1813.] On a new Variety of Ulrnin. 11 



Article IV. 



On a new Variety of Ulmin. By Thomas Thomson, M. D. F. R. S. 



The experiments detailed in the first number of these Annals 

 upon the ulmin from the elm show us that it is a peculiar 

 vegetable principle, distinguished by the following properties: — 



1. Of a dark brown colour, and little taste. 



2. Soluble in water, but insoluble in alcohol and ether. 



3. Not precipitated by solution of gelatine. 



4. Precipitated brown by iron, tin, mercury, and lead, when 

 these metals are in the state of saline solutions. 



5. Precipitated by acids. 



6. Swells greatly when heated, as is the case with gum, but 

 does not melt. 



These characters do not apply to any other vegetable principle 

 at present known. Hence it is obvious that we must constitute 

 this substance a new vegetable principle. Some chemists are 

 inclined to refer ulmin to extractive; but it is high time to 

 render that very indefinite class of vegetable substances somewhat 

 more precise. Nohody has ever examined extractive in a state 

 of purity. Hence its properties are unknown, and it has been 

 customary to refer to that class all substances which could not be 

 referred to any other. It constitutes a kind of sink, or common 

 sewer, in vegetable chemistry ; but such an indefinite mode of 

 proceeding is highly injurious to the progress of this branch of the 

 science. If we wish to make ourselves accurately acquainted with 

 the vegetable kingdom, we must distinguish every substance 

 which possesses peculiar properties by a peculiar name. No risk 

 of error results from multiplying the number of vegetable prin- 

 ciples : the error into which we are most likely to run is classing 

 the most dissimilar substances under the same name ; thus 

 enabling us to satisfy ourselves and others with giving a substance 

 a name without being in the least aware of its distinguishing 

 characters. What, for example, could be more preposterous 

 than to give the same name to vegetable substances, some of 

 which are soluble, and some insoluble, in alcohol? Yet this has 

 been proposed by some of the most eminent chemists, both in 

 this country and on the continent. 



Now that the vegetable principle which constitutes the subject 

 of this article has been distinguished by a name, and that the 

 attention of men of science and observation has been turned to 

 it, we may expect to find different species of it exuding from 

 different species of trees besides the elm. The variety which I 

 «m goiag to describe is an example of this. 1 got it from Mr. 

 powerby, who informed me that he collected it from the oak. 



