 17-50 
55 
.. 6-00 
55 
.. 0-50 
55 
State of product. 
... liquid. 
... liquid. 
... liquid. 
... liquid. 
... liquid. 
... solid. 
... solid. 
... solid. 
... solid. 
These ammoniacal nitrates, as will be seen, are analogous 
to the ammoniacal chlorides, and, like them, decompose 
easily. 
An aqueous solution of ammonia dissolves much more 
nitrate of ammonia than pure water does. The absorbent 
power of the salt for the gas is therefore not diminished 
by the presence of water. On the contrary, a solution of 
nitrate of ammonia in water absorbs a little more am¬ 
monia gas than the water and the salt it contains would 
do separately. At temperatures between zero and -j- 20° C. 
the coefficient of the solubility of the gas is the same in 
water and in the saline solution, and, what is no less re¬ 
markable, the heat due to the absorption of the gas is 
almost identical in both liquids. 
The liquid and anhydrous ammoniacal nitrate of am¬ 
monia, prepared and kept as much as possible at a low 
temperature, constitutes a new reagent and solvent, low 
in price and easily manipulated. It can be used for the 
rapid production of pure and dry ammonia gas, for which 
* 1 Comptes Rendus,’ vol. lxxvi. p. 1261. 
it only requires slightly heating. It can be used also, 
under the guise of an ammoniacal chloride of silver, for the 
liquefaction of ammonia gas in a Earaday’s tube; it yields 
in fact one-third of its volume of liquid ammonia, pro¬ 
vided only that one of the branches of the tube be kept at 
100° C. and the other at zero. Its decomposition, how¬ 
ever, is not complete under these conditions ; it still con¬ 
tains one equivalent of ammonia combined with one 
equivalent of the salt, and upon cooling forms a white 
crystalline mass. 
TEE SILPHIUM OF THE ANCIENTS* 
BY A. S. OERSTED. 
In a paper originally published in the ‘ Overs, over de 
K. Danske vid. selsk. Forh.’ for 1869, of which a German 
abstract appeared lately in the ‘ Zeitschrift fiir Ethno- 
logie’ (1871, pp. 197-203), the author gives a history of 
our knowledge of the silphium plant of antiquity, and the 
results of modern researches directed to the determination 
of its nature. 
In the middle of the seventh century b.c. some Greeks 
from the island of Thera settled on the north coast of 
Africa, in the district then called Cyrenaica, and now 
known as Barka. The state which was subsequently de¬ 
veloped owed its great commercial prosperity very largely 
to its trade in silphium, and the numerous coins found in 
the district bear on one side the head of Jupiter Ammon, 
and the silphium on the reverse. This plant grew wild 
in the uncultivated southern part of the country, and did 
not succeed under cultivation. From its root when sliced 
a milky juice exuded, which, when dried or mixed with 
meal, formed that costly spice which was so highly valued 
by tl' i Greek and Roman gourmets , and was also in high 
repute as a medicine. Silphium fetched its weight in 
silver, and was reckoned with other precious things in the 
Roman state treasuries. During the decline of Cyrenaica 
the production of silphium gradually decreased; the 
country first fell into the hands of the Ptolemies (322 B.C.), 
and afterwards became a Roman province. In 61 B.C. 
30 lbs. of silphiunFwere brought to Rome; and the Em¬ 
peror Nero had a specimen of the plant sent to him as a 
curiosity. It was still known in the fifth century A.D.; 
Synesius, who, when he died in 431, was Bishop of Barka, 
mentions that he supplied a friend with a specimen of the 
rarity. The reason of its decrease is said by Strabo to 
have been an incursion of nomadic barbarians who laid 
the country waste. The farmers also let their cattle feed 
upon it.+ 
Much has been written as to the nature of this remark¬ 
able plant, which, from the description and the figures on 
the coins, has always been known to be an umbellifer. 
Modern travellers who have visited Barka (now an alto¬ 
gether desolate land, with numerous ruins of towns and 
temples), such as Della Celia, Pacho, Barth, the brothers 
Beechey, and more lately Rohlfs, have considered a com¬ 
mon umbellifer which the natives call drias {Thapsia Sil¬ 
phium, Viv., Laserpitium Derias, Pacho; according to 
Cosson (Bull. Soc. Bot. Fr. 1865, p. 277) merely a form 
of the South European Thapsia garganica , L.) to be the 
silphium plant; but neither its appearance nor its proper¬ 
ties bear any resemblance to those of that plant. The 
celebrated plant of antiquity was wholesome to cattle; 
the drias is poisonous and has frequently proved fatal to 
camels. Various other species have been suggested by 
authors:— Ferula tingitana, L., by Sprengel; Laserpitium 
gummiferum, Desf., by Link; Ferula Assafcetida, by the 
Diet. d’Hist. Nat.; and Laserpitium Siler, L. 
Prof. L. Muller, when engaged in his work on the coins 
# From the Journal of Botany, June, 1873. 
f For an exhaustive account of all that can be read in 
the ancient authors on the silphium plant, reference may 
be made to Thrige’s ‘ Res Cyrenensium ’ (Hafnise, 1828), 
pp. 304-315.— [Ed. Journ. Bot.'] 
