72 
MR. STENHOUSE ON THE EXAMlNiiTION OF THE 
The results of these analyses agree pretty closely with the formula CggH^yOig, 
which however is merely empirical. I have made many attempts to determine the 
atomic weight of roccellinin by endeavouring to combine it with the alkalies and 
earths so as to form definite salts, but hitherto without success. It produces no 
precipitate with acetate or subacetate of lead, or with nitrate or ammonio-nitrate of 
silver. When a current of chlorine gas was passed for four days through a quantity 
of roccellinin diffused through water, the roccellinin assumed a slightly yellow colour. 
It was collected on a filter and washed to free it from adhering muriatic acid ; when 
crystallized out of alcohol its properties were unchanged, and when subjected to 
analysis it contained no chlorine. Nitric acid in the cold had no action upon it, 
with the assistance of heat it converted it into oxalic acid. An attempt was made to 
prepare a baryta salt by boiling the roccellinin with freshly-precipitated carbonate of 
baryta. A quantity of prismatic crystals were obtained, but the quantity of base 
they contained varied according to the concentration of the solution. With caustic 
baryta, magnesia and lime, the results were equally unsatisfactory. When dissolved 
in an excess of ammonia and dried in vacuo, it was found to be unchanged, and to 
contain no ammonia. Roccellinin appears therefore to be a very indifferent body, 
which, like santonin, enters into no stable combinations with either alkalies or 
acids, though it appears to have a slight affinity for bases, and may therefore be re- 
garded as a feeble acid. I am quite unable to determine what relation roccellinin 
bears to the orsellic series of acids, with which, however, it is not improbably con- 
nected, as the (beta) orsellic acid appears to be partially replaced by it in the Cape of 
Good Hope lichen. 
Roccella Montagnei. 
This lichen, which is imported in large quantity from the Portuguese settlement of 
Angola, and also from Madagascar, where it grows upon trees, was examined by 
Mr. ScHUNCK under the name of Roccella tinctoria var. fuciformis. Dr. Scouler 
pronounces it to be the R. Montagnei of Betenger, who* found it growing on 
mango trees at Madras. The branches of the true R. fuciformis are much rounder 
than those of the R. Montagnei, which are nearly quite flat. This lichen is by much 
the richest in colouring matter of any of those employed by the archil manufacturers. 
Mr. ScHUNCK extracted its colouring principle by treating the lichen with boiling 
water, and purifying the crystalline precipitate by repeatedly crystallizing it out of 
weak spirits. This is a very wasteful process ; Mr. Schunck states that he only got 
60 grs. of erythric acid from a pound weight of lichen. The erythric acid employed in 
my experiments was prepared partly in this way, but chiefly by the more economical 
method of macerating the lichen in milk of lime, as already described. By the lime 
process, the average product of crude erythric acid amounted to twelve per cent, of 
the weight of the lichen employed. The erythric acid prepared by either method 
* See Voyage aux Ind. Orient. 
