190 Dr Thomson on Parietin^ 



0.47 grains of a skeleton, answering to the form of the lichen, 

 and consisting of silica and phosphates, &c. These three 

 experiments, therefore, give a per-centage respectively of 

 ashes, amounting to 6.8, 6.75, and 6.71.* In all these trials, 

 the colouring matter was volatilized before the lichen caught 

 fire. Another specimen, very carefully washed, and -consist- 

 ing of the upper parts of fronds, yielded 5 per cent, of ash, in 

 which phosphate of alumina formed a prominent ingredient. 

 In proof of the fact that the ash is in no degree connected 

 with the rock, a specimen of Parmelia omphalodes, taken from 

 the stem of an ash tree, ten feet from the ground, was ignited, 

 and found to yield 7 per cent, of ash, consisting of silica, 

 phosphates of lime, iron, and alumina. The Cladonia pixi- 

 data, taken from a wall, and free from all extraneous sub- 

 stances, yielded 6 per cent, of ashes, consisting of similar 

 ingredients. Hence it would appear, that this species of 

 plants contain no inconsiderable amount of substances calcu- 

 lated to serve as vegetable manure. The ash possessed the 

 form of the lichen, and a slight iron tint ; it effervesced 

 slightly on the addition of an acid. In one instance, some 

 carbonate of lime was present. On digesting the ash in water, 

 a minute portion was dissolved. This solution, on the addi- 

 tion of chloride of barium, gave a white precipitate, part of 

 which was insoluble in nitric acid. On throwing the sulphate 

 of barytes on a filter, and adding caustic ammonia to the fil- 

 tered liquid, a flocky precipitate — phosphate of barytes — fell. 

 The addition of an alcoholic solution of bichloride of platinum 

 gave no indication of the presence of potash. Nitrate of 

 silver gave a flocky precipitate, insoluble in nitric acid. The 

 soluble salts, therefore, appear to be sulphate and phosphate 

 of soda and common salt. The portion of the residue insolu- 

 ble in water, became nearly white when boiled with dilute 

 muriatic acid, and left a gritty powder, which, affording a 

 nearly colourless glass with carbonate of soda before the blow- 

 pipe, was obviously silica, with slight impurity. The muriatic 

 acid solution gave a copious reddish precipitate, with caustic 

 ammonia. This precipitate was partly soluble in caustic 



* These determinations were made in conjunction with Mr James 

 Murdoch. 



