1854.] 



BAKERIAN LECTURE— ON OSMOTIC FORCE. 



13 



are surpassed by the stronger mineral acids, such as sulphuric and 

 phosphoric acid, and sulphate of potash ; wliich are again exceeded 

 by salts of potash and soda, possessing either a decided acid or allculine 

 reaction, such as binoxalate of potash, pliosphate of soda, and carbo- 

 nates of potash and soda. The highly osmotic substances were also 

 found to act with most advantage in small proportions, producing in 

 general the largest osmose in the proportion of one-quarter per cent, of 

 salt dissolved. Osmose is, indeed, eminently the phenomenon of weak 

 solutions. The same substances are likewise always chemically active 

 bodies, and possess aiEaities which enable them to act upon the mate- 

 rial of the earthenware septum. Lime and alumina were accordingly 

 always found in solution after osmose, and the corrosion of the septum 

 appeared to be a necessary condition of the flow. Septa of other mate- 

 rials, such as pure carbonate of lime, gypsum, compressed charcoal, and 

 tanned sole-leather, although not deficient in porosity, gave no osmose, 

 apparently because they are not acted upon chemically by the saline 

 solutions. Capillarity alone was manifestly insufBcient to produce the 

 liquid movement, while the vis motrix appeared to be chemical action. 

 Tiie electrical endosmose of Porrett, which has lately been defined with 

 great clearness by Weideraann, was believed to indicate the possession 

 of a peculiar chemical constitution by water, while liquid, or at least 

 the capacity to assume that constitution when water is poralized and 

 acting chemically upon other substances. A large but variable number of 

 atoms of water are associated together to form a liquid molecule of water, 

 of which an individual atom of oxygen stands apart, forming a negative 

 or chlorous radical, while the whole remaining atoms together arc 

 constituted into a positive or basylous radical ; — -which last wili contain 

 an unbalanced equivalent of hydrogen giving the molecule basicity, as 

 in the great proportion of organic radicals. Now, it is this volumi- 

 nous basylous radical, which travels in the electrical decomposition of 

 pure water, and resolves itself into hydrogen gas and water at the 

 negative pole, causing the accumulation of water observed there; 

 while the oxygen alone proceeds in the opposite direction to the 

 positive polo. Attention was also called to the fact, that acids and 

 alkalies, when in solution, are chemically combined with much water 

 of hydration ; sulphuric acid, for instance, evolving heat when the 

 fiftieth equivalent of water is added to it. In the combination of such 

 bodies, the disposal of the water is generally overlooked. Osmose was 

 considered as depending upon such secondary results of combination ; 

 that is, upon the large number or voluminous proportions of the water 

 molecules involved in such combinations. The porous septum is the 

 mean's of bringing out and rendering visible, both in electrical and 

 ordinary osmose, this liquid movement attending chemical combinations 

 and decompositions. Although the nature and modus operandi of the 

 chemical action producing osmose remains still very obscure, considerable 

 light is thrown upon it in tlie application of septa of animal membrane. 

 Ox bladder was found to acquire greatly increased activity, and also 

 to act with much greater regularity, when first divested of its outer 

 muscular coat. Cotton calico also, impregnated with liquid albumen, 

 and afterwards exposed to heat, so as to coagulate that substance, was 

 sutficiently impervious, and formed an excellent septum, resembling 

 membrane in every respect. The osmometer was of the usual bulb- 

 form, but the membrane was supported by a plate of perforated zinc, 

 and the instrument provided with a tube of considerable diameter. 

 The diameter of the tube being one-tenth of that of the mouth of the 

 bidb or disc of membrane exposed to the fluids, a rise of liquid in 

 the tube amounting to 100 millimetres indicated that as much water 

 had permeated the membrane .and entered the osmometer as would 

 cover the whole surface of the membrane to a depth of one millimetre, 

 or one twenty-fifth part af an inch, Such millimetre divisions of the 

 tube become degrees of osmose, which are of the same value in all 

 instrumeuts. Osmose in membrane presented many points of similarity 

 to that in earthenware. The membrane is constantly undergoing 

 decomposition, and its osmotic action is inexhaustable. Further, 

 salts and other substances capal)le of detrrmining a large osmose are 

 all chemically active substances, while tlie great mass of neutral 

 monobasic salts of the metals, such as chloride of sodium, possess 

 only a low degree of action, or are wholly inert. The active sub- 

 stances arc also relatively most efficient in small proportions. Wlicn 

 a solution of the proper kind is used, the osmose or passage of fluid 

 proceeds with a velocity wholly unprecedented in such experiments. 

