300 DR. KANE ON THE CHEMICAL HISTORY OF ARCHIL AND LITMUS. 
purple colour, without any trace of blue. It is not volatile, and yields, when heated 
strongly, the usual products of decomposition of substances which contain no azote, 
from which substance its analysis shows it to be completely free. With metallic 
salts it generates fine purple lakes by double decomposition. It will be at once seen 
that in all these properties it identifies itself with the substance detected in archil 
termed erythroleic acid; it is, however, more easily fusible, and, as will be now seen, 
differs in constitution. 
The analysis of many specimens of this substance, prepared at different times, and 
with different parcels of litmus, furnished results somewhat discordant as to the 
quantity of oxygen, which they indicated this substance to contain, but giving 
constantly the same relation between the carbon and the hydrogen, as has 
been already shown to exist in the erythroleic acid ; and I ultimately met with a 
quantity of this substance, which I consider to have been pure, and which although 
small, yet gave a result so definite and characteristic, that I shall detail it as express- 
ing the true constitution of this remarkable body. It furnished the largest amount 
of carbon I obtained in any instance. 
0‘283 gramme of material gave 0'760 of carbonic acid, and 0-272 of water. 
These numbers indicate the formula C 26 H 22 0 4 , by which the results are as follows : 
26 Carbon . 
Theory. 
158-6 74-43 
Experiment. 
74-27 
22 Hydrogen 
22-0 
10-33 
10-68 
4 Oxygen . 
32-0 
15-24 
1505 
2126 
100-00 
100-00 
In order to test this formula by the analysis of the compound of erythrolein with 
oxide of lead, I prepared a portion of it by precipitating the solution of erythrolein 
in ammonia, by means of a solution of acetate of lead. The fine purple lake which 
was produced was dried at 212° in Liebig’s apparatus, and then analysed. The result 
did not give any simple relation between the oxide of lead and the equivalent of ery- 
throlein, owing probably to the accidental omission of the precautions I have already 
noticed as being necessary in preparing salts of this kind, but the organic matter had 
exactly the same composition as was given in the first experiment ; there did not 
appear to have been any replacement of water. 
The formula of erythroleic acid being C 26 H 22 O s , it will be at once seen that the 
erythrolein contains half as much oxygen to the same hydrogen and carbon. Indeed, 
I consider the fluctuations in the results of my analyses of erythrolein and erythro- 
leic acid, which for a long time gave me great trouble and embarrassment, to be 
caused by their simultaneous presence as products of the same chain of reaction. In 
archil the erythroleic acid appears to preponderate, as the mixed erythrolein from 
archil seldom gives above 67 per cent, of carbon, whilst in litmus the erythrolein, 
when analysed, seldom gives a value for carbon below 70 per cent., and generally 7 2 
