216 
ME. T. GEAHAM ON LIQUID DIFFUSION APPLIED TO ANALYSIS. 
portion of water. In the analysis by Gelis of his carameline, 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 crystalloidal reagents which is witnessed in fluid silicic acid 
and alumina. The solution 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 pre- 
cechng properties not being observed in crude caramel. This colloid appears also to be 
precipitated 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 is dialysed, the potash is quickly reduced to the proportion of about 
9 per cent., which forms a neutral compound. If an excess of acetic acid now be added, 
the whole potash is soon diffused away, and pure soluble caramel remains on the dia- 
lyser. Even carbonic acid will carry away the potash. 
The extremely low diflusibility which has been assigned to caramel in former Tables, 
belongs to that substance as last described ; the brown intermediate substances which 
accompany it in crude caramel being considerably more diffusive, although they again 
are much less diffusive than any variety of crystallizable or uncrystallizable sugar. 
When the molasses of the cane-sugar are diflused, much the greater portion of the 
colouring matters remains in the dialyser. 
With the parchment-paper septum the fluid caramel appeared even less dialysable 
than gum, the difiusate in twenty-four hours from a 2 per cent, solution of the former 
being '009 gramme only, while that of the latter was •013. Caramel may be stated, 
approximately, to be 600 times less dialysable than chloride of sodium, and 200 times 
less so than sugar. Hence liquids coloured with caramel, such as porter and coflee, 
may be dialysed for a day with the passage of very little colouring matter. 
Before leading caramel, the analogy may be referred to which the insoluble form of 
that substance presents to coal. Caramelization appears the first step in that direction, 
— the beginning of a colloidal transformation to be consummated in the slow lapse of 
geological ages. 
Albumen . — The purification of albumen is effected with much advantage upon the dia- 
lyser. The solution of egg-albumen is mixed freely mth acetic acid and then dialysed. 
The earthy and alkaline salts are speedily got rid of, and in three or four days the 
albumen burns without leaving a trace of ash. Although the acetic acid used in the 
process appears to difiuse ofl entirely, albumen prepared in the manner described has a 
faint acid reaction. It also coagulates milk when mixed with the latter and heated. 
Albumen so prepared retains its constituent sulphur. 
The passage through parchment-paper of pure albumen prepared by the unobjection- 
