30 ON VEGETABLE IHr( It.AGKS. 



Tragacanth. Traj^acauth is, in many of its physical properties, consi- 



derably dift'erent iVom gum arable, and its habitudes with 

 the chemical reagents appear to be^o less dissimilar. Wn- 

 ter dissolves this substance with so much difificulty, that it 

 hea been said to be absolutely insoluble f. When traga- 

 canth is digested in water, it absorbs a large quantity of the 

 fluid, and is greatly increased in bulk, but even after being 

 kept for sorrie time at the boiling temperature, no proper 

 When soften- solution seems to be produced. If, however, the tragacanth 

 in water' m^y ^" *^'^ softened state be strongly rubbed in a mortar with an 

 bedis-:o]ved by additional quar^tity of fluid, a real combination appears to 

 tnturutiun. -^^ effected ; a mucilage is formed, which possesses a homo- 

 geneous consistence, and retains the same state for several 

 weeks, without manifesting any tendency to subsidence. A 

 1 part to If^O: >jjy(.j|jjp.g ^f ^\^\^ kind was made with I part of trao-acantlr 



equal to 10 of ^ . ' ^, 



gum arabic. ^^ 100 parts oi water; it was of about tne same consistence 



with that composed of 1 part of gum arable to 10 parts of 



water. To this mucilage the same <J reagents were added 



Effects of rea- as in the former experiments. In No. 1 a copious dense 



gents on t xe precipitate was instantly produced. In No. 2 there was a 

 solution. ^. ^ " . 



slight degree of coagulation, and a precipitate, which was 



increased in the space of 24 hours. In No. 3 a firm coagu- 

 lum was instantly formed. No elfect was produced in No. 

 4, except the mucilage was extremely dense, when its colour 

 was changed to a dusky gray, and afterward to a blackish 

 purple ; but without any precipitation or coagulation. lu 

 . the same manner the oxysulphate of iron produced no ef- 

 fect, except the mucilage was of a very strong consistence, 

 when its colour was changed to a deep brown; but there was 

 no precipitate or coagulum. The nitrate of mercury threw 

 down a slight precipitate of a reddish tinge. Silicated pot- 

 ash produced HO efl'ect, except a very strong solution was 

 employed, when there was a degree of opacity produced; 

 bat the same was observable upon the addition of caustic 

 potash. It was difficult to asce-.tain the elfect of alcohol 

 upon tragacanth, because, however ci»refully the mucilage 

 JL greater per- was prepared, any farther addition of fluid would not incor- 



tion of fluid uofate with it, but produced un aiipearance of precipitation. 

 , "would not in * 



♦ Duncan^- Dispensatory, p. 182. Thoi*:-ou'» Chemistry, V. 46. 



In 



