June 7, 1873.] 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. 
973 
to 12 feet, with a stalk of from 1 to 1| inch in diameter, yet exactly defined, so there exists little precise informa- 
The flowers appear about the end of July and continue tion respecting the physiological phenomena attending the 
throughout August. The capitulum only expands during formation of the gum itself. It is known that the abnor- 
sunshine, and as when in fruit the least breath of air wafts 
away the pappose achenes, the collection of seed is a 
matter of constant anxiety and attention. In one wet 
and sunless autumn I was unable to secure a single seed, 
none having ripened. 
In favourable seasons the collection of the juice may 
commence about the middle of July, but it more com¬ 
monly is the beginning of August before anything is done. 
The plants are then 3 to 5 feet high, with thick succulent 
stalks, and the flower-buds just appearing. The collectors 
proceed over the field, cutting the head of each stalk, and 
scraping the flow of juice into their vessels—one person 
cutting being followed by two collecting the juice. This 
process they repeat six or seven times a day, each time a 
new cut being made a little lower down the stalk. The 
period of collection generally lasts from six weeks to two 
months, closing usually about the third week in Septem¬ 
ber ; but for the last two years -I collected up to the end 
of September. Towards the close of the season the plants 
become so woody and hard that it is with great difficulty 
new cuts can be made for the flow of the juice. About 
this time the frosty nights seriously influence the flow of 
the juice, and determine the cessation of the year’s collec¬ 
tion. The juice after frost usually becomes of a watery 
consistence, and when it remains thick, as it sometimes 
does, it is so deteriorated in quality as to be worthless. 
The amount collected during the day is by the evening 
changed into a thick viscous mass. It is then turned out 
of the vessels, divided into pieces suitable for drying, and 
spread out to the influence of a fire, as the sun heat in our 
climate is not sufficiently strong for the drying process. 
The time occupied in drying varies according to the heat 
applied, but I obtain the best results in about five days. 
As regards the yield of lactucarium much depends upon 
the season. In rainy weather no collection can be made ; 
moist warm weather causes the greatest flow of juice, 
while in dry, hot seasons the stalks are slender, the yield 
of juice small, but usually of very superior quality. So 
much does the yield vary that in some seasons the collect¬ 
ing vessel of 8 or 9 oz. capacity is not more than half 
filled daily, and in other years three such measures-full 
are gathered each day. Generally six such measures, 
equal to a little more than 4 lb. of thickened juice, yield 
1 lb. of solid lactucarium. On an average I calculate 
each plant yields 40 or 50 grains of lactucarium, but this 
estimate includes plants of all descriptions. Were the 
really healthy and productive plants only taken into 
account, the average yield would be much greater. 
A very small quantity of lactucarium is now used in 
the medical practice of this country, and I do not know 
the source of the demand which I am annually called on 
to supply. 
For many reasons lactucarium cultivation is a preca¬ 
rious industry. Besides its dependence on rainy or dry 
weather, wind is fatal to the plants in all stages after the 
stems have shot up. From their first appearance, the 
plants are also peculiarly liable to be attacked at the root 
by a species of grub, which causes great havoc. 
GUM ARABIC.* 
BY DR. GRAEGER. 
Formerly gum arabic was generally considered to be 
a vegetable principle, similar to sugar and starch, and it is 
not many years since Fremy for the first time called the 
attention of chemists to the special relations which existed 
between the organic substance of the gum and the mineral 
elements or residues of its ash. The researches of Fremy 
relative to this question not being generally known, a 
brief resume of them may be given here. 
Just as the part played by its inorganic elements is not 
* ‘Neues Jalirbuch fiir Pharmacie,’ xxxviii. 129. 
mal formation of gum in certain ti*ees takes place at cer¬ 
tain periods, at the same time as that of the ligneous parts 
and at their expense; but it is not known to the trans¬ 
formation of what matter the production of gum is due. 
One thing is surprising that a neutral substance like it 
should proceed from an acid fruit. 
It had previously been remarked that under certain cir¬ 
cumstances, gum submitted to the action of concentrated 
sulphuric acid was changed into a new body entirely in¬ 
soluble in water. This takes place when an aqueous 
solution of gum, so concentrated that it will scarcely run, 
is poured into a suitable vessel containing strong sulphuric 
acid,—care being taken not to mix the two liquids,—and left 
in contact for several hours. The gum is changed into a 
kind of membrane that is insoluble even in boiling water. 
If water and a slight quantity of some alkali be added, 
and the mixture slightly heated, this substance dissolves 
into a clear liquid, from which it is not precipitated by an 
acid, showing that it has undergone a new modification by 
which it has again become soluble. The insoluble mem¬ 
branous substance was named by Fremy metagummic 
acid; the soluble modification of it as changed by alkalies 
has received the name of gummic acid. Ordinary gum 
arabic then contains a substance insoluble in water,—me¬ 
tagummic acid,—which like oenanthic and lactic acids 
loses its insolubility by the action of alkalies, and is trans¬ 
formed into gummic acid, combining like them with the 
alkali to form a true salt. 
These data of Fremy have to the present time neither 
been contradicted nor confirmed ; they have been little 
noticed, although there can be no doubt that they would 
be of great importance to vegetable physiology. 
In taking up the investigation the author proposed first 
to determine with precision the bases combined with the 
gummic acid, and also to find a method of preparing pure 
metagummic acid, that employed by Fremy not appearing 
to be sufficiently practical, since it is always difficult to 
free the viscous mass from the last traces of sulphate of 
lime and sulphuric acid. 
Analysis was made of some picked gum, clear and free 
from powder. Gum dried in the air was found to contain 
11'6 per cent, of water, the composition being— 
Organic matter. 85"25 
Ash.. 8-15 
Water. 11 '60 
The composition of anhydrous gum was— 
Ash .. 3-563 
Organic matter. 96’437 
The ash was analysed, with the following result:— 
I. 
II. 
III. 
Lime . 
. 46-70 ., 
,. 54-63 
... 44-53 
Magnesia . 
. 12-61 .. 
,. 14-38 
... 26-18 
Potash . 
. 40-69 . 
.. 30-99 
... 29-29 
These constituents, calculated as potash, are equal to 
the following amounts of that base— 
I. II. HI. 
128-27 ... 134-10 ... 122-91 
Adopting 3'563 per cent, as the average quantity of 
ash contained in dried gum, it appears that 96"437 parts 
of organic matter were combined with an average of 4'45 
parts of potash or 2*644 parts of lime. 
It is not surprising, says Fremy, that gum, which is a 
salt of lime, contains only 3 per cent, of that base. Gum¬ 
mic acid has a very feeble capacity of saturation, which is 
generally the case with all the gelatinous acids in propor¬ 
tion as they approach organic vegetable products ; their 
capacity of saturation augmenting in proportion as, trans¬ 
formed by chemical means, they depart from their primi¬ 
tive organic form. . 
The numbers given above coincide with the results of a 
great number of experiments, showing that the propor- 
