212 DEXTRIN, TBITICIN, ETC. 



chloride of sp. gr. 1-2; a cloudiness or precipitate produced in 

 some samples {e.g. Feronia elephantiim) is probably due to con- 

 tamination. Silicate of potash (1 part of thick soluble glass 

 diluted Tcith 20 parts of water) produces in solutions of gum 

 arabic, and most of its surrogates, a cloudiness or precipitate 

 which partially or wholly redissolves on adding excess. Arabic 

 acid remains clear, or becomes only slightly turbid. The same 

 reagent does not precipitate the partially soluble gum from 

 species of Cactus, Cedrela, or Ehizophora, or solutions of the gum 

 from Acacia catechu, A. leucophloea, and species of Albizza, 

 Azedirachta, Odina and Conocarpus. A 2 per cent, solution of 

 stannate of potash yields reactions resembling in general those of 

 silicate of potash, but produces in solutions of arabic acid a pre- 

 cipitate that redisstflves in excess. A 10 per cent, solution of 

 neutral sulphate of aluminium gives, as a rule, a precipitate, and 

 this is in many cases soluble in caustic potash of sp. gr. 1'13. 

 Basic acetate of lead also produces a precipitate, which is generally 

 partially or wholly soluble in excess. 



§ 197. Separation from Dexfrim, etc. — The behaviour of the muci- 

 laginous substances soluble in water to basic acetate of lead 

 furnishes us with the means of getting rid of them, should we 

 wish to make optical or chemical experiments with extracts of 

 vegetable substances for the detection of glucose, sacchajrose, dextrin, 

 iriticin, etc. (cf. §§ 76, 83) ; care must be taken, however, not to 

 add any large excess of the precipitant. If this precaution is 

 observed, such substances as arabin and dextrin can, I think, be 

 more completely separated than by the precipitation with alcohol, 

 recommended in §§ 75, 76. In the latter, ethylio alcohol can, as 

 I showed some years since, be replaced by methylic.^ 



DEXTETN, TRITICIN, SINISTEIN, LEVULIN. 



§ 198. Characters. — These carbohydrates are all easily converted 

 into glucoses (§ 76) by dilute acids. Dextrin may be distinguished 

 by its yielding grape-sugar, whilst triticin, sitii^trin and levulin 

 are converted into levnlose, and are also characterized by their 

 behaviour to baryta-water (see also § 77). Levulin ^ is optically 



1 Pharm. Zeitschr. f. Bussland, iv. 152, 1866. (note). 



2 Compare Weyher v. Eeidemeister, ' Beitr. z. Kenntniss d. Levulins, etc' 

 Diss. Dorpat, 1880. 



