LICHENS AS FOOD. 215 



idded to the fluid, do not dissolve unless it be boiling; 

 a fact which confirms the opinion that this species of mucilage 

 is less soluble than any with which we are acquainted in the 

 vegetable kingdom. Unlike every one of the known gums or 

 mucilages, this jelly, when concentrated, is not viscid, either 

 cold or hot, and it may therefore be doubted whether it would 

 be useful in the arts, unless for calico printing ; a point which 

 deserves to be examined*. From this want of viscidity it 

 happens that the jelly, when dried upon plates, divides into 

 transparent angular and brittle fragments of a deep red colour. 

 The animal or vegetable jellies differ extremely from it in this 

 respect, because the viscidity, which connects their^parts, pre- 

 vents their separating while drying. 



If the dried gum of the lichen be thrown into hot or cold Habitude of (he 

 water it does not dissolve, but it softens and swells up, with- (^ned gum wiUi 

 out becoming viscid or tenacious ; but it deposits very speedily 

 all its extractive matter, and consequently its bitterness. This 

 property affords a means of purifying it in case it should here- 

 after be found of service in the arts. 



The infusion of galls, which has no action upon the known The green is 



gums, instantly precipitates the iellyof the lichen, and affords P^^fcipuable by 



■,. - ^ ./ . , .■',,. ^ . , . , . ,.^ galls, but the 



a white mass, as with anmial jellies; but there is this diffe- precipitate is 



fence, that the new combination dissolves in hot water, and soluble in liot- 

 separates by cooling. In this fact we have a character of the 

 mucilage of lichen, which seems to assimulate it with that of 

 animal matters; but the following experiments decide other- 

 wise. 



The gum of lichen, heated in a retort, is destroyed without Products by 

 being softened. Like gum arable it leaves only 23 or 24 ^^s'^^ctive 

 hundredths of charcoal. Its products do not differ from those 

 of gum or starch; that is to say, they consist in water and 

 vinegar of the same odour; but the oil appeared to be much 

 more abundant. Potash separates from this vinegar only a kvi; 

 atoms of ammonia. 



The nitric acid readily converts it into very white oxalic vru •„„ -j 

 acid, leaving no tallow, or yellow bitter principle, in the duces the axa- 



. , late. 

 residue. 



* The jelly of lichens was examined eight or nine years ago by 

 Lord Dundonald, and offered for this purpose to the calico printers. 



