536 
THE PHARMACEUTICAL JOURNAL AND TRANSACTIONS. [December 30,1871. 
"by ether. On evaporating this solution, there remained 
a residue, from which he isolated a substance which he 
called lecanorine or lecanoric acid. This compound crys¬ 
tallizes in white needles, and gives a red colour with 
blcaehing-powder, and a dark purple with perchloride 
of iron. It yields a similar colour wdicn dissolved in 
ammonia and exposed to the atmosphere. Its most 
interesting property is its conversion into orcine and 
carbonic acid when boiled with an aqueous solution of 
baryta. The reaction is— 
C 8 H 9 0 4 = C 7 H 8 0 2 + C0 2 . 
Lecanorine. Orcine. Carbonic acid. 
He found also that on boiling lecanorine with alcohol 
it formed an ether, which proved to be identical with the 
pseudo-erythrine of Heeran. 
Dr. Stenhouse has succeeded in extractin'? the im- 
portant compounds to which he has given the names of 
erythrite and orsellic acids. The first-mentioned body is 
a product of the decomposition of erythrine under the 
influence of limc-w r ater. The erythrine splits up into 
carbonic acid, orcine and erythrite, according to the 
following equation:—• 
C 12 II iq 0 7 + H 2 0 
Erythrine. ' 
= c 4 h 10 o 4 + c 7 h 8 0 2 + co 2 . . 
Erytlirite. Orcine. Carbonic acid. 
The orsellic acids w~ere obtained, one from the South 
American weed, the other from the South African. The 
first appears to be identical in composition with lecano¬ 
rine, and is capable of splitting up under the influence 
of baryta or lime into carbonic acid and orcine. The 
one from the latter appears to be composed of lecanoric 
acid and a substance called roccellinine. According to 
Schiitzcnberger, lecanoric acid may bo made to undergo 
a decomposition into orsellic acid, or may be further 
converted into orcine. 
The employment of orchil is at the present day com¬ 
paratively limited, but it is still used for producing 
browns, maroons and other dark shades, in conjunction 
wdth other dye-stuffs. Its chief use is to top cheap 
indigo blues on woollen goods; this is effected by lightly 
dyeing the fabric with indigo (an expensive dye), and 
then passing it through a bath of orchil, which gives to 
the cloth a rich purple hue, similar in appearance to one 
dyed wdiolly with indigo. 
Cudbear is a special preparation of orchil, first manu¬ 
factured by Dr. Cuthbert Gordon, from whom it derives 
its name. 
Litmus is obtained from the same lichens as those 
employed for producing orchil, only lime and carbonate 
of potash are added to the ground weed and urine ; in 
fact, the process is very similar to that used in former 
times to produce orchil. After three or four weeks, a 
blue colour is fully developed, when it is mixed with 
sulphate of lime or chalk, dried, and is ready for market. 
The chief employment of litmus is to communicate a 
peculiar tint to the cheese made in Holland. 
Prussian Blue. —I shall now have the pleasure of draw¬ 
ing your attention to one of the finest, brightest and 
most permanent colours known. It was discovered 
accidentally in 1710 by a colour manufacturer named 
Diesbach, of Berlin, from which it derived its name. The 
process by which it was produced was kept a comparative 
secret until 1724, when Dr. Woodward showed how the 
colour had become a very profitable affair, and described 
a process by which it could be obtained. The process 
has in time undergone many improvements; but I shall 
here confine myself to a description of it as now carried 
out. I shall be obliged here to enter slightly into 
theoretical chemistry. 
Prussian blue is a combination of iron with cyanogen , 
a compound of carbon and nitrogen. There are two well- 
defined cyanides of iron corresponding to the two oxides, 
the proto-cyanide, EeCy, and the sesquicyanide, Fe 2 Cy 3 . 
These two cyanides, combining together in different pro¬ 
portions, give rise to the various shades of Prussian blue- 
found in commerce. But, strange to say, you cannot 
produce either of these compounds, or Prussian blue, by 
the direct combination of cyanogen with iron. Cyanogen 
must be first united with potassium, giving rise to cyanide 
of potassium, under the influence of which salt the iron 
combines with cyanogen, and the cyanide of iron thus 
formed in its turn combines with the cyanide of potas¬ 
sium, forming a double cyanide. There are two double 
cyanides of potassium and iron ; the first, called ferro- 
cyanide of potassium, or yellow prussiato of potash; the 
second, ferri-cyanide, or red prussiato of potash. The 
formula may be represented as follows :—• 
Yellow prussiate. . Fo Cy -f- K Cy 
Red prussiate . . . Fe 2 Cy 3 + 3KCy. 
To produce Prussian blue from these salts, it is neces¬ 
sary to replace the potassium by iron. This is effected 
by adding a pcrsalt of iron to the yellow prussiate, or to 
the red prussiate a proto-salt of iron. The iron of the 
iron salt replaces the potassium of the double salts, and 
double cyanides of iron are produced, a3 seen by the fol¬ 
lowing formulae:— 
3 (FeCyKCy) + Fe^b, = 3FeCyFe 2 Cy 3 
Yellow prussiate. Sesquichloride Prussian blue. 
of iron. 
+ 3KC1. 
Chloride of potassium. 
Fe 2 Cy 3 K Cy + 3FeCl = Fe 2 Cy 3 3FeCy 
Eed prussiate. Protoehloride Prussian blue, 
of iron. 
+ 3 K Cl. 
Chloride of potassium. 
That this is the case can be easily demonstrated, for if 
you mix together a solution of pcrsalt of iron and one of 
red prussiate, which contains only pcrcyanide of iron,, 
no Prussian blue is formed. Again, if you mix yellow 
prussiate of potash with protochloride of iron, you get 
no Prussian blue, because, in the first case, you have no 
protocyanide of iron present, and, in the second, you have 
no percyanide. 
Simple as the production of Prussian blue appears, it 
requires much practice to prepare it with certainty as a 
pigment wdiere a given shade of blue is required. It is 
seldom found pure in commerce, being generally mixed 
with starch, chalk or gypsum. Sometimes they are 
added with a view to deception, sometimes in order to 
produce a lighter shade of colour. The testing of a 
Prussian blue by chemical means is not, therefore, a 
true criterion of its quality. The method usually em¬ 
ployed consists in grinding in oil equal weights of a 
Prussian blue of known value and of the one to be tested, 
white lead is added to each, and the intensity of the 
colours compared. 
The best quality of Prussian blue is obtained by mix¬ 
ing a dilute solution of red prussiate of potash with proto¬ 
salt of iron; the second quality is made by mixing yellow 
prussiato of potash with pernitrate of iron, and is called 
Turnbull's blue. Cheaper qualities are made by mixing 
solutions of yellow prussiate and protosulphate of iron 
(green copperas), which produces a pale blue precipitate. 
This is transformed into Prussian blue by the addition 
of bleaching-powder, which oxidizes part of the iron, 
and transforms the protocyanide into pcrcyanide. For 
still lower qualities, alum is mixed with the iron solu¬ 
tion previously to the prussiate being added. Alumina 
is by this means mixed wdth the bhie. 
Prussian blue was first obtained on silk fabrics in 
1811 by a professor of chemistry at Lyons, named Ray¬ 
mond, in consequence of the high premium offered by the 
first Napoleon for the production of a fast blue, as indigo 
could not at that time be imported into France. His 
process, with slight modifications, is follow T ed at the pre¬ 
sent day, although the colour is not much used, owdng 