 The rise of liquid in the tube with a solution containing one-tenth per 

 cant, of carbonate of potash in the o>niometer, was 107 degrees or 

 millimetres, and with oui per cent, of the same salt, 20(i degrees in 

 fiv-i hours. With anoth-^r membrane and stronger solution the rise 

 was 8.5^! millimetres, oi- u.iw.irds of 00 iiidies, in I'.io same time ; and 

 as much water tlieroforj was imnelled through the niombrane as 



would cover its whole surface to a depth of 8-0 niilliraetrcs, or one 

 third of an inch. The chemical action must be diiferent on the sub- 

 stance of the membrane at its inner and outer surfaces to induce 

 osmose ; and according to the hypothetic view which accords best with 

 the phenomenon, the action on the two sides is not unequal in degree 

 only, but also difterent in kind. It appears as an alkaline action on 

 the albuminous substance of the membrane, at the inner surface, and 

 as an acid action on the albumen at the outer surface. The most 

 general empirical conclusion that can be drawn is, that the water 

 always accumulates on the alkaline or basic side of the membrane. 

 Hence, with an alkaline salt, such as carbonate or phosphate of soda, 

 in the osmometer and water outside, the flow is inwards ; but with 

 an acid in the osmometer, on the contrary, the flow is outwards, or 

 there is negative osmose, the liquid then falling in the tube. In the 

 last case, the water outside is basic when compared mth the acid 

 within, and the flow is therefore still towards the base. The chloride 

 of sodium, chloride of barium, chloride of magnesium, and similar 

 neutral salts, are wholly indifferent, or appear only to act in a subor- 

 dinate manner to some other active acid or basic substance, — which 

 last may be present in the solution or mcmbi'ane in the most minute 

 quantity. Salts which admit of dividing into a basic subsalt and free 

 acid exhibit an osmotic activity of the highest order. Such arc the 

 acetate and various other salts of alumina, iron and chromium, the 

 protochloride of iron, chloride of copper and tin, chloride of copper, 

 nitrate of lead, &c. The acid travels outwards by difi"usion, superin- 

 ducing a basic condition of the inner surface of the membrane and an 

 acid condition of the outer surface, the favourable condition of a high 

 positive osmose. The bibasic salts of potash and soda again such as 

 the sulphate and tartrate of potash, although strictly neutral in pro- 

 perties, begin to exhibit a positive osmose, in consequence, it may be 

 presumed, of their resolution into an acid supersalt and free alkaline 

 base. The following table exhibits the osmose of substances of all 

 classes : 



Osmose of 1 per cent. Solutiom in Membrane. 



Oxalic Acid ----------- — 148 degrees 



Hydrochloric Acid --------- — 92 



Terchloride of Gold - - - - — 5-1 



Bichloride of Tin — 46 



Bichloride of Platinum -------- — 30 



Chloride of JIagnesium -------- — 3 



Chloride of Sodium -f- 2 



Chloride of Potassium -------- 18 



Nitrate of Soda --- 2 



Nitrate of silver ---------- 34 



Sulphate of Potash 21 to 60 



Sulphate of Magnesia -------- 14 



Chloride of Calcium - - 20 



Chloride of Barium --------- 21 



Chloride of Strontium -------- 26 



Chloride of Cobalt - - 26 



Chloride of Manganese -------- 34 



Chloride of Zinc 54 



Chloride of Nickel &S 



Nitrate of Lead ---------- 12-5 to 211 



Nitrate of Cadmium --------- 137 



Nitrate of Uranium 234 to 458 



Nitrate of Copper- - - 204 



Chloride of Copper --------- 351 



Protochloride of Tin 289 



Protochloride of Iron -- 435 



Chloride of Mercury 121 



Protonitratc of Mercury ------- 850 



Pornitrate of Mercury -------- 47ii 



Acetate of Sesquioxidc of Iron ----- l'J4 



Acetate of Alumina - - - - 280 to 393 



Chloride of Aluminum -------- 540 



Phosphate of Soda --------- oil 



Carbonate of Potash -------- 43'J 



It may appear to some, that the chemical character which has liocn 

 assigned to osmose takes awny from the physiologicnl interest of the 

 subject in so far as the decomposition of the membrane may appear to 

 be incompatible witli vital conditions, and that osmotic movements 

 must therefore be confined to dead matter; but such apprehensions 

 are, it is believed, groundless, or at all events premature. .Ul partji 

 of living structures are allowed to be in a slate of incos-snnt chanco of 

 decomposition and renewal. The decomposition occurring in n living 



