60 
ON THE PROPERTIES OF SILICIC ACID. 
acid to assume alcohol, or even oleine, in the place of water of combination, without 
disintegration or alteration of form, may perhaps afford a clue to the penetration of the 
albuminous matter of membrane by fatty and other insoluble bodies, which seems to 
occur in the digestion of food. Still more remarkable and suggestive are the fluid 
compounds of silicic acid. The fluid alcohol-compound favours the possibility of the 
existence of a compound of the colloid albumen with oleine, soluble also and capable of 
circulating with the blood. 
The feebleness of the force which holds together two substances belonging to different 
physical classes, one being a colloid and the other a crystalloid, is a subject deserving 
notice. When such a compound is placed in a fluid, the superior diffusive energy of the 
crystalloid may cause its separation from the colloid. Thus, of hydrated silicic acid, the 
combined water (a crystalloid) leaves the acid (a colloid) to diffuse into alcohol; and if 
the alcohol be repeatedly changed, the entire water is thus removed, alcohol (another 
crystalloid) at the same time taking the place of water in combination with the silicic 
acid. The liquid in excess (here the alcohol) gains entire possession of the silicic acid. 
The process is reversed if an alcogel be placed in a considerable volume of water. Then 
alcohol separates from combination, in consequence of the opportunity it possesses to 
diffuse into water; and water, which is now the liquid present in excess, recovers 
possession of the silicic acid. Such changes illustrate the predominating influence of 
mass. 
Even the compounds of silicic acid with alkalies yield to the decomposing force of 
diffusion. The compound of silicic acid with 1 or 2 per cent, of soda is a colloidal so¬ 
lution, and, when placed in a dialyser over water in vacuo to exclude carbonic acid, 
suffers gradual decomposition. The soda diffuses off slowly in the caustic state, and 
gives the usual brown oxide of silver when tested with the nitrate of that base. 
The pectization of liquid silicic acid and many other liquid colloids is effected by 
contact with minute quantities of salts in a way which is not understood. On the other 
hand, the gelatinous acid may again be liquefied and have its energy restored by con¬ 
tact with a very moderate amount of alkali. The latter change is gradual, 1 part of 
caustic soda, dissolved in 10,000 water, liquefying 200 parts of silicic acid (estimated 
dry) in 60 minutes at 100° C. Gelatinous stannic acid also is easily liquefied by a 
small proportion of alkali, even at the ordinary temperature. The alkali, too, after 
liquefying the gelatinous colloid, may be separated again from it by diffusion into water 
upon a dialyser. The solution of these colloids, in such circumstances, may be looked 
upon as analogous to the solution of insoluble organic colloids witnessed in animal 
digestion, with the difference that the solvent fluid here is not acid but alkaline. Liquid 
silicic acid may be represented as the “ peptone” of gelatinous silicic acid; and the 
liquefaction of the latter by a trace of alkali may be spoken of as the peptization of 
the jelly. The pure jellies of alumina, peroxide of iron, and titanic acid, prepared by 
dialysis, are assimilated more closely to albumen, being peptized by minute quantities of 
hydrochloric acid. 
Liquid Stannic and Metastannic Acids. —Liquid stannic acid is prepared by dialysing 
the bichloride of tin with an addition of alkali, or by dialysing the stannate of soda 
with an addition of hydrochloric acid. In both cases a jelly is first formed on the 
dialyser ; but, as the salts diffuse away, the jelly is again peptized by the small propor¬ 
tion of free alkali remaining : the alkali itself may be removed by continued diffusion, 
a drop or two of the tincture of iodine facilitating the separation. The liquid stannic 
acid is converted on heating it into liquid metastannic acid. Both liquid acids are re¬ 
markable for the facility with which they are pectized by a minute addition of hydro¬ 
chloric acid, as well as by salts. 
Liquid Titanic Acid is prepared by dissolving gelatinous titanic acid in a small quan¬ 
tity of hydrochloric acid, without heat, and placing the liquid upon a dialyser for several 
days. The liquid must not contain more than 1 per cent, of titanic acid, otherwise it 
spontaneously gelatinizes, but it appears more stable when dilute. Both titanic and 
the two stannic acids afford the same classes of compounds with alcohol, etc., as are ob¬ 
tained with silicic acid. 
Liquid Tungstic Acid. —The obscurity which has so long hung over tungstic acid is 
removed by a dialytic examination. It is in fact a remarkable colloid, of which the 
pectous form alone has hitherto been known. Liquid tungstic acid is prepared by add¬ 
ing dilute hydrochloric acid carefully to a 5 per cent, solution of tungstate of soda, in 
