Proceedings of the Royal Society. 
95 
A compound, prepared by adding neutral acetate of lead to an 
alcoholic solution of the colouring matter, keeping the latter in ex- 
cess, approaches the formula C 46 H 28 0 2g , 2PbO, 8HO. 
When xanthorhamine is boiled with weak sulphuric acid, it is re- 
solved into grape sugar and a yellow powder, which the author pro- 
posed to name Rhamnetine ; showing the colouring matter to be a 
giucosideo In the proportion of its constituents, its softish, nearly 
tasteless crystals, and insolubility in ether, it agrees with these bo- 
dies generally. 
The composition of rhamnetine agreed closely with the formula 
C 22 H 10 O 10 . It is almost entirely insoluble in water, alcohol, and 
ether ; alkalies dissolve it, and acids reprecipitate it from an alkaline 
solution. The ammoniacal solution precipitates metallic salts. 
On adding the formula of rhamnetine to that of grape sugar, we 
have xanthorhamnine plus 6 atoms of water. 
^22 Hio Oio + C 24 H 24 0 24 = C 46 n 28 0 28 + 6HO. 
Rhamnetine. Glucose. Xanthorhamnine. 
Quantitative determinations of the rhamnetine and glucose give 
results agreeing with this equation. 
If the formula given by Kane for chrysorhamnine be doubled, we 
have the formula of xanthorhamnine minus 6 atoms of water — 
C 46 H 22 0 22 + 6H0 = C 46 H 28 0 28 
Chrysorhamnine. Xanthorhamnine. 
3. Account of some Experiments on Radiant Heat. By B, 
Stewart, Esq. Communicated by Professor Forbes. 
The object of these experiments was to compare together the ra- 
diations from the polished surfaces of different bodies, all having 
the temperature of 212°. In order to heat the bodies, a tin box 
was used, double-sided and double-bottomed, or a box within a box. 
Water being kept boiling in the interval, the interior chamber was 
found to have a temperature of nearly 212° ; and on the bottom of 
this chamber the bodies to be experimented on were placed. When 
being used these were taken out of the chamber and placed before 
the sentient pile of a thermo-multiplier, the galvanometer needle 
connected with which was immediately deviated from its zero posi- 
tion. The extent of the first swing of this needle was taken to de- 
note the quantity of heat that fell upon the pile, and this deviation 
