i813.] 



On Ulmin, 



25 



ulmin in my work, recollected having seen a similar exudation 

 from an old elm in the neighbourhood of Plymouth. Conceiving 

 that this exudation might be ulmin, he collected a quantity of it, 

 and was so obliging as to send it to me. I seized with avidity an 

 opportunity, quite unlocked for, of putting my conjectures to 

 the test of experiment, and of witnessing the very peculiar 

 properties of ulmin described by Klaproth, The substance 

 ^vhich I examintd agrees in so many particulars with the pro- 

 perties noticed by Klaproth, that there can be little doubt of its 

 belonging to the same species. The few differences which I 

 observed were probably owing to the different length of time 

 that the substance in question had been exposed to the atmos- 

 phere. The substance which I examined being an exudation 

 from the common elm, and agreeing in every particular with the 

 properties noticed by Vauquelin, there can be no hesitation in 

 considering them as similar. Hence it follows, that the vegetable 

 substance first described by Vauquelin, and the ulmin of Klap- 

 roth, are one and the same. 



The following are the properties of the ulmin from Plymouth, 

 -as far as I observed them : — 



1. It was of a black colour, possessed considerable lustre, and 

 broke with a vitreous fracture. It w^as nearly tasteless, leaving 

 in the mouth only a very slight impression of astringency. When 

 heated it did not melt, but swelled very much, as is the case 

 with gum. It readily burnt away at the flame of a candle, 

 leaving a white matter, which melted into an opake white bead, 

 and was carbonate of potash. The proportion of this alkali was 

 considerable, agreeing exactly with the exudation examined by 

 Vauquelin. It contained also lime : 20 grains of the ulmin when 

 burnt in a platinum crucible left 5 grains of residue. Of this 

 4*8 grains dissolved in nitric acid. The 0*2 grain of residue was 

 insoluble, and possessed the properties of silica, tinged a little 

 with iron. The nitric acid solution being saturated with car- 

 bonate of potash, one grain of carbonate of lime precipitated. 

 Hence 20 grains of ulmin contained the following substances: — 



Subcarbonate of potash S'8 



Carbonate of lime TO 



Silica and oxide of iron * .... .0*2 



5-0 



The silica and iron were probably accidentally present, and 

 might have made their way to the ulmin while moist upon the 

 tree ; for it is probable that the dust of the road would con- 

 sist chiefly of silica ; or at least would be insoluble in nitric acid, 

 the only criterion by which the 0'2 grains of residue were judged 

 to be silica. 



2, It dissolved readily in water. The solution was dark brown^ 



