370 Mr. T. Graham on Liquid Diffusion applied to Analysis. 



The crude caramel obtained by heating cane-sugar at 210°- 

 220°, when placed on the dialyscr, allows certain intermediate 

 coloured substances (Caramelane and Caramclene of Gelis) to 

 diffuse out with considerable facility, while the compound con- 

 taining the largest proportion of carbon remains behind. The 

 latter substance, as obtained by me, possessed five times the 

 colouring-power of the original crude caramel, weight for weight. 

 This highest soluble member of the caramel series may also be 

 obtained, more quickly, by precipitation from its aqueous solution 

 by means of alcohol. But I found it necessary to repeat the 

 precipitation four times, or till the mass thrown down, from being 

 plastic at first, became pulverulent. A solution containing 10 

 per cent, of the caramel so purified is gummy; and on standing, 

 it formed a tremulous jelly entirely soluble in hot or cold water. 

 Evaporated in vacuo, the solution dries up into a black shining 

 mass, which is tough and elastic, while it still possesses a certain 

 proportion of water, like gum containing some water. Once 

 thoroughly dried at a low temperature, this soluble caramel may 

 be heated, afterwards, to 120° and retain complete solubility. 

 But if a solution of the same caramel be directly evaporated to 

 dryness by the heat of a water-bath, the whole matter is rendered 

 insoluble in hot or cold water. The soluble and insoluble 

 caramel have the same composition, and appear to illustrate the 

 usual double form of colloids. The proportion of carbon in the 

 fluid caramel was found as high as 54*59 per cent., which comes 

 nearer to C 24 H 16 O 15 (requiring C 55*17) than any other formula 

 in which the oxygen and hydrogen are assumed to be present in 

 the proportion of water. In the analysis by Gelis of his cara- 

 meline, the proportion of carbon did not exceed 51*33 per cent., 

 which does not apply to the present substance. 



Fluid caramel is wholly tasteless, and appears to be neutral. 

 It exhibits the same excessive sensibility to crystalloid al reagents 

 which is witnessed in fluid silicic acid and alumina. The solu- 

 tion is precipitated or pectized by mere traces of any mineral 

 acid, by alkaline sulphates, chloride of sodium, by most other 

 salts, and by alcohol. The caramel then forms a brownish 

 black pulverulent substance, insoluble in hot or cold water. 

 The presence of sugar and of the intermediate brown substances 

 protects fluid caramel in a remarkable way from the action of 

 crystalloids, and accounts for the preceding properties not being 

 observed in crude caramel. This colloid appears also to be pre- 

 cipitated by certain substances of its own class, such as peroxide 

 of iron. 



Pectous caramel may readily have its solubility restored. 

 Placed in dilute potash, the caramel swells and appears gelatinous, 

 and is dissolved on the application of heat. When this solution 



