THE PROPERTIES OF COLLOIDS 



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C.) The concentrated S erun left behind i & W ? u . <!0r " > <" 



mometer, the filtrate being used LThet^tfd Th S^T 'r",", """ "" ~ 

 is shown in the diagram (Fig. 27). " of the """ 



The tube BB is made of silver gauze, connected at each end to a tube of *> 

 Round the gauze is wrapped a piece of peritoneal membrane, a, in mating ' 

 Th,s punted all over with a solution of gelatin (10 per cent.) and ^7^31" 

 of membrane apphed. Fme thread is now twisted many times round Z"ube to 



prevent any disturbance of the membranes, and the whole tube is soaked for half an 

 hour in a warm solution of gelatin. In this way one obtains an even layer of gelatin 

 between two layers of peritoneal membrane and supported by the wire gauze. The 

 tube so prepared is placed within a wide tube, AA, which is provided with two tubules 

 at the top. One of these, 0, is for filling the outer tube ; the other is fitted with 

 a mercurial manometer, M. Two small reservoirs, CC, are connected with the outer 

 ends of BB, by means of rubber tubes. The whole apparatus is placed in a wooden 

 cradle, DD, pivoted at X, and provided with a cover so that it may be filled with fluids 

 at different temperatures if necessary. The colloid solution is placed in AA, and the 

 reservoirs, CC, and inner tube, BB, are filled with the filtrate, i.e. with a salt solution 

 approximately or absolutely isotonic with the colloid solution. The apparatus is then 

 made to rock continuously for days or weeks by means of a motor. In this way the 

 fluid on the two sides of the membrane is continually renewed, and the attainment 

 of an osmotic equilibrium facilitated. With this apparatus I found that the colloids 

 in blood-serum, containing from 7 to 8 per cent, proteins, had an osmotic pressure of 

 25 to 30 mm. Hg., which would correspond to a molecular weight of about 30,000. 



A more convenient form of osmometer has been devised by B. Moore, 

 using parchment paper as the membrane. With this osmometer, the 

 existence of an osmotic pressure in colloidal solutions has been definitely 

 established both by Moore in the case of haemoglobin, proteins, and soaps, 

 and by Bayliss in the case of colloidal dyes, such as Congo red. The osmotic 

 pressure of haemoglobin was found by Hiifner to correspond to a molecular 

 weight of about 16,000, i.e. a molecular weight already deduced from il 

 composition and its combining powers with oxygen. Often, however, ti 

 osmotic pressure is very much smaller than would be expected from th- 

 molecular weight of the substance, owing to the fact that colloids in solution 



