§§ 244, 245. LICHEN-STARCH, LICHENIN. 251 



carbohydrates are hydroceUuloses, such as are formed from cellulose 

 by the action of concentrated sulphuric acid or chloride of zinc, is 

 a matter for further inquiry. If the treatment with the above 

 oxidizing mixture of chlorate of potash and nitric acid (§ 119) is 

 continued long enough, such substances are always destroyed. 

 Some of them are soluble in boiling water. This is the case 

 with one contained in the asci of certain lichens (Cetraria), etc., 

 from which it is extracted, together with lichenin, by boiling 

 with water ; hence the erroneous idea that the lichenin itself was 

 coloured blue by iodine.^ 



Berg's researches have shown that if a decoction of the lichenin 

 be allowed to gelatinize by cooling, cut into pieces and 

 macerated in distilled water, the whole of the substance that 

 strikes a blue colour with iodine passes into solution, from which 

 it can be isolated by precipitation with alcohol, although impure 

 and not free from ash. After drying it is to a great extent in- 

 soluble in water, and is converted into sugar by boiling with dilute 

 hydrochloric acid (4 per cent, of acid of sp. gr. 1*12) for a period 

 of two hours, a change which is not effected by pure water. The 

 glucose produced is dextro-rotatory, and as the decomposition takes 

 place tolerably smoothly, the amount of the substance, which we 

 may temporarily call lichen-starch, can be determined by estimating 

 the sugar thus formed. Lichen-starch dissolves tolerably easily in 

 ammonia of sp. gr. 0-96, and is precipitated from this solution by 

 spirit. It appears to be more difficultly soluble in dilute alkalies, 

 and is not converted into sugar by diastase or saliva. 



§ 245. Lichenin. — Lichenin is characterized by its property of 

 gelatinizing, which is exhibited by a solution containing 1 in 60. 

 It is insoluble in cold water, alcohol, and ether ; boiling water 

 dissolves it, as do also ammonio-sulphate of copper and concen- 

 trated (20 to 30 per cent.) potash. From its solution in strong 

 potash it can be precipitated by alcohol in the form of a potas- 

 sium-compound containing up to 10 per cent, of alkali. Concen- 

 trated hydrochloric acid also dissolves it, but with simultaneous 

 (partial) decomposition. When boiled with dilute acid it is 

 converted with even more facility than lichen-starch into a dextro- 



^ Compare Berg, ' Zur Kenntniss des in Cetraria islandica vork. Lichenins 

 und iodbläuenden Stoffes,' Diss. Dorpat, 1872. From Berg's experiments it 

 would appear that the formula CßHioOg would indicate the composition of 

 lichen -starch better than C12H22O11 ; the same is true of lichenin. 



