Page:Proceedings of the Royal Society of London Vol 1.djvu/468

Rh resinous matter no longer soluble in water, but now rendered soluble in alcohol, by a supposed union with oxygen derived from these acids.

Mr. Smithson being in possession of ulmin, sent to him from Palermo by the same person who had furnished M. Klaproth with the subject of his researches, has made various experiments, which lead to a different opinion of its nature from that which has been entertained.

When ulmin is dissolved in water, a dilute solution is yellow; but when concentrated, it is of a dark red, like blood. This solution slowly and feebly restores the colour of turnsol, after it hasbeen red- dened by an acid. Most acids occasion a copious precipitate from this solution of the matter which has been considered as resin. The solution, however, still retains a. slight yellow colour, from a small quantity of this matter which remains dissolved. By evaporation of the solution a salt is obtained, consisting of potash combined with the acid employed in the experiment; and the quantity of potash, by various trials, amounted to about one ﬁfth part of the weight of the ulmin.

The precipitate, when dried, is very glossy, and has a resinous appearance. In minute fragments it is found to be transparent, and of a deep garnet colour. It burns with ﬂame, and is reduced to a white ash.

Alcohol does dissolve it, but very sparingly.

Water also dissolves a small quantity, and the solution seems to redden turnsol. Neither ammonia nor carbonate of soda promote its solution in water; but a small quantity of potash dissolves it immediately, and abundantly, and appears to regenerate ulmin. with all its original properties.

Hence Mr. Smithson infers, that ulmin is not a simple vegetable principle of anomalous qualiﬁes, but a combination of potash, with a matter more nearly allied to the extmctives than to the resins.

The author has also investigated the properties of a substance ob- tained from the elm-tree in this country, which diﬁ'ered from that of Palermo in containing a redundant quantity of potash in the state of carbonate. He also made experiments on the sap of the elm-tree, from which, however, he did not succeed in obtaining ulmin.

The method here described by the author, is performed by means of an instrument, to which he gives the name of Cryopborus, expressing its ofﬁce of frost-bearer. It consists of a tube, which may be two or three feet long, or even more, terminated by a ball at each end. One of these balls contains a small quantity of water to be frozen, and the rest of the instrument is as complete a vacuum as can be obtained

in making this instrument, one of the balls terminates in a capillary